diff options
Diffstat (limited to 'kernel/rcutiny_plugin.h')
| -rw-r--r-- | kernel/rcutiny_plugin.h | 615 |
1 files changed, 0 insertions, 615 deletions
diff --git a/kernel/rcutiny_plugin.h b/kernel/rcutiny_plugin.h deleted file mode 100644 index 6ceca4f745f..00000000000 --- a/kernel/rcutiny_plugin.h +++ /dev/null @@ -1,615 +0,0 @@ -/* - * Read-Copy Update mechanism for mutual exclusion, the Bloatwatch edition - * Internal non-public definitions that provide either classic - * or preemptible semantics. - * - * This program is free software; you can redistribute it and/or modify - * it under the terms of the GNU General Public License as published by - * the Free Software Foundation; either version 2 of the License, or - * (at your option) any later version. - * - * This program is distributed in the hope that it will be useful, - * but WITHOUT ANY WARRANTY; without even the implied warranty of - * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the - * GNU General Public License for more details. - * - * You should have received a copy of the GNU General Public License - * along with this program; if not, write to the Free Software - * Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA. - * - * Copyright (c) 2010 Linaro - * - * Author: Paul E. McKenney <paulmck@linux.vnet.ibm.com> - */ - -#ifdef CONFIG_TINY_PREEMPT_RCU - -#include <linux/delay.h> - -/* Global control variables for preemptible RCU. */ -struct rcu_preempt_ctrlblk { - struct rcu_ctrlblk rcb; /* curtail: ->next ptr of last CB for GP. */ - struct rcu_head **nexttail; - /* Tasks blocked in a preemptible RCU */ - /* read-side critical section while an */ - /* preemptible-RCU grace period is in */ - /* progress must wait for a later grace */ - /* period. This pointer points to the */ - /* ->next pointer of the last task that */ - /* must wait for a later grace period, or */ - /* to &->rcb.rcucblist if there is no */ - /* such task. */ - struct list_head blkd_tasks; - /* Tasks blocked in RCU read-side critical */ - /* section. Tasks are placed at the head */ - /* of this list and age towards the tail. */ - struct list_head *gp_tasks; - /* Pointer to the first task blocking the */ - /* current grace period, or NULL if there */ - /* is not such task. */ - struct list_head *exp_tasks; - /* Pointer to first task blocking the */ - /* current expedited grace period, or NULL */ - /* if there is no such task. If there */ - /* is no current expedited grace period, */ - /* then there cannot be any such task. */ - u8 gpnum; /* Current grace period. */ - u8 gpcpu; /* Last grace period blocked by the CPU. */ - u8 completed; /* Last grace period completed. */ - /* If all three are equal, RCU is idle. */ -}; - -static struct rcu_preempt_ctrlblk rcu_preempt_ctrlblk = { - .rcb.donetail = &rcu_preempt_ctrlblk.rcb.rcucblist, - .rcb.curtail = &rcu_preempt_ctrlblk.rcb.rcucblist, - .nexttail = &rcu_preempt_ctrlblk.rcb.rcucblist, - .blkd_tasks = LIST_HEAD_INIT(rcu_preempt_ctrlblk.blkd_tasks), -}; - -static int rcu_preempted_readers_exp(void); -static void rcu_report_exp_done(void); - -/* - * Return true if the CPU has not yet responded to the current grace period. - */ -static int rcu_cpu_blocking_cur_gp(void) -{ - return rcu_preempt_ctrlblk.gpcpu != rcu_preempt_ctrlblk.gpnum; -} - -/* - * Check for a running RCU reader. Because there is only one CPU, - * there can be but one running RCU reader at a time. ;-) - */ -static int rcu_preempt_running_reader(void) -{ - return current->rcu_read_lock_nesting; -} - -/* - * Check for preempted RCU readers blocking any grace period. - * If the caller needs a reliable answer, it must disable hard irqs. - */ -static int rcu_preempt_blocked_readers_any(void) -{ - return !list_empty(&rcu_preempt_ctrlblk.blkd_tasks); -} - -/* - * Check for preempted RCU readers blocking the current grace period. - * If the caller needs a reliable answer, it must disable hard irqs. - */ -static int rcu_preempt_blocked_readers_cgp(void) -{ - return rcu_preempt_ctrlblk.gp_tasks != NULL; -} - -/* - * Return true