diff options
Diffstat (limited to 'kernel/futex.c')
| -rw-r--r-- | kernel/futex.c | 3175 |
1 files changed, 2671 insertions, 504 deletions
diff --git a/kernel/futex.c b/kernel/futex.c index 5efa2f97803..b632b5f3f09 100644 --- a/kernel/futex.c +++ b/kernel/futex.c @@ -8,6 +8,21 @@ * Removed page pinning, fix privately mapped COW pages and other cleanups * (C) Copyright 2003, 2004 Jamie Lokier * + * Robust futex support started by Ingo Molnar + * (C) Copyright 2006 Red Hat Inc, All Rights Reserved + * Thanks to Thomas Gleixner for suggestions, analysis and fixes. + * + * PI-futex support started by Ingo Molnar and Thomas Gleixner + * Copyright (C) 2006 Red Hat, Inc., Ingo Molnar <mingo@redhat.com> + * Copyright (C) 2006 Timesys Corp., Thomas Gleixner <tglx@timesys.com> + * + * PRIVATE futexes by Eric Dumazet + * Copyright (C) 2007 Eric Dumazet <dada1@cosmosbay.com> + * + * Requeue-PI support by Darren Hart <dvhltc@us.ibm.com> + * Copyright (C) IBM Corporation, 2009 + * Thanks to Thomas Gleixner for conceptual design and careful reviews. + * * Thanks to Ben LaHaise for yelling "hashed waitqueues" loudly * enough at me, Linus for the original (flawed) idea, Matthew * Kirkwood for proof-of-concept implementation. @@ -40,72 +55,254 @@ #include <linux/pagemap.h> #include <linux/syscalls.h> #include <linux/signal.h> +#include <linux/export.h> +#include <linux/magic.h> +#include <linux/pid.h> +#include <linux/nsproxy.h> +#include <linux/ptrace.h> +#include <linux/sched/rt.h> +#include <linux/hugetlb.h> +#include <linux/freezer.h> +#include <linux/bootmem.h> + #include <asm/futex.h> -#define FUTEX_HASHBITS (CONFIG_BASE_SMALL ? 4 : 8) +#include "locking/rtmutex_common.h" /* - * Futexes are matched on equal values of this key. - * The key type depends on whether it's a shared or private mapping. - * Don't rearrange members without looking at hash_futex(). - * - * offset is aligned to a multiple of sizeof(u32) (== 4) by definition. - * We set bit 0 to indicate if it's an inode-based key. - */ -union futex_key { - struct { - unsigned long pgoff; - struct inode *inode; - int offset; - } shared; - struct { - unsigned long uaddr; - struct mm_struct *mm; - int offset; - } private; - struct { - unsigned long word; - void *ptr; - int offset; - } both; -}; + * READ this before attempting to hack on futexes! + * + * Basic futex operation and ordering guarantees + * ============================================= + * + * The waiter reads the futex value in user space and calls + * futex_wait(). This function computes the hash bucket and acquires + * the hash bucket lock. After that it reads the futex user space value + * again and verifies that the data has not changed. If it has not changed + * it enqueues itself into the hash bucket, releases the hash bucket lock + * and schedules. + * + * The waker side modifies the user space value of the futex and calls + * futex_wake(). This function computes the hash bucket and acquires the + * hash bucket lock. Then it looks for waiters on that futex in the hash + * bucket and wakes them. + * + * In futex wake up scenarios where no tasks are blocked on a futex, taking + * the hb spinlock can be avoided and simply return. In order for this + * optimization to work, ordering guarantees must exist so that the waiter + * being added to the list is acknowledged when the list is concurrently being + * checked by the waker, avoiding scenarios like the following: + * + * CPU 0 CPU 1 + * val = *futex; + * sys_futex(WAIT, futex, val); + * futex_wait(futex, val); + * uval = *futex; + * *futex = newval; + * sys_futex(WAKE, futex); + * futex_wake(futex); + * if (queue_empty()) + * return; + * if (uval == val) + * lock(hash_bucket(futex)); + * queue(); + * unlock(hash_bucket(futex)); + * schedule(); + * + * This would cause the waiter on CPU 0 to wait forever because it + * missed the transition of the user space value from val to newval + * and the waker did not find the waiter in the hash bucket queue. + * + * The correct serialization ensures that a waiter either observes + * the changed user space value before blocking or is woken by a + * concurrent waker: + * + * CPU 0 CPU 1 + * val = *futex; + * sys_futex(WAIT, futex, val); + * futex_wait(futex, val); + * + * waiters++; (a) + * mb(); (A) <-- paired with -. + * | + * lock(hash_bucket(futex)); | + * | + * uval = *futex; | + * | *futex = newval; + * | sys_futex(WAKE, futex); + * | futex_wake(futex); + * | + * `-------> mb(); (B) + * if (uval == val) + * queue(); + * unlock(hash_bucket(futex)); + * schedule(); if (waiters) + * lock(hash_bucket(futex)); + * else wake_waiters(futex); + * waiters--; (b) unlock(hash_bucket(futex)); + * + * Where (A) orders the waiters increment and the futex value read through + * atomic operations (see hb_waiters_inc) and where (B) orders the write + * to futex and the waiters read -- this is done by the barriers in + * get_futex_key_refs(), through either ihold or atomic_inc, depending on the + * futex type. + * + * This yields the following case (where X:=waiters, Y:=futex): + * + * X = Y = 0 + * + * w[X]=1 w[Y]=1 + * MB MB + * r[Y]=y r[X]=x + * + * Which guarantees that x==0 && y==0 is impossible; which translates back into + * the guarantee that we cannot both miss the futex variable change and the + * enqueue. + * + * Note that a new waiter is accounted for in (a) even when it is possible that + * the wait call can return error, in which case we backtrack from it in (b). + * Refer to the comment in queue_lock(). + * + * Similarly, in order to account for waiters being requeued on another + * address we always increment the waiters for the destination bucket before + * acquiring the lock. It then decrements them again after releasing it - + * the code that actually moves the futex(es) between hash buckets (requeue_futex) + * will do the additional required waiter count housekeeping. This is done for + * double_lock_hb() and double_unlock_hb(), respectively. + */ + +#ifndef CONFIG_HAVE_FUTEX_CMPXCHG +int __read_mostly futex_cmpxchg_enabled; +#endif /* - * We use this hashed waitqueue instead of a normal wait_queue_t, so + * Futex flags used to encode options to functions and preserve them across + * restarts. + */ +#define FLAGS_SHARED 0x01 +#define FLAGS_CLOCKRT 0x02 +#define FLAGS_HAS_TIMEOUT 0x04 + +/* + * Priority Inheritance state: + */ +struct futex_pi_state { + /* + * list of 'owned' pi_state instances - these have to be + * cleaned up in do_exit() if the task exits prematurely: + */ + struct list_head list; + + /* + * The PI object: + */ + struct rt_mutex pi_mutex; + + struct task_struct *owner; + atomic_t refcount; + + union futex_key key; +}; + +/** + * struct futex_q - The hashed futex queue entry, one per waiting task + * @list: priority-sorted list of tasks waiting on this futex + * @task: the task waiting on the futex + * @lock_ptr: the hash bucket lock + * @key: the key the futex is hashed on + * @pi_state: optional priority inheritance state + * @rt_waiter: rt_waiter storage for use with requeue_pi + * @requeue_pi_key: the requeue_pi target futex key + * @bitset: bitset for the optional bitmasked wakeup + * + * We use this hashed waitqueue, instead of a normal wait_queue_t, so * we can wake only the relevant ones (hashed queues may be shared). * * A futex_q has a woken state, just like tasks have TASK_RUNNING. - * It is considered woken when list_empty(&q->list) || q->lock_ptr == 0. - * The order of wakup is always to make the first condition true, then - * wake up q->waiters, then make the second condition true. + * It is considered woken when plist_node_empty(&q->list) || q->lock_ptr == 0. + * The order of wakeup is always to make the first condition true, then + * the second. + * + * PI futexes are typically woken before they are removed from the hash list via + * the rt_mutex code. See unqueue_me_pi(). */ struct futex_q { - struct list_head list; - wait_queue_head_t waiters; + struct plist_node list; - /* Which hash list lock to use. */ + struct task_struct *task; spinlock_t *lock_ptr; - - /* Key which the futex is hashed on. */ union futex_key key; + struct futex_pi_state *pi_state; + struct rt_mutex_waiter *rt_waiter; + union futex_key *requeue_pi_key; + u32 bitset; +}; - /* For fd, sigio sent using these. */ - int fd; - struct file *filp; +static const struct futex_q futex_q_init = { + /* list gets initialized in queue_me()*/ + .key = FUTEX_KEY_INIT, + .bitset = FUTEX_BITSET_MATCH_ANY }; /* - * Split the global futex_lock into every hash list lock. + * Hash buckets are shared by all the futex_keys that hash to the same + * location. Each key may have multiple futex_q structures, one for each task + * waiting on a futex. */ struct futex_hash_bucket { - spinlock_t lock; - struct list_head chain; -}; + atomic_t waiters; + spinlock_t lock; + struct plist_head chain; +} ____cacheline_aligned_in_smp; + +static unsigned long __read_mostly futex_hashsize; -static struct futex_hash_bucket futex_queues[1<<FUTEX_HASHBITS]; +static struct futex_hash_bucket *futex_queues; -/* Futex-fs vfsmount entry: */ -static struct vfsmount *futex_mnt; +static inline void futex_get_mm(union futex_key *key) +{ + atomic_inc(&key->private.mm->mm_count); + /* + * Ensure futex_get_mm() implies a full barrier such that + * get_futex_key() implies a full barrier. This is relied upon + * as full barrier (B), see the ordering comment above. + */ + smp_mb__after_atomic(); +} + +/* + * Reflects a new waiter being added to the waitqueue. + */ +static inline void hb_waiters_inc(struct futex_hash_bucket *hb) +{ +#ifdef CONFIG_SMP + atomic_inc(&hb->waiters); + /* + * Full barrier (A), see the ordering comment above. + */ + smp_mb__after_atomic(); +#endif +} + +/* + * Reflects a waiter being removed from the waitqueue by wakeup + * paths. + */ +static inline void hb_waiters_dec(struct futex_hash_bucket *hb) +{ +#ifdef CONFIG_SMP + atomic_dec(&hb->waiters); +#endif +} + +static inline int hb_waiters_pending(struct futex_hash_bucket *hb) +{ +#ifdef CONFIG_SMP + return atomic_read(&hb->waiters); +#else + return 1; +#endif +} /* * We hash on the keys returned from get_futex_key (see below). @@ -115,7 +312,7 @@ static struct futex_hash_bucket *hash_futex(union futex_key *key) u32 hash = jhash2((u32*)&key->both.word, (sizeof(key->both.word)+sizeof(key->both.ptr))/4, key->both.offset); - return &futex_queues[hash & ((1 << FUTEX_HASHBITS)-1)]; + return &futex_queues[hash & (futex_hashsize - 1)]; } /* @@ -123,134 +320,775 @@ static struct futex_hash_bucket *hash_futex(union futex_key *key) */ static inline int match_futex(union futex_key *key1, union futex_key *key2) { - return (key1->both.word == key2->both.word + return (key1 && key2 + && key1->both.word == key2->both.word && key1->both.ptr == key2->both.ptr && key1->both.offset == key2->both.offset); } /* - * Get parameters which are the keys for a futex. + * Take a reference to the resource addressed by a key. + * Can be called while holding spinlocks. * - * For shared mappings, it's (page->index, vma->vm_file->f_dentry->d_inode, - * offset_within_page). For private mappings, it's (uaddr, current->mm). - * We can usually work out the index without swapping in the page. + */ +static void get_futex_key_refs(union futex_key *key) +{ + if (!key->both.ptr) + return; + + switch (key->both.offset & (FUT_OFF_INODE|FUT_OFF_MMSHARED)) { + case FUT_OFF_INODE: + ihold(key->shared.inode); /* implies MB (B) */ + break; + case FUT_OFF_MMSHARED: + futex_get_mm(key); /* implies MB (B) */ + break; + } +} + +/* + * Drop a reference to the resource addressed by a key. + * The hash bucket spinlock must not be held. + */ +static void drop_futex_key_refs(union futex_key *key) +{ + if (!key->both.ptr) { + /* If we're here then we tried to put a key we failed to get */ + WARN_ON_ONCE(1); + return; + } + + switch (key->both.offset & (FUT_OFF_INODE|FUT_OFF_MMSHARED)) { + case FUT_OFF_INODE: + iput(key->shared.inode); + break; + case FUT_OFF_MMSHARED: + mmdrop(key->private.mm); + break; + } +} + +/** + * get_futex_key() - Get parameters which are the keys for a futex + * @uaddr: virtual address of the futex + * @fshared: 0 for a PROCESS_PRIVATE futex, 1 for PROCESS_SHARED + * @key: address where result is stored. + * @rw: mapping needs