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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
View file

@ -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 */

28
fs/super.c
View file

@ -93,7 +93,7 @@ static struct super_block *alloc_super(struct file_system_type *type)
* subclass.
*/
down_write_nested(&s->s_umount, SINGLE_DEPTH_NESTING);
s->s_count = S_BIAS;
s->s_count = 1;
atomic_set(&s->s_active, 1);
mutex_init(&s->s_vfs_rename_mutex);
mutex_init(&s->s_dquot.dqio_mutex);
@ -189,9 +189,7 @@ void put_super(struct super_block *sb)
void deactivate_super(struct super_block *s)
{
struct file_system_type *fs = s->s_type;
if (atomic_dec_and_lock(&s->s_active, &sb_lock)) {
s->s_count -= S_BIAS-1;
spin_unlock(&sb_lock);
if (atomic_dec_and_test(&s->s_active)) {
vfs_dq_off(s, 0);
down_write(&s->s_umount);
fs->kill_sb(s);
@ -216,9 +214,7 @@ EXPORT_SYMBOL(deactivate_super);
void deactivate_locked_super(struct super_block *s)
{
struct file_system_type *fs = s->s_type;
if (atomic_dec_and_lock(&s->s_active, &sb_lock)) {
s->s_count -= S_BIAS-1;
spin_unlock(&sb_lock);
if (atomic_dec_and_test(&s->s_active)) {
vfs_dq_off(s, 0);
fs->kill_sb(s);
put_filesystem(fs);
@ -243,21 +239,19 @@ EXPORT_SYMBOL(deactivate_locked_super);
*/
static int grab_super(struct super_block *s) __releases(sb_lock)
{
if (atomic_inc_not_zero(&s->s_active)) {
spin_unlock(&sb_lock);
down_write(&s->s_umount);
return 1;
}
/* it's going away */
s->s_count++;
spin_unlock(&sb_lock);
/* usually that'll be enough for it to die... */
down_write(&s->s_umount);
if (s->s_root) {
spin_lock(&sb_lock);
if (s->s_count > S_BIAS) {
atomic_inc(&s->s_active);
s->s_count--;
spin_unlock(&sb_lock);
return 1;
}
spin_unlock(&sb_lock);
}
up_write(&s->s_umount);
put_super(s);
/* ... but in case it wasn't, let's at least yield() */
yield();
return 0;
}

1
include/linux/fs.h
View file

@ -1314,7 +1314,6 @@ extern int send_sigurg(struct fown_struct *fown);
extern struct list_head super_blocks;
extern spinlock_t sb_lock;
#define S_BIAS (1<<30)
struct super_block {
struct list_head s_list; /* Keep this first */
dev_t s_dev; /* search index; _not_ kdev_t */