From b20bd1a5e78af267dc4b6e1ffed48d5d776302c5 Mon Sep 17 00:00:00 2001 From: Al Viro Date: Mon, 22 Mar 2010 08:53:19 -0400 Subject: get rid of S_BIAS use atomic_inc_not_zero(&sb->s_active) instead of playing games with checking ->s_count > S_BIAS Signed-off-by: Al Viro --- fs/notify/inotify/inotify.c | 32 +++++++++++++------------------- 1 file changed, 13 insertions(+), 19 deletions(-) (limited to 'fs/notify/inotify/inotify.c') diff --git a/fs/notify/inotify/inotify.c b/fs/notify/inotify/inotify.c index 40b1cf914ccb..441ef136af22 100644 --- a/fs/notify/inotify/inotify.c +++ b/fs/notify/inotify/inotify.c @@ -110,14 +110,10 @@ EXPORT_SYMBOL_GPL(get_inotify_watch); int pin_inotify_watch(struct inotify_watch *watch) { struct super_block *sb = watch->inode->i_sb; - spin_lock(&sb_lock); - if (sb->s_count >= S_BIAS) { - atomic_inc(&sb->s_active); - spin_unlock(&sb_lock); + if (atomic_inc_not_zero(&sb->s_active)) { atomic_inc(&watch->count); return 1; } - spin_unlock(&sb_lock); return 0; } @@ -518,16 +514,16 @@ EXPORT_SYMBOL_GPL(inotify_init_watch); * ->s_umount, which will almost certainly wait until the superblock is shut * down and the watch in question is pining for fjords. That's fine, but * there is a problem - we might have hit the window between ->s_active - * getting to 0 / ->s_count - below S_BIAS (i.e. the moment when superblock - * is past the point of no return and is heading for shutdown) and the - * moment when deactivate_super() acquires ->s_umount. We could just do - * drop_super() yield() and retry, but that's rather antisocial and this - * stuff is luser-triggerable. OTOH, having grabbed ->s_umount and having - * found that we'd got there first (i.e. that ->s_root is non-NULL) we know - * that we won't race with inotify_umount_inodes(). So we could grab a - * reference to watch and do the rest as above, just with drop_super() instead - * of deactivate_super(), right? Wrong. We had to drop ih->mutex before we - * could grab ->s_umount. So the watch could've been gone already. + * getting to 0 (i.e. the moment when superblock is past the point of no return + * and is heading for shutdown) and the moment when deactivate_super() acquires + * ->s_umount. We could just do drop_super() yield() and retry, but that's + * rather antisocial and this stuff is luser-triggerable. OTOH, having grabbed + * ->s_umount and having found that we'd got there first (i.e. that ->s_root is + * non-NULL) we know that we won't race with inotify_umount_inodes(). So we + * could grab a reference to watch and do the rest as above, just with + * drop_super() instead of deactivate_super(), right? Wrong. We had to drop + * ih->mutex before we could grab ->s_umount. So the watch could've been gone + * already. * * That still can be dealt with - we need to save watch->wd, do idr_find() * and compare its result with our pointer. If they match, we either have @@ -565,14 +561,12 @@ static int pin_to_kill(struct inotify_handle *ih, struct inotify_watch *watch) struct super_block *sb = watch->inode->i_sb; s32 wd = watch->wd; - spin_lock(&sb_lock); - if (sb->s_count >= S_BIAS) { - atomic_inc(&sb->s_active); - spin_unlock(&sb_lock); + if (atomic_inc_not_zero(&sb->s_active)) { get_inotify_watch(watch); mutex_unlock(&ih->mutex); return 1; /* the best outcome */ } + spin_lock(&sb_lock); sb->s_count++; spin_unlock(&sb_lock); mutex_unlock(&ih->mutex); /* can't grab ->s_umount under it */ -- cgit v1.2.2