to be read/write (values: VERIFY_READ, + * VERIFY_WRITE) + * + * Return: a negative error code or 0 * - * Returns: 0, or negative error code. * The key words are stored in *key on success. * - * Should be called with ¤t->mm->mmap_sem but NOT any spinlocks. + * For shared mappings, it's (page->index, file_inode(vma->vm_file), + * offset_within_page). For private mappings, it's (uaddr, current->mm). + * We can usually work out the index without swapping in the page. + * + * lock_page() might sleep, the caller should not hold a spinlock. */ -static int get_futex_key(unsigned long uaddr, union futex_key *key) +static int +get_futex_key(u32 __user *uaddr, int fshared, union futex_key *key, int rw) { + unsigned long address = (unsigned long)uaddr; struct mm_struct *mm = current->mm; - struct vm_area_struct *vma; - struct page *page; - int err; + struct page *page, *page_head; + int err, ro = 0; /* * The futex address must be "naturally" aligned. */ - key->both.offset = uaddr % PAGE_SIZE; - if (unlikely((key->both.offset % sizeof(u32)) != 0)) + key->both.offset = address % PAGE_SIZE; + if (unlikely((address % sizeof(u32)) != 0)) return -EINVAL; - uaddr -= key->both.offset; + address -= key->both.offset; + + if (unlikely(!access_ok(rw, uaddr, sizeof(u32)))) + return -EFAULT; /* - * The futex is hashed differently depending on whether - * it's in a shared or private mapping. So check vma first. + * PROCESS_PRIVATE futexes are fast. + * As the mm cannot disappear under us and the 'key' only needs + * virtual address, we dont even have to find the underlying vma. + * Note : We do have to check 'uaddr' is a valid user address, + * but access_ok() should be faster than find_vma() */ - vma = find_extend_vma(mm, uaddr); - if (unlikely(!vma)) - return -EFAULT; + if (!fshared) { + key->private.mm = mm; + key->private.address = address; + get_futex_key_refs(key); /* implies MB (B) */ + return 0; + } +again: + err = get_user_pages_fast(address, 1, 1, &page); /* - * Permissions. + * If write access is not required (eg. FUTEX_WAIT), try + * and get read-only access. */ - if (unlikely((vma->vm_flags & (VM_IO|VM_READ)) != VM_READ)) - return (vma->vm_flags & VM_IO) ? -EPERM : -EACCES; + if (err == -EFAULT && rw == VERIFY_READ) { + err = get_user_pages_fast(address, 1, 0, &page); + ro = 1; + } + if (err < 0) + return err; + else + err = 0; + +#ifdef CONFIG_TRANSPARENT_HUGEPAGE + page_head = page; + if (unlikely(PageTail(page))) { + put_page(page); + /* serialize against __split_huge_page_splitting() */ + local_irq_disable(); + if (likely(__get_user_pages_fast(address, 1, !ro, &page) == 1)) { + page_head = compound_head(page); + /* + * page_head is valid pointer but we must pin + * it before taking the PG_lock and/or + * PG_compound_lock. The moment we re-enable + * irqs __split_huge_page_splitting() can + * return and the head page can be freed from + * under us. We can't take the PG_lock and/or + * PG_compound_lock on a page that could be + * freed from under us. + */ + if (page != page_head) { + get_page(page_head); + put_page(page); + } + local_irq_enable(); + } else { + local_irq_enable(); + goto again; + } + } +#else + page_head = compound_head(page); + if (page != page_head) { + get_page(page_head); + put_page(page); + } +#endif + + lock_page(page_head); + + /* + * If page_head->mapping is NULL, then it cannot be a PageAnon + * page; but it might be the ZERO_PAGE or in the gate area or + * in a special mapping (all cases which we are happy to fail); + * or it may have been a good file page when get_user_pages_fast + * found it, but truncated or holepunched or subjected to + * invalidate_complete_page2 before we got the page lock (also + * cases which we are happy to fail). And we hold a reference, + * so refcount care in invalidate_complete_page's remove_mapping + * prevents drop_caches from setting mapping to NULL beneath us. + * + * The case we do have to guard against is when memory pressure made + * shmem_writepage move it from filecache to swapcache beneath us: + * an unlikely race, but we do need to retry for page_head->mapping. + */ + if (!page_head->mapping) { + int shmem_swizzled = PageSwapCache(page_head); + unlock_page(page_head); + put_page(page_head); + if (shmem_swizzled) + goto again; + return -EFAULT; + } /* * Private mappings are handled in a simple way. * * NOTE: When userspace waits on a MAP_SHARED mapping, even if * it's a read-only handle, it's expected that futexes attach to - * the object not the particular process. Therefore we use - * VM_MAYSHARE here, not VM_SHARED which is restricted to shared - * mappings of _writable_ handles. + * the object not the particular process. */ - if (likely(!(vma->vm_flags & VM_MAYSHARE))) { + if (PageAnon(page_head)) { + /* + * A RO anonymous page will never change and thus doesn't make + * sense for futex operations. + */ + if (ro) { + err = -EFAULT; + goto out; + } + + key->both.offset |= FUT_OFF_MMSHARED; /* ref taken on mm */ key->private.mm = mm; - key->private.uaddr = uaddr; - return 0; + key->private.address = address; + } else { + key->both.offset |= FUT_OFF_INODE; /* inode-based key */ + key->shared.inode = page_head->mapping->host; + key->shared.pgoff = basepage_index(page); + } + + get_futex_key_refs(key); /* implies MB (B) */ + +out: + unlock_page(page_head); + put_page(page_head); + return err; +} + +static inline void put_futex_key(union futex_key *key) +{ + drop_futex_key_refs(key); +} + +/** + * fault_in_user_writeable() - Fault in user address and verify RW access + * @uaddr: pointer to faulting user space address + * + * Slow path to fixup the fault we just took in the atomic write + * access to @uaddr. + * + * We have no generic implementation of a non-destructive write to the + * user address. We know that we faulted in the atomic pagefault + * disabled section so we can as well avoid the #PF overhead by + * calling get_user_pages() right away. + */ +static int fault_in_user_writeable(u32 __user *uaddr) +{ + struct mm_struct *mm = current->mm; + int ret; + + down_read(&mm->mmap_sem); + ret = fixup_user_fault(current, mm, (unsigned long)uaddr, + FAULT_FLAG_WRITE); + up_read(&mm->mmap_sem); + + return ret < 0 ? ret : 0; +} + +/** + * futex_top_waiter() - Return the highest priority waiter on a futex + * @hb: the hash bucket the futex_q's reside in + * @key: the futex key (to distinguish it from other futex futex_q's) + * + * Must be called with the hb lock held. + */ +static struct futex_q *futex_top_waiter(struct futex_hash_bucket *hb, + union futex_key *key) +{ + struct futex_q *this; + + plist_for_each_entry(this, &hb->chain, list) { + if (match_futex(&this->key, key)) + return this; } + return NULL; +} + +static int cmpxchg_futex_value_locked(u32 *curval, u32 __user *uaddr, + u32 uval, u32 newval) +{ + int ret; + + pagefault_disable(); + ret = futex_atomic_cmpxchg_inatomic(curval, uaddr, uval, newval); + pagefault_enable(); + + return ret; +} + +static int get_futex_value_locked(u32 *dest, u32 __user *from) +{ + int ret; + + pagefault_disable(); + ret = __copy_from_user_inatomic(dest, from, sizeof(u32)); + pagefault_enable(); + + return ret ? -EFAULT : 0; +} + + +/* + * PI code: + */ +static int refill_pi_state_cache(void) +{ + struct futex_pi_state *pi_state; + + if (likely(current->pi_state_cache)) + return 0; + + pi_state = kzalloc(sizeof(*pi_state), GFP_KERNEL); + + if (!pi_state) + return -ENOMEM; + + INIT_LIST_HEAD(&pi_state->list); + /* pi_mutex gets initialized later */ + pi_state->owner = NULL; + atomic_set(&pi_state->refcount, 1); + pi_state->key = FUTEX_KEY_INIT; + + current->pi_state_cache = pi_state; + + return 0; +} + +static struct futex_pi_state * alloc_pi_state(void) +{ + struct futex_pi_state *pi_state = current->pi_state_cache; + + WARN_ON(!pi_state); + current->pi_state_cache = NULL; + + return pi_state; +} + +static void free_pi_state(struct futex_pi_state *pi_state) +{ + if (!atomic_dec_and_test(&pi_state->refcount)) + return; /* - * Linear file mappings are also simple. + * If pi_state->owner is NULL, the owner is most probably dying + * and has cleaned up the pi_state already */ - key->shared.inode = vma->vm_file->f_dentry->d_inode; - key->both.offset++; /* Bit 0 of offset indicates inode-based key. */ - if (likely(!(vma->vm_flags & VM_NONLINEAR))) { - key->shared.pgoff = (((uaddr - vma->vm_start) >> PAGE_SHIFT) - + vma->vm_pgoff); - return 0; + if (pi_state->owner) { + raw_spin_lock_irq(&pi_state->owner->pi_lock); + list_del_init(&pi_state->list); + raw_spin_unlock_irq(&pi_state->owner->pi_lock); + + rt_mutex_proxy_unlock(&pi_state->pi_mutex, pi_state->owner); + } + + if (current->pi_state_cache) + kfree(pi_state); + else { + /* + * pi_state->list is already empty. + * clear pi_state->owner. + * refcount is at 0 - put it back to 1. + */ + pi_state->owner = NULL; + atomic_set(&pi_state->refcount, 1); + current->pi_state_cache = pi_state; } +} + +/* + * Look up the task based on what TID userspace gave us. + * We dont trust it. + */ +static struct task_struct * futex_find_get_task(pid_t pid) +{ + struct task_struct *p; + rcu_read_lock(); + p = find_task_by_vpid(pid); + if (p) + get_task_struct(p); + + rcu_read_unlock(); + + return p; +} + +/* + * This task is holding PI mutexes at exit time => bad. + * Kernel cleans up PI-state, but userspace is likely hosed. + * (Robust-futex cleanup is separate and might save the day for userspace.) + */ +void exit_pi_state_list(struct task_struct *curr) +{ + struct list_head *next, *head = &curr->pi_state_list; + struct futex_pi_state *pi_state; + struct futex_hash_bucket *hb; + union futex_key key = FUTEX_KEY_INIT; + + if (!futex_cmpxchg_enabled) + return; /* - * We could walk the page table to read the non-linear - * pte, and get the page index without fetching the page - * from swap. But that's a lot of code to duplicate here - * for a rare case, so we simply fetch the page. + * We are a ZOMBIE and nobody can enqueue itself on + * pi_state_list anymore, but we have to be careful + * versus waiters unqueueing themselves: */ - err = get_user_pages(current, mm, uaddr, 1, 0, 0, &page, NULL); - if (err >= 0) { - key->shared.pgoff = - page->index << (PAGE_CACHE_SHIFT - PAGE_SHIFT); - put_page(page); - return 0; + raw_spin_lock_irq(&curr->pi_lock); + while (!list_empty(head)) { + + next = head->next; + pi_state = list_entry(next, struct futex_pi_state, list); + key = pi_state->key; + hb = hash_futex(&key); + raw_spin_unlock_irq(&curr->pi_lock); + + spin_lock(&hb->lock); + + raw_spin_lock_irq(&curr->pi_lock); + /* + * We dropped the pi-lock, so re-check whether this + * task still owns the PI-state: + */ + if (head->next != next) { + spin_unlock(&hb->lock); + continue; + } + + WARN_ON(pi_state->owner != curr); + WARN_ON(list_empty(&pi_state->list)); + list_del_init(&pi_state->list); + pi_state->owner = NULL; + raw_spin_unlock_irq(&curr->pi_lock); + + rt_mutex_unlock(&pi_state->pi_mutex); + + spin_unlock(&hb->lock); + + raw_spin_lock_irq(&curr->pi_lock); } - return err; + raw_spin_unlock_irq(&curr->pi_lock); } /* - * Take a reference to the resource addressed by a key. - * Can be called while holding spinlocks. + * We need to check the following states: + * + * Waiter | pi_state | pi->owner | uTID | uODIED | ? + * + * [1] NULL | --- | --- | 0 | 0/1 | Valid + * [2] NULL | --- | --- | >0 | 0/1 | Valid + * + * [3] Found | NULL | -- | Any | 0/1 | Invalid + * + * [4] Found | Found | NULL | 0 | 1 | Valid + * [5] Found | Found | NULL | >0 | 1 | Invalid * - * NOTE: mmap_sem MUST be held between get_futex_key() and calling this - * function, if it is called at all. mmap_sem keeps key->shared.inode valid. + * [6] Found | Found | task | 0 | 1 | Valid + * + * [7] Found | Found | NULL | Any | 0 | Invalid + * + * [8] Found | Found | task | ==taskTID | 0/1 | Valid + * [9] Found | Found | task | 0 | 0 | Invalid + * [10] Found | Found | task | !