if another preemptible-RCU grace period is needed. - */ -static int rcu_preempt_needs_another_gp(void) -{ - return *rcu_preempt_ctrlblk.rcb.curtail != NULL; -} - -/* - * Return true if a preemptible-RCU grace period is in progress. - * The caller must disable hardirqs. - */ -static int rcu_preempt_gp_in_progress(void) -{ - return rcu_preempt_ctrlblk.completed != rcu_preempt_ctrlblk.gpnum; -} - -/* - * Record a preemptible-RCU quiescent state for the specified CPU. Note - * that this just means that the task currently running on the CPU is - * in a quiescent state. There might be any number of tasks blocked - * while in an RCU read-side critical section. - * - * Unlike the other rcu_*_qs() functions, callers to this function - * must disable irqs in order to protect the assignment to - * ->rcu_read_unlock_special. - * - * Because this is a single-CPU implementation, the only way a grace - * period can end is if the CPU is in a quiescent state. The reason is - * that a blocked preemptible-RCU reader can exit its critical section - * only if the CPU is running it at the time. Therefore, when the - * last task blocking the current grace period exits its RCU read-side - * critical section, neither the CPU nor blocked tasks will be stopping - * the current grace period. (In contrast, SMP implementations - * might have CPUs running in RCU read-side critical sections that - * block later grace periods -- but this is not possible given only - * one CPU.) - */ -static void rcu_preempt_cpu_qs(void) -{ - /* Record both CPU and task as having responded to current GP. */ - rcu_preempt_ctrlblk.gpcpu = rcu_preempt_ctrlblk.gpnum; - current->rcu_read_unlock_special &= ~RCU_READ_UNLOCK_NEED_QS; - - /* - * If there is no GP, or if blocked readers are still blocking GP, - * then there is nothing more to do. - */ - if (!rcu_preempt_gp_in_progress() || rcu_preempt_blocked_readers_cgp()) - return; - - /* Advance callbacks. */ - rcu_preempt_ctrlblk.completed = rcu_preempt_ctrlblk.gpnum; - rcu_preempt_ctrlblk.rcb.donetail = rcu_preempt_ctrlblk.rcb.curtail; - rcu_preempt_ctrlblk.rcb.curtail = rcu_preempt_ctrlblk.nexttail; - - /* If there are no blocked readers, next GP is done instantly. */ - if (!rcu_preempt_blocked_readers_any()) - rcu_preempt_ctrlblk.rcb.donetail = rcu_preempt_ctrlblk.nexttail; - - /* If there are done callbacks, make RCU_SOFTIRQ process them. */ - if (*rcu_preempt_ctrlblk.rcb.donetail != NULL) - raise_softirq(RCU_SOFTIRQ); -} - -/* - * Start a new RCU grace period if warranted. Hard irqs must be disabled. - */ -static void rcu_preempt_start_gp(void) -{ - if (!rcu_preempt_gp_in_progress() && rcu_preempt_needs_another_gp()) { - - /* Official start of GP. */ - rcu_preempt_ctrlblk.gpnum++; - - /* Any blocked RCU readers block new GP. */ - if (rcu_preempt_blocked_readers_any()) - rcu_preempt_ctrlblk.gp_tasks = - rcu_preempt_ctrlblk.blkd_tasks.next; - - /* If there is no running reader, CPU is done with GP. */ - if (!rcu_preempt_running_reader()) - rcu_preempt_cpu_qs(); - } -} - -/* - * We have entered the scheduler, and the current task might soon be - * context-switched away from. If this task is in an RCU read-side - * critical section, we will no longer be able to rely on the CPU to - * record that fact, so we enqueue the task on the blkd_tasks list. - * If the task started after the current grace period began, as recorded - * by ->gpcpu, we enqueue at the beginning of the list. Otherwise - * before the element referenced by ->gp_tasks (or at the tail if - * ->gp_tasks is NULL) and point ->gp_tasks at the newly added element. - * The task will dequeue itself when it exits the outermost enclosing - * RCU read-side critical section. Therefore, the current grace period - * cannot be permitted to complete until the ->gp_tasks pointer becomes - * NULL. - * - * Caller must disable preemption. - */ -void rcu_preempt_note_context_switch(void) -{ - struct task_struct *t = current; - unsigned long flags; - - local_irq_save(flags); /* must exclude scheduler_tick(). */ - if (rcu_preempt_running_reader() && - (t->rcu_read_unlock_special & RCU_READ_UNLOCK_BLOCKED) == 0) { - - /* Possibly blocking in an RCU read-side critical section. */ - t->rcu_read_unlock_special |= RCU_READ_UNLOCK_BLOCKED; - - /* - * If this CPU has already checked in, then this task - * will hold up the next grace period rather than the - * current grace period. Queue the task accordingly. - * If the task is queued for the current grace period - * (i.e., this CPU has not yet passed through a quiescent - * state for the current grace period), then as long - * as that task remains queued, the current grace period - * cannot end. - */ - list_add(&t->rcu_node_entry, &rcu_preempt_ctrlblk.blkd_tasks); - if (rcu_cpu_blocking_cur_gp()) - rcu_preempt_ctrlblk.gp_tasks = &t->rcu_node_entry; - } - - /* - * Either we were not in an RCU read-side critical section to - * begin with, or we have now recorded that critical section - * globally. Either way, we can now note a quiescent state - * for this CPU. Again, if we were in an RCU read-side critical - * section, and if that critical section was blocking the current - * grace period, then the fact that the task has been enqueued - * means that current grace period continues to be blocked. - */ - rcu_preempt_cpu_qs(); - local_irq_restore(flags); -} - -/* - * Tiny-preemptible RCU implementation for rcu_read_lock(). - * Just increment ->rcu_read_lock_nesting, shared state will be updated - * if we block. - */ -void __rcu_read_lock(void) -{ - current->rcu_read_lock_nesting++; - barrier(); /* needed if we ever invoke rcu_read_lock in rcutiny.c */ -} -EXPORT_SYMBOL_GPL(__rcu_read_lock); - -/* - * Handle special cases during rcu_read_unlock(), such as needing to - * notify RCU core processing or task having blocked during the RCU - * read-side critical section. - */ -static void rcu_read_unlock_special(struct task_struct *t) -{ - int empty; - int empty_exp; - unsigned long flags; - struct list_head *np; - int special; - - /* - * NMI handlers cannot block and cannot safely manipulate state. - * They therefore cannot possibly be special, so just leave. - */ - if (in_nmi()) - return; - - local_irq_save(flags); - - /* - * If RCU core is waiting for this CPU to exit critical section, - * let it know that we have done so. - */ - special = t->rcu_read_unlock_special; - if (special & RCU_READ_UNLOCK_NEED_QS) - rcu_preempt_cpu_qs(); - - /* Hardware IRQ handlers cannot block. */ - if (in_irq()) { - local_irq_restore(flags); - return; - } - - /* Clean up if blocked during RCU read-side critical section. */ - if (special & RCU_READ_UNLOCK_BLOCKED) { - t->rcu_read_unlock_special &= ~RCU_READ_UNLOCK_BLOCKED; - - /* - * Remove this task from the ->blkd_tasks list and adjust - * any pointers that might have been referencing it. - */ - empty = !rcu_preempt_blocked_readers_cgp(); - empty_exp = rcu_preempt_ctrlblk.exp_tasks == NULL; - np = t->rcu_node_entry.next; - if (np == &rcu_preempt_ctrlblk.blkd_tasks) - np = NULL; - list_del(&t->rcu_node_entry); - if (&t->rcu_node_entry == rcu_preempt_ctrlblk.gp_tasks) - rcu_preempt_ctrlblk.gp_tasks = np; - if (&t->rcu_node_entry == rcu_preempt_ctrlblk.exp_tasks) - rcu_preempt_ctrlblk.exp_tasks = np; - INIT_LIST_HEAD(&t->rcu_node_entry); - - /* - * If this was the last task on the current list, and if - * we aren't waiting on the CPU, report the quiescent state - * and start a new grace period if needed. - */ - if (!empty && !rcu_preempt_blocked_readers_cgp()) { - rcu_preempt_cpu_qs(); - rcu_preempt_start_gp(); - } - - /* - * If this was the last task on the expedited lists, - * then we need wake up the waiting task. - */ - if (!empty_exp && rcu_preempt_ctrlblk.exp_tasks == NULL) - rcu_report_exp_done(); - } - local_irq_restore(flags); -} - -/* - * Tiny-preemptible RCU implementation for rcu_read_unlock(). - * Decrement ->rcu_read_lock_nesting. If the result is zero (outermost - * rcu_read_unlock()) and ->rcu_read_unlock_special is non-zero, then - * invoke rcu_read_unlock_special() to clean up after a context switch - * in an RCU