diff options
Diffstat (limited to 'fs/notify/mark.c')
| -rw-r--r-- | fs/notify/mark.c | 146 |
1 files changed, 75 insertions, 71 deletions
diff --git a/fs/notify/mark.c b/fs/notify/mark.c index 325185e514b..d90deaa08e7 100644 --- a/fs/notify/mark.c +++ b/fs/notify/mark.c @@ -20,28 +20,29 @@ * fsnotify inode mark locking/lifetime/and refcnting * * REFCNT: - * The mark->refcnt tells how many "things" in the kernel currently are - * referencing this object. The object typically will live inside the kernel - * with a refcnt of 2, one for each list it is on (i_list, g_list). Any task - * which can find this object holding the appropriete locks, can take a reference - * and the object itself is guarenteed to survive until the reference is dropped. + * The group->recnt and mark->refcnt tell how many "things" in the kernel + * currently are referencing the objects. Both kind of objects typically will + * live inside the kernel with a refcnt of 2, one for its creation and one for + * the reference a group and a mark hold to each other. + * If you are holding the appropriate locks, you can take a reference and the + * object itself is guaranteed to survive until the reference is dropped. * * LOCKING: - * There are 3 spinlocks involved with fsnotify inode marks and they MUST - * be taken in order as follows: + * There are 3 locks involved with fsnotify inode marks and they MUST be taken + * in order as follows: * + * group->mark_mutex * mark->lock - * group->mark_lock * inode->i_lock * - * mark->lock protects 2 things, mark->group and mark->inode. You must hold - * that lock to dereference either of these things (they could be NULL even with - * the lock) - * - * group->mark_lock protects the marks_list anchored inside a given group - * and each mark is hooked via the g_list. It also sorta protects the - * free_g_list, which when used is anchored by a private list on the stack of the - * task which held the group->mark_lock. + * group->mark_mutex protects the marks_list anchored inside a given group and + * each mark is hooked via the g_list. It also protects the groups private + * data (i.e group limits). + + * mark->lock protects the marks attributes like its masks and flags. + * Furthermore it protects the access to a reference of the group that the mark + * is assigned to as well as the access to a reference of the inode/vfsmount + * that is being watched by the mark. * * inode->i_lock protects the i_fsnotify_marks list anchored inside a * given inode and each mark is hooked via the i_list. (and sorta the @@ -64,18 +65,11 @@ * inode. We take i_lock and walk the i_fsnotify_marks safely. For each * mark on the list we take a reference (so the mark can't disappear under us). * We remove that mark form the inode's list of marks and we add this mark to a - * private list anchored on the stack using i_free_list; At this point we no - * longer fear anything finding the mark using the inode's list of marks. - * - * We can safely and locklessly run the private list on the stack of everything - * we just unattached from the original inode. For each mark on the private list - * we grab the mark-> and can thus dereference mark->group and mark->inode. If - * we see the group and inode are not NULL we take those locks. Now holding all - * 3 locks we can completely remove the mark from other tasks finding it in the - * future. Remember, 10 things might already be referencing this mark, but they - * better be holding a ref. We drop our reference we took before we unhooked it - * from the inode. When the ref hits 0 we can free the mark. - * + * private list anchored on the stack using i_free_list; we walk i_free_list + * and before we destroy the mark we make sure that we dont race with a + * concurrent destroy_group by getting a ref to the marks group and taking the + * groups mutex. + * Very similarly for freeing by group, except we use free_g_list. * * This has the very interesting property of being able to run concurrently with @@ -91,9 +85,8 @@ #include <linux/slab.h> #include <linux/spinlock.h> #include <linux/srcu.h> -#include <linux/writeback.h> /* for inode_lock */ -#include <asm/atomic.h> +#include <linux/atomic.h> #include <linux/fsnotify_backend.h> #include "fsnotify.h" @@ -110,8 +103,11 @@ void fsnotify_get_mark(struct fsnotify_mark *mark) void fsnotify_put_mark(struct fsnotify_mark *mark) { - if (atomic_dec_and_test(&mark->refcnt)) + if (atomic_dec_and_test(&mark->refcnt)) { + if (mark->group) + fsnotify_put_group(mark->group); mark->free_mark(mark); + } } /* @@ -119,14 +115,14 @@ void fsnotify_put_mark(struct fsnotify_mark *mark) * The caller had better be holding a reference to this mark so we don't actually * do the final put under the mark->lock */ -void fsnotify_destroy_mark(struct fsnotify_mark *mark) +void fsnotify_destroy_mark_locked(struct fsnotify_mark *mark, + struct fsnotify_group *group) { - struct fsnotify_group *group; struct inode *inode = NULL; - spin_lock(&mark->lock); + BUG_ON(!mutex_is_locked(&group->mark_mutex)); - group = mark->group; + spin_lock(&mark->lock); /* something else already called this function on this mark */ if (!