=taskTID | 0/1 | Invalid + * + * [1] Indicates that the kernel can acquire the futex atomically. We + * came came here due to a stale FUTEX_WAITERS/FUTEX_OWNER_DIED bit. + * + * [2] Valid, if TID does not belong to a kernel thread. If no matching + * thread is found then it indicates that the owner TID has died. + * + * [3] Invalid. The waiter is queued on a non PI futex + * + * [4] Valid state after exit_robust_list(), which sets the user space + * value to FUTEX_WAITERS | FUTEX_OWNER_DIED. + * + * [5] The user space value got manipulated between exit_robust_list() + * and exit_pi_state_list() + * + * [6] Valid state after exit_pi_state_list() which sets the new owner in + * the pi_state but cannot access the user space value. + * + * [7] pi_state->owner can only be NULL when the OWNER_DIED bit is set. + * + * [8] Owner and user space value match + * + * [9] There is no transient state which sets the user space TID to 0 + * except exit_robust_list(), but this is indicated by the + * FUTEX_OWNER_DIED bit. See [4] + * + * [10] There is no transient state which leaves owner and user space + * TID out of sync. */ -static inline void get_key_refs(union futex_key *key) +static int +lookup_pi_state(u32 uval, struct futex_hash_bucket *hb, + union futex_key *key, struct futex_pi_state **ps) { - if (key->both.ptr != 0) { - if (key->both.offset & 1) - atomic_inc(&key->shared.inode->i_count); - else - atomic_inc(&key->private.mm->mm_count); + struct futex_pi_state *pi_state = NULL; + struct futex_q *this, *next; + struct task_struct *p; + pid_t pid = uval & FUTEX_TID_MASK; + + plist_for_each_entry_safe(this, next, &hb->chain, list) { + if (match_futex(&this->key, key)) { + /* + * Sanity check the waiter before increasing + * the refcount and attaching to it. + */ + pi_state = this->pi_state; + /* + * Userspace might have messed up non-PI and + * PI futexes [3] + */ + if (unlikely(!pi_state)) + return -EINVAL; + + WARN_ON(!atomic_read(&pi_state->refcount)); + + /* + * Handle the owner died case: + */ + if (uval & FUTEX_OWNER_DIED) { + /* + * exit_pi_state_list sets owner to NULL and + * wakes the topmost waiter. The task which + * acquires the pi_state->rt_mutex will fixup + * owner. + */ + if (!pi_state->owner) { + /* + * No pi state owner, but the user + * space TID is not 0. Inconsistent + * state. [5] + */ + if (pid) + return -EINVAL; + /* + * Take a ref on the state and + * return. [4] + */ + goto out_state; + } + + /* + * If TID is 0, then either the dying owner + * has not yet executed exit_pi_state_list() + * or some waiter acquired the rtmutex in the + * pi state, but did not yet fixup the TID in + * user space. + * + * Take a ref on the state and return. [6] + */ + if (!pid) + goto out_state; + } else { + /* + * If the owner died bit is not set, + * then the pi_state must have an + * owner. [7] + */ + if (!pi_state->owner) + return -EINVAL; + } + + /* + * Bail out if user space manipulated the + * futex value. If pi state exists then the + * owner TID must be the same as the user + * space TID. [9/10] + */ + if (pid != task_pid_vnr(pi_state->owner)) + return -EINVAL; + + out_state: + atomic_inc(&pi_state->refcount); + *ps = pi_state; + return 0; + } + } + + /* + * We are the first waiter - try to look up the real owner and attach + * the new pi_state to it, but bail out when TID = 0 [1] + */ + if (!pid) + return -ESRCH; + p = futex_find_get_task(pid); + if (!p) + return -ESRCH; + + if (!p->mm) { + put_task_struct(p); + return -EPERM; + } + + /* + * We need to look at the task state flags to figure out, + * whether the task is exiting. To protect against the do_exit + * change of the task flags, we do this protected by + * p->pi_lock: + */ + raw_spin_lock_irq(&p->pi_lock); + if (unlikely(p->flags & PF_EXITING)) { + /* + * The task is on the way out. When PF_EXITPIDONE is + * set, we know that the task has finished the + * cleanup: + */ + int ret = (p->flags & PF_EXITPIDONE) ? -ESRCH : -EAGAIN; + + raw_spin_unlock_irq(&p->pi_lock); + put_task_struct(p); + return ret; } + + /* + * No existing pi state. First waiter. [2] + */ + pi_state = alloc_pi_state(); + + /* + * Initialize the pi_mutex in locked state and make 'p' + * the owner of it: + */ + rt_mutex_init_proxy_locked(&pi_state->pi_mutex, p); + + /* Store the key for possible exit cleanups: */ + pi_state->key = *key; + + WARN_ON(!list_empty(&pi_state->list)); + list_add(&pi_state->list, &p->pi_state_list); + pi_state->owner = p; + raw_spin_unlock_irq(&p->pi_lock); + + put_task_struct(p); + + *ps = pi_state; + + return 0; } -/* - * Drop a reference to the resource addressed by a key. - * The hash bucket spinlock must not be held. +/** + * futex_lock_pi_atomic() - Atomic work required to acquire a pi aware futex + * @uaddr: the pi futex user address + * @hb: the pi futex hash bucket + * @key: the futex key associated with uaddr and hb + * @ps: the pi_state pointer where we store the result of the + * lookup + * @task: the task to perform the atomic lock work for. This will + * be "current" except in the case of requeue pi. + * @set_waiters: force setting the FUTEX_WAITERS bit (1) or not (0) + * + * Return: + * 0 - ready to wait; + * 1 - acquired the lock; + * <0 - error + * + * The hb->lock and futex_key refs shall be held by the caller. */ -static void drop_key_refs(union futex_key *key) +static int futex_lock_pi_atomic(u32 __user *uaddr, struct futex_hash_bucket *hb, + union futex_key *key, + struct futex_pi_state **ps, + struct task_struct *task, int set_waiters) { - if (key->both.ptr != 0) { - if (key->both.offset & 1) - iput(key->shared.inode); - else - mmdrop(key->private.mm); + int lock_taken, ret, force_take = 0; + u32 uval, newval, curval, vpid = task_pid_vnr(task); + +retry: + ret = lock_taken = 0; + + /* + * To avoid races, we attempt to take the lock here again + * (by doing a 0 -> TID atomic cmpxchg), while holding all + * the locks. It will most likely not succeed. + */ + newval = vpid; + if (set_waiters) + newval |= FUTEX_WAITERS; + + if (unlikely(cmpxchg_futex_value_locked(&curval, uaddr, 0, newval))) + return -EFAULT; + + /* + * Detect deadlocks. + */ + if ((unlikely((curval & FUTEX_TID_MASK) == vpid))) + return -EDEADLK; + + /* + * Surprise - we got the lock, but we do not trust user space at all. + */ + if (unlikely(!curval)) { + /* + * We verify whether there is kernel state for this + * futex. If not, we can safely assume, that the 0 -> + * TID transition is correct. If state exists, we do + * not bother to fixup the user space state as it was + * corrupted already. + */ + return futex_top_waiter(hb, key) ? -EINVAL : 1; + } + + uval = curval; + + /* + * Set the FUTEX_WAITERS flag, so the owner will know it has someone + * to wake at the next unlock. + */ + newval = curval | FUTEX_WAITERS; + + /* + * Should we force take the futex? See below. + */ + if (unlikely(force_take)) { + /* + * Keep the OWNER_DIED and the WAITERS bit and set the + * new TID value. + */ + newval = (curval & ~FUTEX_TID_MASK) | vpid; + force_take = 0; + lock_taken = 1; + } + + if (unlikely(cmpxchg_futex_value_locked(&curval, uaddr, uval, newval))) + return -EFAULT; + if (unlikely(curval != uval)) + goto retry; + + /* + * We took the lock due to forced take over. + */ + if (unlikely(lock_taken)) + return 1; + + /* + * We dont have the lock. Look up the PI state (or create it if + * we are the first waiter): + */ + ret = lookup_pi_state(uval, hb, key, ps); + + if (unlikely(ret)) { + switch (ret) { + case -ESRCH: + /* + * We failed to find an owner for this + * futex. So we have no pi_state to block + * on. This can happen in two cases: + * + * 1) The owner died + * 2) A stale FUTEX_WAITERS bit + * + * Re-read the futex value. + */ + if (get_futex_value_locked(&curval, uaddr)) + return -EFAULT; + + /* + * If the owner died or we have a stale + * WAITERS bit the owner TID in the user space + * futex is 0. + */ + if (!(curval & FUTEX_TID_MASK)) { + force_take = 1; + goto retry; + } + default: + break; + } } + + return ret; } -static inline int get_futex_value_locked(int *dest, int __user *from) +/** + * __unqueue_futex() - Remove the futex_q from its futex_hash_bucket + * @q: The futex_q to unqueue + * + * The q->lock_ptr must not be NULL and must be held by the caller. + */ +static void __unqueue_futex(struct futex_q *q) { - int ret; + struct futex_hash_bucket *hb; - inc_preempt_count(); - ret = __copy_from_user_inatomic(dest, from, sizeof(int)); - dec_preempt_count(); + if (WARN_ON_SMP(!q->lock_ptr || !spin_is_locked(q->lock_ptr)) + || WARN_ON(plist_node_empty(&q->list))) + return; - return ret ? -EFAULT : 0; + hb = container_of(q->lock_ptr, struct futex_hash_bucket, lock); + plist_del(&q->list, &hb->chain); + hb_waiters_dec(hb); } /* @@ -259,60 +1097,182 @@ static inline int get_futex_value_locked(int *dest, int __user *from) */ static void wake_futex(struct futex_q *q) { - list_del_init(&q->list); - if (q->filp) - send_sigio(&q->filp->f_owner, q->fd, POLL_IN); + struct task_struct *p = q->task; + + if (WARN(q->pi_state || q->rt_waiter, "refusing to wake PI futex\n")) + return; + /* - * The lock in wake_up_all() is a crucial memory barrier after the - * list_del_init() and also before assigning to q->lock_ptr. + * We set q->lock_ptr = NULL _before_ we wake up the task. If + * a non-futex wake up happens on another CPU then the task + * might exit and p would dereference a non-existing task + * struct. Prevent this by holding a reference on p across the + * wake up. */ - wake_up_all(&q->waiters); + get_task_struct(p); + + __unqueue_futex(q); /* - * The waiting task can free the futex_q as soon as this is written, - * without taking any locks. This must come last. - * - * A memory barrier is required here to prevent the following store - * to lock_ptr from getting ahead of the wakeup. Clearing the lock - * at the end of wake_up_all() does not prevent this store from - * moving. + * The waiting task can free the futex_q as soon as + * q->lock_ptr = NULL is written, without taking any locks. A + * memory barrier is required here to prevent the following + * store to lock_ptr from getting ahead of the plist_del. */ - wmb(); + smp_wmb(); q->lock_ptr = NULL; + + wake_up_state(p, TASK_NORMAL); + put_task_struct(p); +} + +static int wake_futex_pi(u32 __user *uaddr, u32 uval, struct futex_q *this) +{ + struct task_struct *new_owner; + struct futex_pi_state *pi_state = this->pi_state; + u32 uninitialized_var(curval), newval; + int ret = 0; + + if (!pi_state) + return -EINVAL; + + /* + * If current does not own the pi_state then the futex is + * inconsistent and user space fiddled with the futex value. + */ + if (pi_state->owner != current) + return -EINVAL; + + raw_spin_lock(&pi_state->pi_mutex.wait_lock); + new_owner = rt_mutex_next_owner(&pi_state->pi_mutex); + + /* + * It is possible that the next waiter (the one that brought + * this owner to the kernel) timed out and is no longer + * waiting on the lock. + */ + if (!new_owner) + new_owner = this->task; + + /* + * We pass it to the next owner. The WAITERS bit is always + * kept enabled while there is PI state around. We cleanup the + * owner died bit, because we are the owner. + */ + newval = FUTEX_WAITERS | task_pid_vnr(new_owner); + + if (cmpxchg_futex_value_locked(&curval, uaddr, uval, newval)) + ret = -EFAULT; + else if (curval != uval) + ret = -EINVAL; + if (ret) { + raw_spin_unlock(&pi_state->pi_mutex.wait_lock); + return ret; + } + + raw_spin_lock_irq(&pi_state->owner->pi_lock); + WARN_ON(list_empty(&pi_state->list)); + list_del_init(&pi_state->list); + raw_spin_unlock_irq(&pi_state->owner->pi_lock); + + raw_spin_lock_irq(&new_owner->pi_lock); + WARN_ON(!list_empty(&pi_state->list)); + list_add(&pi_state->list, &new_owner->pi_state_list); + pi_state->owner = new_owner; + raw_spin_unlock_irq(&new_owner->pi_lock); + + raw_spin_unlock(&pi_state->pi_mutex.wait_lock); + rt_mutex_unlock(&pi_state->pi_mutex); + + return 0; +} + +static int unlock_futex_pi(u32 __user *uaddr, u32 uval) +{ + u32 uninitialized_var(oldval); + + /* + * There is no waiter, so we unlock the futex. The owner died + * bit has not to be preserved here. We are the owner: + */ + if (cmpxchg_futex_value_locked(&oldval, uaddr, uval, 0)) + return -EFAULT; + if (oldval != uval) + return -EAGAIN; + + return 0; } /* - * Wake up all waiters hashed on the physical page that is mapped - * to this virtual address: + * Express the locking dependencies for lockdep: */ -static int futex_wake(unsigned long uaddr, int nr_wake) +static inline void +double_lock_hb(struct futex_hash_bucket *hb1, struct futex_hash_bucket *hb2) { - union futex_key key; - struct futex_hash_bucket *bh; - struct list_head *head; + if (hb1 <= hb2) { + spin_lock(&hb1->lock); + if (hb1 < hb2) + spin_lock_nested(&hb2->lock, SINGLE_DEPTH_NESTING); + } else { /* hb1 > hb2 */ + spin_lock(&hb2->lock); + spin_lock_nested(&hb1->lock, SINGLE_DEPTH_NESTING); + } +} + +static inline void +double_unlock_hb(struct futex_hash_bucket *hb1, struct futex_hash_bucket *hb2) +{ + spin_unlock(&hb1->lock); + if (hb1 != hb2) + spin_unlock(&hb2->lock); +} + +/* + * Wake up waiters matching bitset queued on this futex (uaddr). + */ +static int +futex_wake(u32 __user *uaddr, unsigned int flags, int nr_wake, u32 bitset) +{ + struct futex_hash_bucket *hb; struct futex_q *this, *next; + union futex_key key = FUTEX_KEY_INIT; int ret; - down_read(¤t->mm->mmap_sem); + if (!bitset) + return -EINVAL; - ret = get_futex_key(uaddr, &key); + ret = get_futex_key(uaddr, flags & FLAGS_SHARED, &key, VERIFY_READ); if (unlikely(ret != 0)) goto out; - bh = hash_futex(&key); - spin_lock(&bh->lock); - head = &bh->chain; + hb = hash_futex(&key); + + /* Make sure we really have tasks to wakeup */ + if (!hb_waiters_pending(hb)) + goto out_put_key; - list_for_each_entry_safe(this, next, head, list) { + spin_lock(&hb->lock); + + plist_for_each_entry_safe(this, next, &hb->chain, list) { if (match_futex (&this->key, &key)) { + if (this->pi_state || this->rt_waiter) { + ret = -EINVAL; + break; + } + + /* Check if one of the bits is set in both bitsets */ + if (!