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get rid of S_BIAS

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use atomic_inc_not_zero(&sb->s_active) instead of playing games with
checking ->s_count > S_BIAS

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
This commit is contained in:
Al Viro
2010-03-22 08:53:19 -04:00
parent 389b8be6ef
commit b20bd1a5e7
3 changed files with 24 additions and 37 deletions
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32
fs/notify/inotify/inotify.c
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@@ -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 */