(mark->flags & FSNOTIFY_MARK_FLAG_ALIVE)) { @@ -136,11 +132,6 @@ void fsnotify_destroy_mark(struct fsnotify_mark *mark) mark->flags &= ~FSNOTIFY_MARK_FLAG_ALIVE; - /* 1 from caller and 1 for being on i_list/g_list */ - BUG_ON(atomic_read(&mark->refcnt) < 2); - - spin_lock(&group->mark_lock); - if (mark->flags & FSNOTIFY_MARK_FLAG_INODE) { inode = mark->i.inode; fsnotify_destroy_inode_mark(mark); @@ -151,13 +142,22 @@ void fsnotify_destroy_mark(struct fsnotify_mark *mark) list_del_init(&mark->g_list); - spin_unlock(&group->mark_lock); spin_unlock(&mark->lock); + if (inode && (mark->flags & FSNOTIFY_MARK_FLAG_OBJECT_PINNED)) + iput(inode); + /* release lock temporarily */ + mutex_unlock(&group->mark_mutex); + spin_lock(&destroy_lock); list_add(&mark->destroy_list, &destroy_list); spin_unlock(&destroy_lock); wake_up(&destroy_waitq); + /* + * We don't necessarily have a ref on mark from caller so the above destroy + * may have actually freed it, unless this group provides a 'freeing_mark' + * function which must be holding a reference. + */ /* * Some groups like to know that marks are being freed. This is a @@ -179,16 +179,17 @@ void fsnotify_destroy_mark(struct fsnotify_mark *mark) * is just a lazy update (and could be a perf win...) */ - if (inode && (mark->flags & FSNOTIFY_MARK_FLAG_OBJECT_PINNED)) - iput(inode); + atomic_dec(&group->num_marks); - /* - * it's possible that this group tried to destroy itself, but this - * this mark was simultaneously being freed by inode. If that's the - * case, we finish freeing the group here. - */ - if (unlikely(atomic_dec_and_test(&group->num_marks))) - fsnotify_final_destroy_group(group); + mutex_lock_nested(&group->mark_mutex, SINGLE_DEPTH_NESTING); +} + +void fsnotify_destroy_mark(struct fsnotify_mark *mark, + struct fsnotify_group *group) +{ + mutex_lock_nested(&group->mark_mutex, SINGLE_DEPTH_NESTING); + fsnotify_destroy_mark_locked(mark, group); + mutex_unlock(&group->mark_mutex); } void fsnotify_set_mark_mask_locked(struct fsnotify_mark *mark, __u32 mask) @@ -213,26 +214,26 @@ void fsnotify_set_mark_ignored_mask_locked(struct fsnotify_mark *mark, __u32 mas * These marks may be used for the fsnotify backend to determine which * event types should be delivered to which group. */ -int fsnotify_add_mark(struct fsnotify_mark *mark, - struct fsnotify_group *group, struct inode *inode, - struct vfsmount *mnt, int allow_dups) +int fsnotify_add_mark_locked(struct fsnotify_mark *mark, + struct fsnotify_group *group, struct inode *inode, + struct vfsmount *mnt, int allow_dups) { int ret = 0; BUG_ON(inode && mnt); BUG_ON(!inode && !mnt); + BUG_ON(!mutex_is_locked(&group->mark_mutex)); /* * LOCKING ORDER!!!! + * group->mark_mutex * mark->lock - * group->mark_lock * inode->i_lock */ spin_lock(&mark->lock); - spin_lock(&group->mark_lock); - mark->flags |= FSNOTIFY_MARK_FLAG_ALIVE; + fsnotify_get_group(group); mark->group = group; list_add(&mark->g_list, &group->marks_list); atomic_inc(&group->num_marks); @@ -250,11 +251,8 @@ int fsnotify_add_mark(struct fsnotify_mark *mark, BUG(); } - spin_unlock(&group->mark_lock); - /* this will pin the object if appropriate */ fsnotify_set_mark_mask_locked(mark, mark->mask); - spin_unlock(&mark->lock); if (inode) @@ -264,10 +262,10 @@ int fsnotify_add_mark(struct fsnotify_mark *mark, err: mark->flags &= ~FSNOTIFY_MARK_FLAG_ALIVE; list_del_init(&mark->g_list); + fsnotify_put_group(group); mark->group = NULL; atomic_dec(&group->num_marks); - spin_unlock(&group->mark_lock); spin_unlock(&mark->lock); spin_lock(&destroy_lock); @@ -278,6 +276,16 @@ err: return ret; } +int fsnotify_add_mark(struct fsnotify_mark *mark, struct fsnotify_group *group, + struct inode *inode, struct vfsmount *mnt, int allow_dups) +{ + int ret; + mutex_lock(&group->mark_mutex); + ret = fsnotify_add_mark_locked(mark, group, inode, mnt, allow_dups); + mutex_unlock(&group->mark_mutex); + return ret; +} + /* * clear any marks in a group in which mark->flags & flags is true */ @@ -285,22 +293,16 @@ void fsnotify_clear_marks_by_group_flags(struct fsnotify_group *group, unsigned int flags) { struct fsnotify_mark *lmark, *mark; - LIST_HEAD(free_list); - spin_lock(&group->mark_lock); + mutex_lock_nested(&group->mark_mutex, SINGLE_DEPTH_NESTING); list_for_each_entry_safe(mark, lmark, &group->marks_list, g_list) { if (mark->flags & flags) { - list_add(&mark->free_g_list, &free_list); - list_del_init(&mark->g_list); fsnotify_get_mark(mark); + fsnotify_destroy_mark_locked(mark, group); + fsnotify_put_mark(mark); } } - spin_unlock(&group->mark_lock); - - list_for_each_entry_safe(mark, lmark, &free_list, free_g_list) { - fsnotify_destroy_mark(mark); - fsnotify_put_mark(mark); - } + mutex_unlock(&group->mark_mutex); } /* @@ -316,6 +318,8 @@ void fsnotify_duplicate_mark(struct fsnotify_mark *new, struct fsnotify_mark *ol assert_spin_locked(&old->lock); new->i.inode = old->i.inode; new->m.mnt = old->m.mnt; + if (old->group) + fsnotify_get_group(old->group); new->group = old->group; new->mask = old->mask; new->free_mark = old->free_mark; @@ -336,7 +340,7 @@ void fsnotify_init_mark(struct fsnotify_mark *mark, static int fsnotify_mark_destroy(void *ignored) { struct fsnotify_mark *mark, *next; - LIST_HEAD(private_destroy_list); + struct list_head private_destroy_list; for (;;) { spin_lock(&destroy_lock); |