(this->bitset & bitset)) + continue; + wake_futex(this); if (++ret >= nr_wake) break; } } - spin_unlock(&bh->lock); + spin_unlock(&hb->lock); +out_put_key: + put_futex_key(&key); out: - up_read(¤t->mm->mmap_sem); return ret; } @@ -320,98 +1280,65 @@ out: * Wake up all waiters hashed on the physical page that is mapped * to this virtual address: */ -static int futex_wake_op(unsigned long uaddr1, unsigned long uaddr2, int nr_wake, int nr_wake2, int op) +static int +futex_wake_op(u32 __user *uaddr1, unsigned int flags, u32 __user *uaddr2, + int nr_wake, int nr_wake2, int op) { - union futex_key key1, key2; - struct futex_hash_bucket *bh1, *bh2; - struct list_head *head; + union futex_key key1 = FUTEX_KEY_INIT, key2 = FUTEX_KEY_INIT; + struct futex_hash_bucket *hb1, *hb2; struct futex_q *this, *next; - int ret, op_ret, attempt = 0; - -retryfull: - down_read(¤t->mm->mmap_sem); + int ret, op_ret; - ret = get_futex_key(uaddr1, &key1); +retry: + ret = get_futex_key(uaddr1, flags & FLAGS_SHARED, &key1, VERIFY_READ); if (unlikely(ret != 0)) goto out; - ret = get_futex_key(uaddr2, &key2); + ret = get_futex_key(uaddr2, flags & FLAGS_SHARED, &key2, VERIFY_WRITE); if (unlikely(ret != 0)) - goto out; - - bh1 = hash_futex(&key1); - bh2 = hash_futex(&key2); + goto out_put_key1; -retry: - if (bh1 < bh2) - spin_lock(&bh1->lock); - spin_lock(&bh2->lock); - if (bh1 > bh2) - spin_lock(&bh1->lock); + hb1 = hash_futex(&key1); + hb2 = hash_futex(&key2); - op_ret = futex_atomic_op_inuser(op, (int __user *)uaddr2); +retry_private: + double_lock_hb(hb1, hb2); + op_ret = futex_atomic_op_inuser(op, uaddr2); if (unlikely(op_ret < 0)) { - int dummy; - spin_unlock(&bh1->lock); - if (bh1 != bh2) - spin_unlock(&bh2->lock); + double_unlock_hb(hb1, hb2); #ifndef CONFIG_MMU - /* we don't get EFAULT from MMU faults if we don't have an MMU, - * but we might get them from range checking */ + /* + * we don't get EFAULT from MMU faults if we don't have an MMU, + * but we might get them from range checking + */ ret = op_ret; - goto out; + goto out_put_keys; #endif if (unlikely(op_ret != -EFAULT)) { ret = op_ret; - goto out; + goto out_put_keys; } - /* futex_atomic_op_inuser needs to both read and write - * *(int __user *)uaddr2, but we can't modify it - * non-atomically. Therefore, if get_user below is not - * enough, we need to handle the fault ourselves, while - * still holding the mmap_sem. */ - if (attempt++) { - struct vm_area_struct * vma; - struct mm_struct *mm = current->mm; - - ret = -EFAULT; - if (attempt >= 2 || - !(vma = find_vma(mm, uaddr2)) || - vma->vm_start > uaddr2 || - !(vma->vm_flags & VM_WRITE)) - goto out; - - switch (handle_mm_fault(mm, vma, uaddr2, 1)) { - case VM_FAULT_MINOR: - current->min_flt++; - break; - case VM_FAULT_MAJOR: - current->maj_flt++; - break; - default: - goto out; - } - goto retry; - } - - /* If we would have faulted, release mmap_sem, - * fault it in and start all over again. */ - up_read(¤t->mm->mmap_sem); - - ret = get_user(dummy, (int __user *)uaddr2); + ret = fault_in_user_writeable(uaddr2); if (ret) - return ret; + goto out_put_keys; - goto retryfull; - } + if (!(flags & FLAGS_SHARED)) + goto retry_private; - head = &bh1->chain; + put_futex_key(&key2); + put_futex_key(&key1); + goto retry; + } - list_for_each_entry_safe(this, next, head, list) { + plist_for_each_entry_safe(this, next, &hb1->chain, list) { if (match_futex (&this->key, &key1)) { + if (this->pi_state || this->rt_waiter) { + ret = -EINVAL; + goto out_unlock; + } wake_futex(this); if (++ret >= nr_wake) break; @@ -419,11 +1346,13 @@ retry: } if (op_ret > 0) { - head = &bh2->chain; - op_ret = 0; - list_for_each_entry_safe(this, next, head, list) { + plist_for_each_entry_safe(this, next, &hb2->chain, list) { if (match_futex (&this->key, &key2)) { + if (this->pi_state || this->rt_waiter) { + ret = -EINVAL; + goto out_unlock; + } wake_futex(this); if (++op_ret >= nr_wake2) break; @@ -432,164 +1361,489 @@ retry: ret += op_ret; } - spin_unlock(&bh1->lock); - if (bh1 != bh2) - spin_unlock(&bh2->lock); +out_unlock: + double_unlock_hb(hb1, hb2); +out_put_keys: + put_futex_key(&key2); +out_put_key1: + put_futex_key(&key1); out: - up_read(¤t->mm->mmap_sem); return ret; } -/* - * Requeue all waiters hashed on one physical page to another - * physical page. +/** + * requeue_futex() - Requeue a futex_q from one hb to another + * @q: the futex_q to requeue + * @hb1: the source hash_bucket + * @hb2: the target hash_bucket + * @key2: the new key for the requeued futex_q + */ +static inline +void requeue_futex(struct futex_q *q, struct futex_hash_bucket *hb1, + struct futex_hash_bucket *hb2, union futex_key *key2) +{ + + /* + * If key1 and key2 hash to the same bucket, no need to + * requeue. + */ + if (likely(&hb1->chain != &hb2->chain)) { + plist_del(&q->list, &hb1->chain); + hb_waiters_dec(hb1); + plist_add(&q->list, &hb2->chain); + hb_waiters_inc(hb2); + q->lock_ptr = &hb2->lock; + } + get_futex_key_refs(key2); + q->key = *key2; +} + +/** + * requeue_pi_wake_futex() - Wake a task that acquired the lock during requeue + * @q: the futex_q + * @key: the key of the requeue target futex + * @hb: the hash_bucket of the requeue target futex + * + * During futex_requeue, with requeue_pi=1, it is possible to acquire the + * target futex if it is uncontended or via a lock steal. Set the futex_q key + * to the requeue target futex so the waiter can detect the wakeup on the right + * futex, but remove it from the hb and NULL the rt_waiter so it can detect + * atomic lock acquisition. Set the q->lock_ptr to the requeue target hb->lock + * to protect access to the pi_state to fixup the owner later. Must be called + * with both q->lock_ptr and hb->lock held. + */ +static inline +void requeue_pi_wake_futex(struct futex_q *q, union futex_key *key, + struct futex_hash_bucket *hb) +{ + get_futex_key_refs(key); + q->key = *key; + + __unqueue_futex(q); + + WARN_ON(!q->rt_waiter); + q->rt_waiter = NULL; + + q->lock_ptr = &hb->lock; + + wake_up_state(q->task, TASK_NORMAL); +} + +/** + * futex_proxy_trylock_atomic() - Attempt an atomic lock for the top waiter + * @pifutex: the user address of the to futex + * @hb1: the from futex hash bucket, must be locked by the caller + * @hb2: the to futex hash bucket, must be locked by the caller + * @key1: the from futex key + * @key2: the to futex key + * @ps: address to store the pi_state pointer + * @set_waiters: force setting the FUTEX_WAITERS bit (1) or not (0) + * + * Try and get the lock on behalf of the top waiter if we can do it atomically. + * Wake the top waiter if we succeed. If the caller specified set_waiters, + * then direct futex_lock_pi_atomic() to force setting the FUTEX_WAITERS bit. + * hb1 and hb2 must be held by the caller. + * + * Return: + * 0 - failed to acquire the lock atomically; + * >0 - acquired the lock, return value is vpid of the top_waiter + * <0 - error + */ +static int futex_proxy_trylock_atomic(u32 __user *pifutex, + struct futex_hash_bucket *hb1, + struct futex_hash_bucket *hb2, + union futex_key *key1, union futex_key *key2, + struct futex_pi_state **ps, int set_waiters) +{ + struct futex_q *top_waiter = NULL; + u32 curval; + int ret, vpid; + + if (get_futex_value_locked(&curval, pifutex)) + return -EFAULT; + + /* + * Find the top_waiter and determine if there are additional waiters. + * If the caller intends to requeue more than 1 waiter to pifutex, + * force futex_lock_pi_atomic() to set the FUTEX_WAITERS bit now, + * as we have means to handle the possible fault. If not, don't set + * the bit unecessarily as it will force the subsequent unlock to enter + * the kernel. + */ + top_waiter = futex_top_waiter(hb1, key1); + + /* There are no waiters, nothing for us to do. */ + if (!top_waiter) + return 0; + + /* Ensure we requeue to the expected futex. */ + if (!match_futex(top_waiter->requeue_pi_key, key2)) + return -EINVAL; + + /* + * Try to take the lock for top_waiter. Set the FUTEX_WAITERS bit in + * the contended case or if set_waiters is 1. The pi_state is returned + * in ps in contended cases. + */ + vpid = task_pid_vnr(top_waiter->task); + ret = futex_lock_pi_atomic(pifutex, hb2, key2, ps, top_waiter->task, + set_waiters); + if (ret == 1) { + requeue_pi_wake_futex(top_waiter, key2, hb2); + return vpid; + } + return ret; +} + +/** + * futex_requeue() - Requeue waiters from uaddr1 to uaddr2 + * @uaddr1: source futex user address + * @flags: futex flags (FLAGS_SHARED, etc.) + * @uaddr2: target futex user address + * @nr_wake: number of waiters to wake (must be 1 for requeue_pi) + * @nr_requeue: number of waiters to requeue (0-INT_MAX) + * @cmpval: @uaddr1 expected value (or %NULL) + * @requeue_pi: if we are attempting to requeue from a non-pi futex to a + * pi futex (pi to pi requeue is not supported) + * + * Requeue waiters on uaddr1 to uaddr2. In the requeue_pi case, try to acquire + * uaddr2 atomically on behalf of the top waiter. + * + * Return: + * >=0 - on success, the number of tasks requeued or woken; + * <0 - on error */ -static int futex_requeue(unsigned long uaddr1, unsigned long uaddr2, - int nr_wake, int nr_requeue, int *valp) +static int futex_requeue(u32 __user *uaddr1, unsigned int flags, + u32 __user *uaddr2, int nr_wake, int nr_requeue, + u32 *cmpval, int requeue_pi) { - union futex_key key1, key2; - struct futex_hash_bucket *bh1, *bh2; - struct list_head *head1; + union futex_key key1 = FUTEX_KEY_INIT, key2 = FUTEX_KEY_INIT; + int drop_count = 0, task_count = 0, ret; + struct futex_pi_state *pi_state = NULL; + struct futex_hash_bucket *hb1, *hb2; struct futex_q *this, *next; - int ret, drop_count = 0; - retry: - down_read(¤t->mm->mmap_sem); + if (requeue_pi) { + /* + * Requeue PI only works on two distinct uaddrs. This + * check is only valid for private futexes. See below. + */ + if (uaddr1 == uaddr2) + return -EINVAL; - ret = get_futex_key(uaddr1, &key1); + /* + * requeue_pi requires a pi_state, try to allocate it now + * without any locks in case it fails. + */ + if (refill_pi_state_cache()) + return -ENOMEM; + /* + * requeue_pi must wake as many tasks as it can, up to nr_wake + * + nr_requeue, since it acquires the rt_mutex prior to + * returning to userspace, so as to not leave the rt_mutex with + * waiters and no owner. However, second and third wake-ups + * cannot be predicted as they involve race conditions with the + * first wake and a fault while looking up the pi_state. Both + * pthread_cond_signal() and pthread_cond_broadcast() should + * use nr_wake=1. + */ + if (nr_wake != 1) + return -EINVAL; + } + +retry: + if (pi_state != NULL) { + /* + * We will have to lookup the pi_state again, so free this one + * to keep the accounting correct. + */ + free_pi_state(pi_state); + pi_state = NULL; + } + + ret = get_futex_key(uaddr1, flags & FLAGS_SHARED, &key1, VERIFY_READ); if (unlikely(ret != 0)) goto out; - ret = get_futex_key(uaddr2, &key2); + ret = get_futex_key(uaddr2, flags & FLAGS_SHARED, &key2, + requeue_pi ? VERIFY_WRITE : VERIFY_READ); if (unlikely(ret != 0)) - goto out; + goto out_put_key1; - bh1 = hash_futex(&key1); - bh2 = hash_futex(&key2); + /* + * The check above which compares uaddrs is not sufficient for + * shared futexes. We need to compare the keys: + */ + if (requeue_pi && match_futex(&key1, &key2)) { + ret = -EINVAL; + goto out_put_keys; + } - if (bh1 < bh2) - spin_lock(&bh1->lock); - spin_lock(&bh2->lock); - if (bh1 > bh2) - spin_lock(&bh1->lock); + hb1 = hash_futex(&key1); + hb2 = hash_futex(&key2); - if (likely(valp != NULL)) { - int curval; +retry_private: + hb_waiters_inc(hb2); + double_lock_hb(hb1, hb2); - ret = get_futex_value_locked(&curval, (int __user *)uaddr1); + if (likely(cmpval != NULL)) { + u32 curval; - if (unlikely(ret)) { - spin_unlock(&bh1->lock); - if (bh1 != bh2) - spin_unlock(&bh2->lock); + ret = get_futex_value_locked(&curval, uaddr1); - /* If we would have faulted, release mmap_sem, fault - * it in and start all over again. - */ - up_read(¤t->mm->mmap_sem); + if (unlikely(ret)) { + double_unlock_hb(hb1, hb2); + hb_waiters_dec(hb2); - ret = get_user(curval, (int __user *)uaddr1); + ret = get_user(curval, uaddr1); + if (ret) + goto out_put_keys; - if (!ret) - goto retry; + if (!