Saner locking around deactivate_super()

[safe/jmp/linux-2.6] / fs / super.c

diff --git a/fs/super.c b/fs/super.c
index bc734f8..157657b 100644 (file)
--- a/fs/super.c
+++ b/fs/super.c
@@ -178,53 +178,48 @@ void put_super(struct super_block *sb)
 
 
 /**
- *     deactivate_super        -       drop an active reference to superblock
+ *     deactivate_locked_super -       drop an active reference to superblock
  *     @s: superblock to deactivate
  *
- *     Drops an active reference to superblock, acquiring a temprory one if
- *     there is no active references left.  In that case we lock superblock,
+ *     Drops an active reference to superblock, converting it into a temprory
+ *     one if there is no other active references left.  In that case we
  *     tell fs driver to shut it down and drop the temporary reference we
  *     had just acquired.
+ *
+ *     Caller holds exclusive lock on superblock; that lock is released.
  */
-void deactivate_super(struct super_block *s)
+void deactivate_locked_super(struct super_block *s)
 {
        struct file_system_type *fs = s->s_type;
        if (atomic_dec_and_test(&s->s_active)) {
                vfs_dq_off(s, 0);
-               down_write(&s->s_umount);
                fs->kill_sb(s);
                put_filesystem(fs);
                put_super(s);
+       } else {
+               up_write(&s->s_umount);
        }
 }
 
-EXPORT_SYMBOL(deactivate_super);
+EXPORT_SYMBOL(deactivate_locked_super);
 
 /**
- *     deactivate_locked_super -       drop an active reference to superblock
+ *     deactivate_super        -       drop an active reference to superblock
  *     @s: superblock to deactivate
  *
- *     Equivalent of up_write(&s->s_umount); deactivate_super(s);, except that
- *     it does not unlock it until it's all over.  As the result, it's safe to
- *     use to dispose of new superblock on ->get_sb() failure exits - nobody
- *     will see the sucker until it's all over.  Equivalent using up_write +
- *     deactivate_super is safe for that purpose only if superblock is either
- *     safe to use or has NULL ->s_root when we unlock.
+ *     Variant of deactivate_locked_super(), except that superblock is *not*
+ *     locked by caller.  If we are going to drop the final active reference,
+ *     lock will be acquired prior to that.
  */
-void deactivate_locked_super(struct super_block *s)
+void deactivate_super(struct super_block *s)
 {
-       struct file_system_type *fs = s->s_type;
-       if (atomic_dec_and_test(&s->s_active)) {
-               vfs_dq_off(s, 0);
-               fs->kill_sb(s);
-               put_filesystem(fs);
-               put_super(s);
-       } else {
-               up_write(&s->s_umount);
+        if (!atomic_add_unless(&s->s_active, -1, 1)) {
+               down_write(&s->s_umount);
+               deactivate_locked_super(s);
        }
 }
 
-EXPORT_SYMBOL(deactivate_locked_super);
+EXPORT_SYMBOL(deactivate_super);
 
 /**
  *     grab_super - acquire an active reference
@@ -247,12 +242,10 @@ static int grab_super(struct super_block *s) __releases(sb_lock)
        /* it's going away */
        s->s_count++;
        spin_unlock(&sb_lock);
-       /* usually that'll be enough for it to die... */
+       /* wait 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;
 }