read-side critical section and other special cases. - */ -void __rcu_read_unlock(void) -{ - struct task_struct *t = current; - - barrier(); /* needed if we ever invoke rcu_read_unlock in rcutiny.c */ - --t->rcu_read_lock_nesting; - barrier(); /* decrement before load of ->rcu_read_unlock_special */ - if (t->rcu_read_lock_nesting == 0 && - unlikely(ACCESS_ONCE(t->rcu_read_unlock_special))) - rcu_read_unlock_special(t); -#ifdef CONFIG_PROVE_LOCKING - WARN_ON_ONCE(t->rcu_read_lock_nesting < 0); -#endif /* #ifdef CONFIG_PROVE_LOCKING */ -} -EXPORT_SYMBOL_GPL(__rcu_read_unlock); - -/* - * Check for a quiescent state from the current CPU. When a task blocks, - * the task is recorded in the rcu_preempt_ctrlblk structure, which is - * checked elsewhere. This is called from the scheduling-clock interrupt. - * - * Caller must disable hard irqs. - */ -static void rcu_preempt_check_callbacks(void) -{ - struct task_struct *t = current; - - if (rcu_preempt_gp_in_progress() && - (!rcu_preempt_running_reader() || - !rcu_cpu_blocking_cur_gp())) - rcu_preempt_cpu_qs(); - if (&rcu_preempt_ctrlblk.rcb.rcucblist != - rcu_preempt_ctrlblk.rcb.donetail) - raise_softirq(RCU_SOFTIRQ); - if (rcu_preempt_gp_in_progress() && - rcu_cpu_blocking_cur_gp() && - rcu_preempt_running_reader()) - t->rcu_read_unlock_special |= RCU_READ_UNLOCK_NEED_QS; -} - -/* - * TINY_PREEMPT_RCU has an extra callback-list tail pointer to - * update, so this is invoked from __rcu_process_callbacks() to - * handle that case. Of course, it is invoked for all flavors of - * RCU, but RCU callbacks can appear only on one of the lists, and - * neither ->nexttail nor ->donetail can possibly be NULL, so there - * is no need for an explicit check. - */ -static void rcu_preempt_remove_callbacks(struct rcu_ctrlblk *rcp) -{ - if (rcu_preempt_ctrlblk.nexttail == rcp->donetail) - rcu_preempt_ctrlblk.nexttail = &rcp->rcucblist; -} - -/* - * Process callbacks for preemptible RCU. - */ -static void rcu_preempt_process_callbacks(void) -{ - __rcu_process_callbacks(&rcu_preempt_ctrlblk.rcb); -} - -/* - * Queue a preemptible -RCU callback for invocation after a grace period. - */ -void call_rcu(struct rcu_head *head, void (*func)(struct rcu_head *rcu)) -{ - unsigned long flags; - - debug_rcu_head_queue(head); - head->func = func; - head->next = NULL; - - local_irq_save(flags); - *rcu_preempt_ctrlblk.nexttail = head; - rcu_preempt_ctrlblk.nexttail = &head->next; - rcu_preempt_start_gp(); /* checks to see if GP needed. */ - local_irq_restore(flags); -} -EXPORT_SYMBOL_GPL(call_rcu); - -void rcu_barrier(void) -{ - struct rcu_synchronize rcu; - - init_rcu_head_on_stack(&rcu.head); - init_completion(&rcu.completion); - /* Will wake me after RCU finished. */ - call_rcu(&rcu.head, wakeme_after_rcu); - /* Wait for it. */ - wait_for_completion(&rcu.completion); - destroy_rcu_head_on_stack(&rcu.head); -} -EXPORT_SYMBOL_GPL(rcu_barrier); - -/* - * synchronize_rcu - wait until a grace period has elapsed. - * - * Control will return to the caller some time after a full grace - * period has elapsed, in other words after all currently executing RCU - * read-side critical sections have completed. RCU read-side critical - * sections are delimited by rcu_read_lock() and rcu_read_unlock(), - * and may be nested. - */ -void synchronize_rcu(void) -{ -#ifdef CONFIG_DEBUG_LOCK_ALLOC - if (!rcu_scheduler_active) - return; -#endif /* #ifdef CONFIG_DEBUG_LOCK_ALLOC */ - - WARN_ON_ONCE(rcu_preempt_running_reader()); - if (!rcu_preempt_blocked_readers_any()) - return; - - /* Once we get past the fastpath checks, same code as rcu_barrier(). */ - rcu_barrier(); -} -EXPORT_SYMBOL_GPL(synchronize_rcu); - -static DECLARE_WAIT_QUEUE_HEAD(sync_rcu_preempt_exp_wq); -static unsigned long sync_rcu_preempt_exp_count; -static DEFINE_MUTEX(sync_rcu_preempt_exp_mutex); - -/* - * Return non-zero if there are any tasks in RCU read-side critical - * sections blocking the current preemptible-RCU expedited grace period. - * If there is no preemptible-RCU expedited grace period currently in - * progress, returns zero unconditionally. - */ -static int rcu_preempted_readers_exp(void) -{ - return rcu_preempt_ctrlblk.exp_tasks != NULL; -} - -/* - * Report the exit from RCU read-side critical section for the last task - * that queued itself during or before the current expedited preemptible-RCU - * grace period. - */ -static void rcu_report_exp_done(void) -{ - wake_up(&sync_rcu_preempt_exp_wq); -} - -/* - * Wait for an rcu-preempt grace period, but expedite it. The basic idea - * is to rely in the fact that there is but one CPU, and that it is - * illegal for a task to invoke synchronize_rcu_expedited() while in a - * preemptible-RCU read-side critical section. Therefore, any such - * critical sections must correspond to blocked tasks, which must therefore - * be on the ->blkd_tasks list. So just record the current head of the - * list in the ->exp_tasks pointer, and wait for all tasks including and - * after the task pointed to by ->exp_tasks to drain. - */ -void synchronize_rcu_expedited(void) -{ - unsigned long flags; - struct rcu_preempt_ctrlblk *rpcp = &rcu_preempt_ctrlblk; - unsigned long snap; - - barrier(); /* ensure prior action seen before grace period. */ - - WARN_ON_ONCE(rcu_preempt_running_reader()); - - /* - * Acquire lock so that there is only one preemptible RCU grace - * period in flight. Of course, if someone does the expedited - * grace period for us while we are acquiring the lock, just leave. - */ - snap = sync_rcu_preempt_exp_count + 1; - mutex_lock(&sync_rcu_preempt_exp_mutex); - if (ULONG_CMP_LT(snap, sync_rcu_preempt_exp_count)) - goto unlock_mb_ret; /* Others did our work for us. */ - - local_irq_save(flags); - - /* - * All RCU readers have to already be on blkd_tasks because - * we cannot legally be executing in an RCU read-side critical - * section. - */ - - /* Snapshot current head of ->blkd_tasks list. */ - rpcp->exp_tasks = rpcp->blkd_tasks.next; - if (rpcp->exp_tasks == &rpcp->blkd_tasks) - rpcp->exp_tasks = NULL; - local_irq_restore(flags); - - /* Wait for tail of ->blkd_tasks list to drain. */ - if (rcu_preempted_readers_exp()) - wait_event(sync_rcu_preempt_exp_wq, - !rcu_preempted_readers_exp()); - - /* Clean up and exit. */ - barrier(); /* ensure expedited GP seen before counter increment. */ - sync_rcu_preempt_exp_count++; -unlock_mb_ret: - mutex_unlock(&sync_rcu_preempt_exp_mutex); - barrier(); /* ensure subsequent action seen after grace period. */ -} -EXPORT_SYMBOL_GPL(synchronize_rcu_expedited); - -/* - * Does preemptible RCU need the CPU to stay out of dynticks mode? - */ -int rcu_preempt_needs_cpu(void) -{ - if (!rcu_preempt_running_reader()) - rcu_preempt_cpu_qs(); - return rcu_preempt_ctrlblk.rcb.rcucblist != NULL; -} - -/* - * Check for a task exiting while in a preemptible -RCU read-side - * critical section, clean up if so. No need to issue warnings, - * as debug_check_no_locks_held() already does this if lockdep - * is enabled. - */ -void exit_rcu(void) -{ - struct task_struct *t = current; - - if (t->rcu_read_lock_nesting == 0) - return; - t->rcu_read_lock_nesting = 1; - rcu_read_unlock(); -} - -#else /* #ifdef CONFIG_TINY_PREEMPT_RCU */ - -/* - * Because preemptible RCU does not exist, it never has any callbacks - * to check. - */ -static void rcu_preempt_check_callbacks(void) -{ -} - -/* - * Because preemptible RCU does not exist, it never has any callbacks - * to remove. - */ -static void rcu_preempt_remove_callbacks(struct rcu_ctrlblk *rcp) -{ -} - -/* - * Because preemptible RCU does not exist, it never has any callbacks - * to process. - */ -static void rcu_preempt_process_callbacks(void) -{ -} - -#endif /* #else #ifdef CONFIG_TINY_PREEMPT_RCU */ - -#ifdef CONFIG_DEBUG_LOCK_ALLOC - -#include <linux/kernel_stat.h> - -/* - * During boot, we forgive RCU lockdep issues. After this function is - * invoked, we start taking RCU lockdep issues seriously. - */ -void rcu_scheduler_starting(void) -{ - WARN_ON(nr_context_switches() > 0); - rcu_scheduler_active = 1; -} - -#endif /* #ifdef CONFIG_DEBUG_LOCK_ALLOC */ |