(flags & FLAGS_SHARED)) + goto retry_private; - return ret; + put_futex_key(&key2); + put_futex_key(&key1); + goto retry; } - if (curval != *valp) { + if (curval != *cmpval) { ret = -EAGAIN; goto out_unlock; } } - head1 = &bh1->chain; - list_for_each_entry_safe(this, next, head1, list) { - if (!match_futex (&this->key, &key1)) + if (requeue_pi && (task_count - nr_wake < nr_requeue)) { + /* + * Attempt to acquire uaddr2 and wake the top waiter. If we + * intend to requeue waiters, force setting the FUTEX_WAITERS + * bit. We force this here where we are able to easily handle + * faults rather in the requeue loop below. + */ + ret = futex_proxy_trylock_atomic(uaddr2, hb1, hb2, &key1, + &key2, &pi_state, nr_requeue); + + /* + * At this point the top_waiter has either taken uaddr2 or is + * waiting on it. If the former, then the pi_state will not + * exist yet, look it up one more time to ensure we have a + * reference to it. If the lock was taken, ret contains the + * vpid of the top waiter task. + */ + if (ret > 0) { + WARN_ON(pi_state); + drop_count++; + task_count++; + /* + * If we acquired the lock, then the user + * space value of uaddr2 should be vpid. It + * cannot be changed by the top waiter as it + * is blocked on hb2 lock if it tries to do + * so. If something fiddled with it behind our + * back the pi state lookup might unearth + * it. So we rather use the known value than + * rereading and handing potential crap to + * lookup_pi_state. + */ + ret = lookup_pi_state(ret, hb2, &key2, &pi_state); + } + + switch (ret) { + case 0: + break; + case -EFAULT: + double_unlock_hb(hb1, hb2); + hb_waiters_dec(hb2); + put_futex_key(&key2); + put_futex_key(&key1); + ret = fault_in_user_writeable(uaddr2); + if (!ret) + goto retry; + goto out; + case -EAGAIN: + /* The owner was exiting, try again. */ + double_unlock_hb(hb1, hb2); + hb_waiters_dec(hb2); + put_futex_key(&key2); + put_futex_key(&key1); + cond_resched(); + goto retry; + default: + goto out_unlock; + } + } + + plist_for_each_entry_safe(this, next, &hb1->chain, list) { + if (task_count - nr_wake >= nr_requeue) + break; + + if (!match_futex(&this->key, &key1)) continue; - if (++ret <= nr_wake) { + + /* + * FUTEX_WAIT_REQEUE_PI and FUTEX_CMP_REQUEUE_PI should always + * be paired with each other and no other futex ops. + * + * We should never be requeueing a futex_q with a pi_state, + * which is awaiting a futex_unlock_pi(). + */ + if ((requeue_pi && !this->rt_waiter) || + (!requeue_pi && this->rt_waiter) || + this->pi_state) { + ret = -EINVAL; + break; + } + + /* + * Wake nr_wake waiters. For requeue_pi, if we acquired the + * lock, we already woke the top_waiter. If not, it will be + * woken by futex_unlock_pi(). + */ + if (++task_count <= nr_wake && !requeue_pi) { wake_futex(this); - } else { - list_move_tail(&this->list, &bh2->chain); - this->lock_ptr = &bh2->lock; - this->key = key2; - get_key_refs(&key2); - drop_count++; + continue; + } - if (ret - nr_wake >= nr_requeue) - break; - /* Make sure to stop if key1 == key2 */ - if (head1 == &bh2->chain && head1 != &next->list) - head1 = &this->list; + /* Ensure we requeue to the expected futex for requeue_pi. */ + if (requeue_pi && !match_futex(this->requeue_pi_key, &key2)) { + ret = -EINVAL; + break; } + + /* + * Requeue nr_requeue waiters and possibly one more in the case + * of requeue_pi if we couldn't acquire the lock atomically. + */ + if (requeue_pi) { + /* Prepare the waiter to take the rt_mutex. */ + atomic_inc(&pi_state->refcount); + this->pi_state = pi_state; + ret = rt_mutex_start_proxy_lock(&pi_state->pi_mutex, + this->rt_waiter, + this->task, 1); + if (ret == 1) { + /* We got the lock. */ + requeue_pi_wake_futex(this, &key2, hb2); + drop_count++; + continue; + } else if (ret) { + /* -EDEADLK */ + this->pi_state = NULL; + free_pi_state(pi_state); + goto out_unlock; + } + } + requeue_futex(this, hb1, hb2, &key2); + drop_count++; } out_unlock: - spin_unlock(&bh1->lock); - if (bh1 != bh2) - spin_unlock(&bh2->lock); + double_unlock_hb(hb1, hb2); + hb_waiters_dec(hb2); - /* drop_key_refs() must be called outside the spinlocks. */ + /* + * drop_futex_key_refs() must be called outside the spinlocks. During + * the requeue we moved futex_q's from the hash bucket at key1 to the + * one at key2 and updated their key pointer. We no longer need to + * hold the references to key1. + */ while (--drop_count >= 0) - drop_key_refs(&key1); + drop_futex_key_refs(&key1); +out_put_keys: + put_futex_key(&key2); +out_put_key1: + put_futex_key(&key1); out: - up_read(¤t->mm->mmap_sem); - return ret; + if (pi_state != NULL) + free_pi_state(pi_state); + return ret ? ret : task_count; } /* The key must be already stored in q->key. */ -static inline struct futex_hash_bucket * -queue_lock(struct futex_q *q, int fd, struct file *filp) +static inline struct futex_hash_bucket *queue_lock(struct futex_q *q) + __acquires(&hb->lock) { - struct futex_hash_bucket *bh; + struct futex_hash_bucket *hb; - q->fd = fd; - q->filp = filp; + hb = hash_futex(&q->key); - init_waitqueue_head(&q->waiters); - - get_key_refs(&q->key); - bh = hash_futex(&q->key); - q->lock_ptr = &bh->lock; + /* + * Increment the counter before taking the lock so that + * a potential waker won't miss a to-be-slept task that is + * waiting for the spinlock. This is safe as all queue_lock() + * users end up calling queue_me(). Similarly, for housekeeping, + * decrement the counter at queue_unlock() when some error has + * occurred and we don't end up adding the task to the list. + */ + hb_waiters_inc(hb); - spin_lock(&bh->lock); - return bh; -} + q->lock_ptr = &hb->lock; -static inline void __queue_me(struct futex_q *q, struct futex_hash_bucket *bh) -{ - list_add_tail(&q->list, &bh->chain); - spin_unlock(&bh->lock); + spin_lock(&hb->lock); /* implies MB (A) */ + return hb; } static inline void -queue_unlock(struct futex_q *q, struct futex_hash_bucket *bh) +queue_unlock(struct futex_hash_bucket *hb) + __releases(&hb->lock) { - spin_unlock(&bh->lock); - drop_key_refs(&q->key); + spin_unlock(&hb->lock); + hb_waiters_dec(hb); } -/* - * queue_me and unqueue_me must be called as a pair, each - * exactly once. They are called with the hashed spinlock held. +/** + * queue_me() - Enqueue the futex_q on the futex_hash_bucket + * @q: The futex_q to enqueue + * @hb: The destination hash bucket + * + * The hb->lock must be held by the caller, and is released here. A call to + * queue_me() is typically paired with exactly one call to unqueue_me(). The + * exceptions involve the PI related operations, which may use unqueue_me_pi() + * or nothing if the unqueue is done as part of the wake process and the unqueue + * state is implicit in the state of woken task (see futex_wait_requeue_pi() for + * an example). */ - -/* The key must be already stored in q->key. */ -static void queue_me(struct futex_q *q, int fd, struct file *filp) +static inline void queue_me(struct futex_q *q, struct futex_hash_bucket *hb) + __releases(&hb->lock) { - struct futex_hash_bucket *bh; - bh = queue_lock(q, fd, filp); - __queue_me(q, bh); + int prio; + + /* + * The priority used to register this element is + * - either the real thread-priority for the real-time threads + * (i.e. threads with a priority lower than MAX_RT_PRIO) + * - or MAX_RT_PRIO for non-RT threads. + * Thus, all RT-threads are woken first in priority order, and + * the others are woken last, in FIFO order. + */ + prio = min(current->normal_prio, MAX_RT_PRIO); + + plist_node_init(&q->list, prio); + plist_add(&q->list, &hb->chain); + q->task = current; + spin_unlock(&hb->lock); } -/* Return 1 if we were still queued (ie. 0 means we were woken) */ +/** + * unqueue_me() - Remove the futex_q from its futex_hash_bucket + * @q: The futex_q to unqueue + * + * The q->lock_ptr must not be held by the caller. A call to unqueue_me() must + * be paired with exactly one earlier call to queue_me(). + * + * Return: + * 1 - if the futex_q was still queued (and we removed unqueued it); + * 0 - if the futex_q was already removed by the waking thread + */ static int unqueue_me(struct futex_q *q) { - int ret = 0; spinlock_t *lock_ptr; + int ret = 0; /* In the common case we don't take the spinlock, which is nice. */ - retry: +retry: lock_ptr = q->lock_ptr; - if (lock_ptr != 0) { + barrier(); + if (lock_ptr != NULL) { spin_lock(lock_ptr); /* * q->lock_ptr can change between reading it and @@ -608,34 +1862,274 @@ static int unqueue_me(struct futex_q *q) spin_unlock(lock_ptr); goto retry; } - WARN_ON(list_empty(&q->list)); - list_del(&q->list); + __unqueue_futex(q); + + BUG_ON(q->pi_state); + spin_unlock(lock_ptr); ret = 1; } - drop_key_refs(&q->key); + drop_futex_key_refs(&q->key); return ret; } -static int futex_wait(unsigned long uaddr, int val, unsigned long time) +/* + * PI futexes can not be requeued and must remove themself from the + * hash bucket. The hash bucket lock (i.e. lock_ptr) is held on entry + * and dropped here. + */ +static void unqueue_me_pi(struct futex_q *q) + __releases(q->lock_ptr) { - DECLARE_WAITQUEUE(wait, current); - int ret, curval; - struct futex_q q; - struct futex_hash_bucket *bh; + __unqueue_futex(q); - retry: - down_read(¤t->mm->mmap_sem); + BUG_ON(!q->pi_state); + free_pi_state(q->pi_state); + q->pi_state = NULL; - ret = get_futex_key(uaddr, &q.key); - if (unlikely(ret != 0)) - goto out_release_sem; + spin_unlock(q->lock_ptr); +} + +/* + * Fixup the pi_state owner with the new owner. + * + * Must be called with hash bucket lock held and mm->sem held for non + * private futexes. + */ +static int fixup_pi_state_owner(u32 __user *uaddr, struct futex_q *q, + struct task_struct *newowner) +{ + u32 newtid = task_pid_vnr(newowner) | FUTEX_WAITERS; + struct futex_pi_state *pi_state = q->pi_state; + struct task_struct *oldowner = pi_state->owner; + u32 uval, uninitialized_var(curval), newval; + int ret; + + /* Owner died? */ + if (!pi_state->owner) + newtid |= FUTEX_OWNER_DIED; + + /* + * We are here either because we stole the rtmutex from the + * previous highest priority waiter or we are the highest priority + * waiter but failed to get the rtmutex the first time. + * We have to replace the newowner TID in the user space variable. + * This must be atomic as we have to preserve the owner died bit here. + * + * Note: We write the user space value _before_ changing the pi_state + * because we can fault here. Imagine swapped out pages or a fork + * that marked all the anonymous memory readonly for cow. + * + * Modifying pi_state _before_ the user space value would + * leave the pi_state in an inconsistent state when we fault + * here, because we need to drop the hash bucket lock to + * handle the fault. This might be observed in the PID check + * in lookup_pi_state. + */ +retry: + if (get_futex_value_locked(&uval, uaddr)) + goto handle_fault; + + while (1) { + newval = (uval & FUTEX_OWNER_DIED) | newtid; + + if (cmpxchg_futex_value_locked(&curval, uaddr, uval, newval)) + goto handle_fault; + if (curval == uval) + break; + uval = curval; + } + + /* + * We fixed up user space. Now we need to fix the pi_state + * itself. + */ + if (pi_state->owner != NULL) { + raw_spin_lock_irq(&pi_state->owner->pi_lock); + WARN_ON(list_empty(&pi_state->list)); + list_del_init(&pi_state->list); + raw_spin_unlock_irq(&pi_state->owner->pi_lock); + } + + pi_state->owner = newowner; + + raw_spin_lock_irq(&newowner->pi_lock); + WARN_ON(!list_empty(&pi_state->list)); + list_add(&pi_state->list, &newowner->pi_state_list); + raw_spin_unlock_irq(&newowner->pi_lock); + return 0; + + /* + * To handle the page fault we need to drop the hash bucket + * lock here. That gives the other task (either the highest priority + * waiter itself or the task which stole the rtmutex) the + * chance to try the fixup of the pi_state. So once we are + * back from handling the fault we need to check the pi_state + * after reacquiring the hash bucket lock and before trying to + * do another fixup. When the fixup has been done already we + * simply return. + */ +handle_fault: + spin_unlock(q->lock_ptr); + + ret = fault_in_user_writeable(uaddr); + + spin_lock(q->lock_ptr); + + /* + * Check if someone else fixed it for us: + */ + if (pi_state->owner != oldowner) + return 0; + + if (ret) + return ret; + + goto retry; +} + +static long futex_wait_restart(struct restart_block *restart); + +/** + * fixup_owner() - Post lock pi_state and corner case management + * @uaddr: user address of the futex + * @q: futex_q (contains pi_state and access to the rt_mutex) + * @locked: if the attempt to take the rt_mutex succeeded (1) or not (0) + * + * After attempting to lock an rt_mutex, this function is called to cleanup + * the pi_state owner as well as handle race conditions that may allow us to + * acquire the lock. Must be called with the hb lock held. + * + * Return: + * 1 - success, lock taken; + * 0 - success, lock not taken; + * <0 - on error (-EFAULT) + */ +static int fixup_owner(u32 __user *uaddr, struct futex_q *q, int locked) +{ + struct task_struct *owner; + int ret = 0; + + if (locked) { + /* + * Got the lock. We might not be the anticipated owner if we + * did a lock-steal - fix up the PI-state in that case: + */ + if (q->pi_state->owner != current) + ret = fixup_pi_state_owner(uaddr, q, current); + goto out; + } + + /* + * Catch the rare case, where the lock was released when we were on the + * way back before we locked the hash bucket. + */ + if (q->pi_state->owner == current) { + /* + * Try to get the rt_mutex now. This might fail as some other + * task acquired the rt_mutex after we removed ourself from the + * rt_mutex waiters list. + */ + if (rt_mutex_trylock(&q->pi_state->pi_mutex)) { + locked = 1; + goto out; + } + + /* + * pi_state is incorrect, some other task did a lock steal and + * we returned due to timeout or signal without taking the + * rt_mutex. Too late. + */ + raw_spin_lock(&q->pi_state->pi_mutex.wait_lock); + owner = rt_mutex_owner(&q->pi_state->pi_mutex); + if (!owner) + owner = rt_mutex_next_owner(&q->pi_state->pi_mutex); + raw_spin_unlock(&q->pi_state->pi_mutex.wait_lock); + ret = fixup_pi_state_owner(uaddr, q, owner); + goto out; + } + + /* + * Paranoia check. If we did not take the lock, then we should not be + * the owner of the rt_mutex. + */ + if (rt_mutex_owner(&q->pi_state->pi_mutex) == current) + printk(KERN_ERR "fixup_owner: ret = %d pi-mutex: %p " + "pi-state %p\n", ret, + q->pi_state->pi_mutex.owner, + q->pi_state->owner); + +out: + return ret ? ret : locked; +} + +/** + * futex_wait_queue_me() - queue_me() and wait for wakeup, timeout, or signal + * @hb: the futex hash bucket, must be locked by the caller + * @q: the futex_q to queue up on + * @timeout: the prepared hrtimer_sleeper, or null for no timeout + */ +static void futex_wait_queue_me(struct futex_hash_bucket *hb, struct futex_q *q, + struct hrtimer_sleeper *timeout) +{ + /* + * The task state is guaranteed to be set before another task can + * wake it. set_current_state() is implemented using set_mb() and + * queue_me() calls spin_unlock() upon completion, both serializing + * access to the hash list and forcing another memory barrier. + */ + set_current_state(TASK_INTERRUPTIBLE); + queue_me(q, hb); + + /* Arm the timer */ + if (timeout) { + hrtimer_start_expires(&timeout->timer, HRTIMER_MODE_ABS); + if (!hrtimer_active(&timeout->timer)) + timeout->task = NULL; + } + + /* + * If we have been removed from the hash list, then another task + * has tried to wake us, and we can skip the call to schedule(). + */ + if (likely(!plist_node_empty(&q->list))) { + /* + * If the timer has already expired, current will already be + * flagged for rescheduling. Only call schedule if there + * is no timeout, or if it has yet to expire. + */ + if (!timeout || timeout->task) + freezable_schedule(); + } + __set_current_state(TASK_RUNNING); +} - bh = queue_lock(&q, -1, NULL); +/** + * futex_wait_setup() - Prepare to wait on a futex + * @uaddr: the futex userspace address + * @val: the expected value + * @flags: futex flags (FLAGS_SHARED, etc.) + * @q: the associated futex_q + * @hb: storage for hash_bucket pointer to be returned to caller + * + * Setup the futex_q and locate the hash_bucket. Get the futex value and + * compare it with the expected value. Handle atomic faults internally. + * Return with the hb lock held and a q.key reference on success, and unlocked + * with no q.key reference on failure. + * + * Return: + * 0 - uaddr contains val and hb has been locked; + * <1 - -EFAULT or -EWOULDBLOCK (uaddr does not contain val) and hb is unlocked + */ +static int futex_wait_setup(u32 __user *uaddr, u32 val, unsigned int flags, + struct futex_q *q, struct futex_hash_bucket **hb) +{ + u32 uval; + int ret; /* - * Access the page AFTER the futex is queued. + * Access the page AFTER the hash-bucket is locked. * Order is important: * * Userspace waiter: val = var; if (cond(val)) futex_wait(&var, val); @@ -643,271 +2137,944 @@ static int futex_wait(unsigned long uaddr, int val, unsigned long time) * * The basic logical guarantee of a futex is that it blocks ONLY * if cond(var) is known to be true at the time of blocking, for - * any cond. If we queued after testing *uaddr, that would open - * a race condition where we could block indefinitely with + * any cond. If we locked the hash-bucket after testing *uaddr, that + * would open a race condition where we could block indefinitely with * cond(var) false, which would violate the guarantee. * - * A consequence is that futex_wait() can return zero and absorb - * a wakeup when *uaddr != val on entry to the syscall. This is - * rare, but normal. - * - * We hold the mmap semaphore, so the mapping cannot have changed - * since we looked it up in get_futex_key. + * On the other hand, we insert q and release the hash-bucket only + * after testing *uaddr. This guarantees that futex_wait() will NOT + * absorb a wakeup if *uaddr does not match the desired values + * while the syscall executes. */ +retry: + ret = get_futex_key(uaddr, flags & FLAGS_SHARED, &q->key, VERIFY_READ); + if (unlikely(ret != 0)) + return ret; - ret = get_futex_value_locked(&curval, (int __user *)uaddr); +retry_private: + *hb = queue_lock(q); - if (unlikely(ret)) { - queue_unlock(&q, bh); + ret = get_futex_value_locked(&uval, uaddr); - /* If we would have faulted, release mmap_sem, fault it in and - * start all over again. - */ - up_read(¤t->mm->mmap_sem); + if (ret) { + queue_unlock(*hb); + + ret = get_user(uval, uaddr); + if (ret) + goto out; - ret = get_user(curval, (int __user *)uaddr); + if (!(flags & FLAGS_SHARED)) + goto retry_private; - if (!ret) - goto retry; - return ret; + put_futex_key(&q->key); + goto retry; } - if (curval != val) { + + if (uval != val) { + queue_unlock(*hb); ret = -EWOULDBLOCK; - queue_unlock(&q, bh); - goto out_release_sem; } - /* Only actually queue if *uaddr contained val. */ - __queue_me(&q, bh); +out: + if (ret) + put_futex_key(&q->key); + return ret; +} + +static int futex_wait(u32 __user *uaddr, unsigned int flags, u32 val, + ktime_t *abs_time, u32 bitset) +{ + struct hrtimer_sleeper timeout, *to = NULL; + struct restart_block *restart; + struct futex_hash_bucket *hb; + struct futex_q q = futex_q_init; + int ret; + + if (!bitset) + return -EINVAL; + q.bitset = bitset; + + if (abs_time) { + to = &timeout; + + hrtimer_init_on_stack(&to->timer, (flags & FLAGS_CLOCKRT) ? + CLOCK_REALTIME : CLOCK_MONOTONIC, + HRTIMER_MODE_ABS); + hrtimer_init_sleeper(to, current); + hrtimer_set_expires_range_ns(&to->timer, *abs_time, + current->timer_slack_ns); + } + +retry: + /* + * Prepare to wait on uaddr. On success, holds hb lock and increments + * q.key refs. + */ + ret = futex_wait_setup(uaddr, val, flags, &q, &hb); + if (ret) + goto out; + + /* queue_me and wait for wakeup, timeout, or a signal. */ + futex_wait_queue_me(hb, &q, to); + + /* If we were woken (and unqueued), we succeeded, whatever. */ + ret = 0; + /* unqueue_me() drops q.key ref */ + if (!unqueue_me(&q)) + goto out; + ret = -ETIMEDOUT; + if (to && !to->task) + goto out; + + /* + * We expect signal_pending(current), but we might be the + * victim of a spurious wakeup as well. + */ + if (!signal_pending(current)) + goto retry; + + ret = -ERESTARTSYS; + if (!abs_time) + goto out; + + restart = ¤t_thread_info()->restart_block; + restart->fn = futex_wait_restart; + restart->futex.uaddr = uaddr; + restart->futex.val = val; + restart->futex.time = abs_time->tv64; + restart->futex.bitset = bitset; + restart->futex.flags = flags | FLAGS_HAS_TIMEOUT; + + ret = -ERESTART_RESTARTBLOCK; + +out: + if (to) { + hrtimer_cancel(&to->timer); + destroy_hrtimer_on_stack(&to->timer); + } + return ret; +} + + +static long futex_wait_restart(struct restart_block *restart) +{ + u32 __user *uaddr = restart->futex.uaddr; + ktime_t t, *tp = NULL; + + if (restart->futex.flags & FLAGS_HAS_TIMEOUT) { + t.tv64 = restart->futex.time; + tp = &t; + } + restart->fn = do_no_restart_syscall; + + return (long)futex_wait(uaddr, restart->futex.flags, + restart->futex.val, tp, restart->futex.bitset); +} + + +/* + * Userspace tried a 0 -> TID atomic transition of the futex value + * and failed. The kernel side here does the whole locking operation: + * if there are waiters then it will block, it does PI, etc. (Due to + * races the kernel might see a 0 value of the futex too.) + */ +static int futex_lock_pi(u32 __user *uaddr, unsigned int flags, int detect, + ktime_t *time, int trylock) +{ + struct hrtimer_sleeper timeout, *to = NULL; + struct futex_hash_bucket *hb; + struct futex_q q = futex_q_init; + int res, ret; + + if (refill_pi_state_cache()) + return -ENOMEM; + + if (time) { + to = &timeout; + hrtimer_init_on_stack(&to->timer, CLOCK_REALTIME, + HRTIMER_MODE_ABS); + hrtimer_init_sleeper(to, current); + hrtimer_set_expires(&to->timer, *time); + } + +retry: + ret = get_futex_key(uaddr, flags & FLAGS_SHARED, &q.key, VERIFY_WRITE); + if (unlikely(ret != 0)) + goto out; + +retry_private: + hb = queue_lock(&q); + + ret = futex_lock_pi_atomic(uaddr, hb, &q.key, &q.pi_state, current, 0); + if (unlikely(ret)) { + switch (ret) { + case 1: + /* We got the lock. */ + ret = 0; + goto out_unlock_put_key; + case -EFAULT: + goto uaddr_faulted; + case -EAGAIN: + /* + * Task is exiting and we just wait for the + * exit to complete. + */ + queue_unlock(hb); + put_futex_key(&q.key); + cond_resched(); + goto retry; + default: + goto out_unlock_put_key; + } + } /* - * Now the futex is queued and we have checked the data, we - * don't want to hold mmap_sem while we sleep. - */ - up_read(¤t->mm->mmap_sem); + * Only actually queue now that the atomic ops are done: + */ + queue_me(&q, hb); + WARN_ON(!q.pi_state); /* - * There might have been scheduling since the queue_me(), as we - * cannot hold a spinlock across the get_user() in case it - * faults, and we cannot just set TASK_INTERRUPTIBLE state when - * queueing ourselves into the futex hash. This code thus has to - * rely on the futex_wake() code removing us from hash when it - * wakes us up. + * Block on the PI mutex: */ + if (!trylock) + ret = rt_mutex_timed_lock(&q.pi_state->pi_mutex, to, 1); + else { + ret = rt_mutex_trylock(&q.pi_state->pi_mutex); + /* Fixup the trylock return value: */ + ret = ret ? 