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Commit b20bd1a5 authored by Al Viro's avatar Al Viro
Browse files

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: default avatarAl Viro <viro@zeniv.linux.org.uk>
parent 389b8be6

fs/notify/inotify/inotify.c

+13 −19
Original line number Diff line number Diff line
@@ -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 */

fs/super.c

+11 −17
Original line number Diff line number Diff line
@@ -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)

{

	s->s_count++;

	if (atomic_inc_not_zero(&s->s_active)) {

		spin_unlock(&sb_lock);

		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;

	}

	/* 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);

	up_write(&s->s_umount);

	put_super(s);

	/* ... but in case it wasn't, let's at least yield() */

	yield();

	return 0;

}

include/linux/fs.h

+0 −1
Original line number Diff line number Diff line
@@ -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 */