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 <viro@zeniv.linux.org.uk>
diff --git a/fs/notify/inotify/inotify.c b/fs/notify/inotify/inotify.c
index 40b1cf9..441ef13 100644
--- a/fs/notify/inotify/inotify.c
+++ b/fs/notify/inotify/inotify.c
@@ -110,14 +110,10 @@
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 @@
* ->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 @@
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 */
diff --git a/fs/super.c b/fs/super.c
index d8c8b1d..bc734f8 100644
--- a/fs/super.c
+++ b/fs/super.c
@@ -93,7 +93,7 @@
* 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 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 @@
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 @@
*/
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;
}
diff --git a/include/linux/fs.h b/include/linux/fs.h
index d13a6b8..62f84d9 100644
--- a/include/linux/fs.h
+++ b/include/linux/fs.h
@@ -1314,7 +1314,6 @@
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 */