0 : -EWOULDBLOCK; + } - /* add_wait_queue is the barrier after __set_current_state. */ - __set_current_state(TASK_INTERRUPTIBLE); - add_wait_queue(&q.waiters, &wait); + spin_lock(q.lock_ptr); /* - * !list_empty() is safe here without any lock. - * q.lock_ptr != 0 is not safe, because of ordering against wakeup. + * Fixup the pi_state owner and possibly acquire the lock if we + * haven't already. */ - if (likely(!list_empty(&q.list))) - time = schedule_timeout(time); - __set_current_state(TASK_RUNNING); + res = fixup_owner(uaddr, &q, !ret); + /* + * If fixup_owner() returned an error, proprogate that. If it acquired + * the lock, clear our -ETIMEDOUT or -EINTR. + */ + if (res) + ret = (res < 0) ? res : 0; /* - * NOTE: we don't remove ourselves from the waitqueue because - * we are the only user of it. + * If fixup_owner() faulted and was unable to handle the fault, unlock + * it and return the fault to userspace. */ + if (ret && (rt_mutex_owner(&q.pi_state->pi_mutex) == current)) + rt_mutex_unlock(&q.pi_state->pi_mutex); - /* If we were woken (and unqueued), we succeeded, whatever. */ - if (!unqueue_me(&q)) - return 0; - if (time == 0) - return -ETIMEDOUT; - /* We expect signal_pending(current), but another thread may - * have handled it for us already. */ - return -EINTR; - - out_release_sem: - up_read(¤t->mm->mmap_sem); - return ret; + /* Unqueue and drop the lock */ + unqueue_me_pi(&q); + + goto out_put_key; + +out_unlock_put_key: + queue_unlock(hb); + +out_put_key: + put_futex_key(&q.key); +out: + if (to) + destroy_hrtimer_on_stack(&to->timer); + return ret != -EINTR ? ret : -ERESTARTNOINTR; + +uaddr_faulted: + queue_unlock(hb); + + ret = fault_in_user_writeable(uaddr); + if (ret) + goto out_put_key; + + if (!(flags & FLAGS_SHARED)) + goto retry_private; + + put_futex_key(&q.key); + goto retry; } -static int futex_close(struct inode *inode, struct file *filp) +/* + * Userspace attempted a TID -> 0 atomic transition, and failed. + * This is the in-kernel slowpath: we look up the PI state (if any), + * and do the rt-mutex unlock. + */ +static int futex_unlock_pi(u32 __user *uaddr, unsigned int flags) { - struct futex_q *q = filp->private_data; + struct futex_hash_bucket *hb; + struct futex_q *this, *next; + union futex_key key = FUTEX_KEY_INIT; + u32 uval, vpid = task_pid_vnr(current); + int ret; - unqueue_me(q); - kfree(q); - return 0; +retry: + if (get_user(uval, uaddr)) + return -EFAULT; + /* + * We release only a lock we actually own: + */ + if ((uval & FUTEX_TID_MASK) != vpid) + return -EPERM; + + ret = get_futex_key(uaddr, flags & FLAGS_SHARED, &key, VERIFY_WRITE); + if (unlikely(ret != 0)) + goto out; + + hb = hash_futex(&key); + spin_lock(&hb->lock); + + /* + * To avoid races, try to do the TID -> 0 atomic transition + * again. If it succeeds then we can return without waking + * anyone else up. We only try this if neither the waiters nor + * the owner died bit are set. + */ + if (!(uval & ~FUTEX_TID_MASK) && + cmpxchg_futex_value_locked(&uval, uaddr, vpid, 0)) + goto pi_faulted; + /* + * Rare case: we managed to release the lock atomically, + * no need to wake anyone else up: + */ + if (unlikely(uval == vpid)) + goto out_unlock; + + /* + * Ok, other tasks may need to be woken up - check waiters + * and do the wakeup if necessary: + */ + plist_for_each_entry_safe(this, next, &hb->chain, list) { + if (!match_futex (&this->key, &key)) + continue; + ret = wake_futex_pi(uaddr, uval, this); + /* + * The atomic access to the futex value + * generated a pagefault, so retry the + * user-access and the wakeup: + */ + if (ret == -EFAULT) + goto pi_faulted; + goto out_unlock; + } + /* + * No waiters - kernel unlocks the futex: + */ + ret = unlock_futex_pi(uaddr, uval); + if (ret == -EFAULT) + goto pi_faulted; + +out_unlock: + spin_unlock(&hb->lock); + put_futex_key(&key); + +out: + return ret; + +pi_faulted: + spin_unlock(&hb->lock); + put_futex_key(&key); + + ret = fault_in_user_writeable(uaddr); + if (!ret) + goto retry; + + return ret; } -/* This is one-shot: once it's gone off you need a new fd */ -static unsigned int futex_poll(struct file *filp, - struct poll_table_struct *wait) +/** + * handle_early_requeue_pi_wakeup() - Detect early wakeup on the initial futex + * @hb: the hash_bucket futex_q was original enqueued on + * @q: the futex_q woken while waiting to be requeued + * @key2: the futex_key of the requeue target futex + * @timeout: the timeout associated with the wait (NULL if none) + * + * Detect if the task was woken on the initial futex as opposed to the requeue + * target futex. If so, determine if it was a timeout or a signal that caused + * the wakeup and return the appropriate error code to the caller. Must be + * called with the hb lock held. + * + * Return: + * 0 = no early wakeup detected; + * <0 = -ETIMEDOUT or -ERESTARTNOINTR + */ +static inline +int handle_early_requeue_pi_wakeup(struct futex_hash_bucket *hb, + struct futex_q *q, union futex_key *key2, + struct hrtimer_sleeper *timeout) { - struct futex_q *q = filp->private_data; int ret = 0; - poll_wait(filp, &q->waiters, wait); - /* - * list_empty() is safe here without any lock. - * q->lock_ptr != 0 is not safe, because of ordering against wakeup. + * With the hb lock held, we avoid races while we process the wakeup. + * We only need to hold hb (and not hb2) to ensure atomicity as the + * wakeup code can't change q.key from uaddr to uaddr2 if we hold hb. + * It can't be requeued from uaddr2 to something else since we don't + * support a PI aware source futex for requeue. */ - if (list_empty(&q->list)) - ret = POLLIN | POLLRDNORM; + if (!match_futex(&q->key, key2)) { + WARN_ON(q->lock_ptr && (&hb->lock != q->lock_ptr)); + /* + * We were woken prior to requeue by a timeout or a signal. + * Unqueue the futex_q and determine which it was. + */ + plist_del(&q->list, &hb->chain); + hb_waiters_dec(hb); + /* Handle spurious wakeups gracefully */ + ret = -EWOULDBLOCK; + if (timeout && !timeout->task) + ret = -ETIMEDOUT; + else if (signal_pending(current)) + ret = -ERESTARTNOINTR; + } return ret; } -static struct file_operations futex_fops = { - .release = futex_close, - .poll = futex_poll, -}; - -/* - * Signal allows caller to avoid the race which would occur if they - * set the sigio stuff up afterwards. +/** + * futex_wait_requeue_pi() - Wait on uaddr and take uaddr2 + * @uaddr: the futex we initially wait on (non-pi) + * @flags: futex flags (FLAGS_SHARED, FLAGS_CLOCKRT, etc.), they must be + * the same type, no requeueing from private to shared, etc. + * @val: the expected value of uaddr + * @abs_time: absolute timeout + * @bitset: 32 bit wakeup bitset set by userspace, defaults to all + * @uaddr2: the pi futex we will take prior to returning to user-space + * + * The caller will wait on uaddr and will be requeued by futex_requeue() to + * uaddr2 which must be PI aware and unique from uaddr. Normal wakeup will wake + * on uaddr2 and complete the acquisition of the rt_mutex prior to returning to + * userspace. This ensures the rt_mutex maintains an owner when it has waiters; + * without one, the pi logic would not know which task to boost/deboost, if + * there was a need to. + * + * We call schedule in futex_wait_queue_me() when we enqueue and return there + * via the following-- + * 1) wakeup on uaddr2 after an atomic lock acquisition by futex_requeue() + * 2) wakeup on uaddr2 after a requeue + * 3) signal + * 4) timeout + * + * If 3, cleanup and return -ERESTARTNOINTR. + * + * If 2, we may then block on trying to take the rt_mutex and return via: + * 5) successful lock + * 6) signal + * 7) timeout + * 8) other lock acquisition failure + * + * If 6, return -EWOULDBLOCK (restarting the syscall would do the same). + * + * If 4 or 7, we cleanup and return with -ETIMEDOUT. + * + * Return: + * 0 - On success; + * <0 - On error */ -static int futex_fd(unsigned long uaddr, int signal) +static int futex_wait_requeue_pi(u32 __user *uaddr, unsigned int flags, + u32 val, ktime_t *abs_time, u32 bitset, + u32 __user *uaddr2) { - struct futex_q *q; - struct file *filp; - int ret, err; + struct hrtimer_sleeper timeout, *to = NULL; + struct rt_mutex_waiter rt_waiter; + struct rt_mutex *pi_mutex = NULL; + struct futex_hash_bucket *hb; + union futex_key key2 = FUTEX_KEY_INIT; + struct futex_q q = futex_q_init; + int res, ret; + + if (uaddr == uaddr2) + return -EINVAL; - ret = -EINVAL; - if (!valid_signal(signal)) - goto out; + if (!bitset) + return -EINVAL; - ret = get_unused_fd(); - if (ret < 0) - goto out; - filp = get_empty_filp(); - if (!filp) { - put_unused_fd(ret); - ret = -ENFILE; + if (abs_time) { + to = &timeout; + hrtimer_init_on_stack(&to->timer, (flags & FLAGS_CLOCKRT) ? + CLOCK_REALTIME : CLOCK_MONOTONIC, + HRTIMER_MODE_ABS); + hrtimer_init_sleeper(to, current); + hrtimer_set_expires_range_ns(&to->timer, *abs_time, + current->timer_slack_ns); + } + + /* + * The waiter is allocated on our stack, manipulated by the requeue + * code while we sleep on uaddr. + */ + debug_rt_mutex_init_waiter(&rt_waiter); + RB_CLEAR_NODE(&rt_waiter.pi_tree_entry); + RB_CLEAR_NODE(&rt_waiter.tree_entry); + rt_waiter.task = NULL; + + ret = get_futex_key(uaddr2, flags & FLAGS_SHARED, &key2, VERIFY_WRITE); + if (unlikely(ret != 0)) goto out; + + q.bitset = bitset; + q.rt_waiter = &rt_waiter; + q.requeue_pi_key = &key2; + + /* + * Prepare to wait on uaddr. On success, increments q.key (key1) ref + * count. + */ + ret = futex_wait_setup(uaddr, val, flags, &q, &hb); + if (ret) + goto out_key2; + + /* + * The check above which compares uaddrs is not sufficient for + * shared futexes. We need to compare the keys: + */ + if (match_futex(&q.key, &key2)) { + ret = -EINVAL; + goto out_put_keys; } - filp->f_op = &futex_fops; - filp->f_vfsmnt = mntget(futex_mnt); - filp->f_dentry = dget(futex_mnt->mnt_root); - filp->f_mapping = filp->f_dentry->d_inode->i_mapping; - if (signal) { - err = f_setown(filp, current->pid, 1); - if (err < 0) { - goto error; + /* Queue the futex_q, drop the hb lock, wait for wakeup. */ + futex_wait_queue_me(hb, &q, to); + + spin_lock(&hb->lock); + ret = handle_early_requeue_pi_wakeup(hb, &q, &key2, to); + spin_unlock(&hb->lock); + if (ret) + goto out_put_keys; + + /* + * In order for us to be here, we know our q.key == key2, and since + * we took the hb->lock above, we also know that futex_requeue() has + * completed and we no longer have to concern ourselves with a wakeup + * race with the atomic proxy lock acquisition by the requeue code. The + * futex_requeue dropped our key1 reference and incremented our key2 + * reference count. + */ + + /* Check if the requeue code acquired the second futex for us. */ + if (!q.rt_waiter) { + /* + * Got the lock. We might not be the anticipated owner if we + * did a lock-steal - fix up the PI-state in that case. + */ + if (q.pi_state && (q.pi_state->owner != current)) { + spin_lock(q.lock_ptr); + ret = fixup_pi_state_owner(uaddr2, &q, current); + spin_unlock(q.lock_ptr); } - filp->f_owner.signum = signal; + } else { + /* + * We have been woken up by futex_unlock_pi(), a timeout, or a + * signal. futex_unlock_pi() will not destroy the lock_ptr nor + * the pi_state. + */ + WARN_ON(!q.pi_state); + pi_mutex = &q.pi_state->pi_mutex; + ret = rt_mutex_finish_proxy_lock(pi_mutex, to, &rt_waiter, 1); + debug_rt_mutex_free_waiter(&rt_waiter); + + spin_lock(q.lock_ptr); + /* + * Fixup the pi_state owner and possibly acquire the lock if we + * haven't already. + */ + res = fixup_owner(uaddr2, &q, !ret); + /* + * If fixup_owner() returned an error, proprogate that. If it + * acquired the lock, clear -ETIMEDOUT or -EINTR. + */ + if (res) + ret = (res < 0) ? res : 0; + + /* Unqueue and drop the lock. */ + unqueue_me_pi(&q); } - q = kmalloc(sizeof(*q), GFP_KERNEL); - if (!q) { - err = -ENOMEM; - goto error; + /* + * If fixup_pi_state_owner() faulted and was unable to handle the + * fault, unlock the rt_mutex and return the fault to userspace. + */ + if (ret == -EFAULT) { + if (pi_mutex && rt_mutex_owner(pi_mutex) == current) + rt_mutex_unlock(pi_mutex); + } else if (ret == -EINTR) { + /* + * We've already been requeued, but cannot restart by calling + * futex_lock_pi() directly. We could restart this syscall, but + * it would detect that the user space "val" changed and return + * -EWOULDBLOCK. Save the overhead of the restart and return + * -EWOULDBLOCK directly. + */ + ret = -EWOULDBLOCK; } - down_read(¤t->mm->mmap_sem); - err = get_futex_key(uaddr, &q->key); +out_put_keys: + put_futex_key(&q.key); +out_key2: + put_futex_key(&key2); - if (unlikely(err != 0)) { - up_read(¤t->mm->mmap_sem); - kfree(q); - goto error; +out: + if (to) { + hrtimer_cancel(&to->timer); + destroy_hrtimer_on_stack(&to->timer); } + return ret; +} + +/* + * Support for robust futexes: the kernel cleans up held futexes at + * thread exit time. + * + * Implementation: user-space maintains a per-thread list of locks it + * is holding. Upon do_exit(), the kernel carefully walks this list, + * and marks all locks that are owned by this thread with the + * FUTEX_OWNER_DIED bit, and wakes up a waiter (if any). The list is + * always manipulated with the lock held, so the list is private and + * per-thread. Userspace also maintains a per-thread 'list_op_pending' + * field, to allow the kernel to clean up if the thread dies after + * acquiring the lock, but just before it could have added itself to + * the list. There can only be one such pending lock. + */ +/** + * sys_set_robust_list() - Set the robust-futex list head of a task + * @head: pointer to the list-head + * @len: length of the list-head, as userspace expects + */ +SYSCALL_DEFINE2(set_robust_list, struct robust_list_head __user *, head, + size_t, len) +{ + if (!futex_cmpxchg_enabled) + return -ENOSYS; /* - * queue_me() must be called before releasing mmap_sem, because - * key->shared.inode needs to be referenced while holding it. + * The kernel knows only one size for now: */ - filp->private_data = q; + if (unlikely(len != sizeof(*head))) + return -EINVAL; - queue_me(q, ret, filp); - up_read(¤t->mm->mmap_sem); + current->robust_list = head; + + return 0; +} + +/** + * sys_get_robust_list() - Get the robust-futex list head of a task + * @pid: pid of the process [zero for current task] + * @head_ptr: pointer to a list-head pointer, the kernel fills it in + * @len_ptr: pointer to a length field, the kernel fills in the header size + */ +SYSCALL_DEFINE3(get_robust_list, int, pid, + struct robust_list_head __user * __user *, head_ptr, + size_t __user *, len_ptr) +{ + struct robust_list_head __user *head; + unsigned long ret; + struct task_struct *p; + + if (!futex_cmpxchg_enabled) + return -ENOSYS; + + rcu_read_lock(); + + ret = -ESRCH; + if (!pid) + p = current; + else { + p = find_task_by_vpid(pid); + if (!p) + goto err_unlock; + } + + ret = -EPERM; + if (!ptrace_may_access(p, PTRACE_MODE_READ)) + goto err_unlock; + + head = p->robust_list; + rcu_read_unlock(); + + if (put_user(sizeof(*head), len_ptr)) + return -EFAULT; + return put_user(head, head_ptr); + +err_unlock: + rcu_read_unlock(); - /* Now we map fd to filp, so userspace can access it */ - fd_install(ret, filp); -out: return ret; -error: - put_unused_fd(ret); - put_filp(filp); - ret = err; - goto out; } -long do_futex(unsigned long uaddr, int op, int val, unsigned long timeout, - unsigned long uaddr2, int val2, int val3) +/* + * Process a futex-list entry, check whether it's owned by the + * dying task, and do notification if so: + */ +int handle_futex_death(u32 __user *uaddr, struct task_struct *curr, int pi) { - int ret; + u32 uval, uninitialized_var(nval), mval; + +retry: + if (get_user(uval, uaddr)) + return -1; + + if ((uval & FUTEX_TID_MASK) == task_pid_vnr(curr)) { + /* + * Ok, this dying thread is truly holding a futex + * of interest. Set the OWNER_DIED bit atomically + * via cmpxchg, and if the value had FUTEX_WAITERS + * set, wake up a waiter (if any). (We have to do a + * futex_wake() even if OWNER_DIED is already set - + * to handle the rare but possible case of recursive + * thread-death.) The rest of the cleanup is done in + * userspace. + */ + mval = (uval & FUTEX_WAITERS) | FUTEX_OWNER_DIED; + /* + * We are not holding a lock here, but we want to have + * the pagefault_disable/enable() protection because + * we want to handle the fault gracefully. If the + * access fails we try to fault in the futex with R/W + * verification via get_user_pages. get_user() above + * does not guarantee R/W access. If that fails we + * give up and leave the futex locked. + */ + if (cmpxchg_futex_value_locked(&nval, uaddr, uval, mval)) { + if (fault_in_user_writeable(uaddr)) + return -1; + goto retry; + } + if (nval != uval) + goto retry; + + /* + * Wake robust non-PI futexes here. The wakeup of + * PI futexes happens in exit_pi_state(): + */ + if (!pi && (uval & FUTEX_WAITERS)) + futex_wake(uaddr, 1, 1, FUTEX_BITSET_MATCH_ANY); + } + return 0; +} + +/* + * Fetch a robust-list pointer. Bit 0 signals PI futexes: + */ +static inline int fetch_robust_entry(struct robust_list __user **entry, + struct robust_list __user * __user *head, + unsigned int *pi) +{ + unsigned long uentry; - switch (op) { + if (get_user(uentry, (unsigned long __user *)head)) + return -EFAULT; + + *entry = (void __user *)(uentry & ~1UL); + *pi = uentry & 1; + + return 0; +} + +/* + * Walk curr->robust_list (very carefully, it's a userspace list!) + * and mark any locks found there dead, and notify any waiters. + * + * We silently return on any sign of list-walking problem. + */ +void exit_robust_list(struct task_struct *curr) +{ + struct robust_list_head __user *head = curr->robust_list; + struct robust_list __user *entry, *next_entry, *pending; + unsigned int limit = ROBUST_LIST_LIMIT, pi, pip; + unsigned int uninitialized_var(next_pi); + unsigned long futex_offset; + int rc; + + if (!futex_cmpxchg_enabled) + return; + + /* + * Fetch the list head (which was registered earlier, via + * sys_set_robust_list()): + */ + if (fetch_robust_entry(&entry, &head->list.next, &pi)) + return; + /* + * Fetch the relative futex offset: + */ + if (get_user(futex_offset, &head->futex_offset)) + return; + /* + * Fetch any possibly pending lock-add first, and handle it + * if it exists: + */ + if (fetch_robust_entry(&pending, &head->list_op_pending, &pip)) + return; + + next_entry = NULL; /* avoid warning with gcc */ + while (entry != &head->list) { + /* + * Fetch the next entry in the list before calling + * handle_futex_death: + */ + rc = fetch_robust_entry(&next_entry, &entry->next, &next_pi); + /* + * A pending lock might already be on the list, so + * don't process it twice: + */ + if (entry != pending) + if (handle_futex_death((void __user *)entry + futex_offset, + curr, pi)) + return; + if (rc) + return; + entry = next_entry; + pi = next_pi; + /* + * Avoid excessively long or circular lists: + */ + if (!--limit) + break; + + cond_resched(); + } + + if (pending) + handle_futex_death((void __user *)pending + futex_offset, + curr, pip); +} + +long do_futex(u32 __user *uaddr, int op, u32 val, ktime_t *timeout, + u32 __user *uaddr2, u32 val2, u32 val3) +{ + int cmd = op & FUTEX_CMD_MASK; + unsigned int flags = 0; + + if (!(op & FUTEX_PRIVATE_FLAG)) + flags |= FLAGS_SHARED; + + if (op & FUTEX_CLOCK_REALTIME) { + flags |= FLAGS_CLOCKRT; + if (cmd != FUTEX_WAIT_BITSET && cmd != FUTEX_WAIT_REQUEUE_PI) + return -ENOSYS; + } + + switch (cmd) { + case FUTEX_LOCK_PI: + case FUTEX_UNLOCK_PI: + case FUTEX_TRYLOCK_PI: + case FUTEX_WAIT_REQUEUE_PI: + case FUTEX_CMP_REQUEUE_PI: + if (!futex_cmpxchg_enabled) + return -ENOSYS; + } + + switch (cmd) { case FUTEX_WAIT: - ret = futex_wait(uaddr, val, timeout); - break; + val3 = FUTEX_BITSET_MATCH_ANY; + case FUTEX_WAIT_BITSET: + return futex_wait(uaddr, flags, val, timeout, val3); case FUTEX_WAKE: - ret = futex_wake(uaddr, val); - break; - case FUTEX_FD: - /* non-zero val means F_SETOWN(getpid()) & F_SETSIG(val) */ - ret = futex_fd(uaddr, val); - break; + val3 = FUTEX_BITSET_MATCH_ANY; + case FUTEX_WAKE_BITSET: + return futex_wake(uaddr, flags, val, val3); case FUTEX_REQUEUE: - ret = futex_requeue(uaddr, uaddr2, val, val2, NULL); - break; + return futex_requeue(uaddr, flags, uaddr2, val, val2, NULL, 0); case FUTEX_CMP_REQUEUE: - ret = futex_requeue(uaddr, uaddr2, val, val2, &val3); - break; + return futex_requeue(uaddr, flags, uaddr2, val, val2, &val3, 0); case FUTEX_WAKE_OP: - ret = futex_wake_op(uaddr, uaddr2, val, val2, val3); - break; - default: - ret = -ENOSYS; + return futex_wake_op(uaddr, flags, uaddr2, val, val2, val3); + case FUTEX_LOCK_PI: + return futex_lock_pi(uaddr, flags, val, timeout, 0); + case FUTEX_UNLOCK_PI: + return futex_unlock_pi(uaddr, flags); + case FUTEX_TRYLOCK_PI: + return futex_lock_pi(uaddr, flags, 0, timeout, 1); + case FUTEX_WAIT_REQUEUE_PI: + val3 = FUTEX_BITSET_MATCH_ANY; + return futex_wait_requeue_pi(uaddr, flags, val, timeout, val3, + uaddr2); + case FUTEX_CMP_REQUEUE_PI: + return futex_requeue(uaddr, flags, uaddr2, val, val2, &val3, 1); } - return ret; + return -ENOSYS; } -asmlinkage long sys_futex(u32 __user *uaddr, int op, int val, - struct timespec __user *utime, u32 __user *uaddr2, - int val3) +SYSCALL_DEFINE6(futex, u32 __user *, uaddr, int, op, u32, val, + struct timespec __user *, utime, u32 __user *, uaddr2, + u32, val3) { - struct timespec t; - unsigned long timeout = MAX_SCHEDULE_TIMEOUT; - int val2 = 0; - - if ((op == FUTEX_WAIT) && utime) { - if (copy_from_user(&t, utime, sizeof(t)) != 0) + struct timespec ts; + ktime_t t, *tp = NULL; + u32 val2 = 0; + int cmd = op & FUTEX_CMD_MASK; + + if (utime && (cmd == FUTEX_WAIT || cmd == FUTEX_LOCK_PI || + cmd == FUTEX_WAIT_BITSET || + cmd == FUTEX_WAIT_REQUEUE_PI)) { + if (copy_from_user(&ts, utime, sizeof(ts)) != 0) return -EFAULT; - timeout = timespec_to_jiffies(&t) + 1; + if (!timespec_valid(&ts)) + return -EINVAL; + + t = timespec_to_ktime(ts); + if (cmd == FUTEX_WAIT) + t = ktime_add_safe(ktime_get(), t); + tp = &t; } /* - * requeue parameter in 'utime' if op == FUTEX_REQUEUE. + * requeue parameter in 'utime' if cmd == FUTEX_*_REQUEUE_*. + * number of waiters to wake in 'utime' if cmd == FUTEX_WAKE_OP. */ - if (op >= FUTEX_REQUEUE) - val2 = (int) (unsigned long) utime; + if (cmd == FUTEX_REQUEUE || cmd == FUTEX_CMP_REQUEUE || + cmd == FUTEX_CMP_REQUEUE_PI || cmd == FUTEX_WAKE_OP) + val2 = (u32) (unsigned long) utime; - return do_futex((unsigned long)uaddr, op, val, timeout, - (unsigned long)uaddr2, val2, val3); + return do_futex(uaddr, op, val, tp, uaddr2, val2, val3); } -static struct super_block * -futexfs_get_sb(struct file_system_type *fs_type, - int flags, const char *dev_name, void *data) +static void __init futex_detect_cmpxchg(void) { - return get_sb_pseudo(fs_type, "futex", NULL, 0xBAD1DEA); -} +#ifndef CONFIG_HAVE_FUTEX_CMPXCHG + u32 curval; -static struct file_system_type futex_fs_type = { - .name = "futexfs", - .get_sb = futexfs_get_sb, - .kill_sb = kill_anon_super, -}; + /* + * This will fail and we want it. Some arch implementations do + * runtime detection of the futex_atomic_cmpxchg_inatomic() + * functionality. We want to know that before we call in any + * of the complex code paths. Also we want to prevent + * registration of robust lists in that case. NULL is + * guaranteed to fault and we get -EFAULT on functional + * implementation, the non-functional ones will return + * -ENOSYS. + */ + if (cmpxchg_futex_value_locked(&curval, NULL, 0, 0) == -EFAULT) + futex_cmpxchg_enabled = 1; +#endif +} -static int __init init(void) +static int __init futex_init(void) { - unsigned int i; + unsigned int futex_shift; + unsigned long i; - register_filesystem(&futex_fs_type); - futex_mnt = kern_mount(&futex_fs_type); +#if CONFIG_BASE_SMALL + futex_hashsize = 16; +#else + futex_hashsize = roundup_pow_of_two(256 * num_possible_cpus()); +#endif - for (i = 0; i < ARRAY_SIZE(futex_queues); i++) { - INIT_LIST_HEAD(&futex_queues[i].chain); + futex_queues = alloc_large_system_hash("futex", sizeof(*futex_queues), + futex_hashsize, 0, + futex_hashsize < 256 ? HASH_SMALL : 0, + &futex_shift, NULL, + futex_hashsize, futex_hashsize); + futex_hashsize = 1UL << futex_shift; + + futex_detect_cmpxchg(); + + for (i = 0; i < futex_hashsize; i++) { + atomic_set(&futex_queues[i].waiters, 0); + plist_head_init(&futex_queues[i].chain); spin_lock_init(&futex_queues[i].lock); } + return 0; } -__initcall(init); +__initcall(futex_init); |