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 (file)
--- 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 */

diff --git a/fs/super.c b/fs/super.c
index d8c8b1d..bc734f8 100644 (file)
--- a/fs/super.c
+++ b/fs/super.c
@@ -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;
 }

diff --git a/include/linux/fs.h b/include/linux/fs.h
index d13a6b8..62f84d9 100644 (file)
--- a/include/linux/fs.h
+++ b/include/linux/fs.h
@@ -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 */