btrfs: fix mount/umount race

Do *NOT* skip doomed superblocks in btrfs_test_super(); we want
sget() to wait for their shutdown to complete.  Since we don't
mutilate ->s_fs_info in ->put_super() anymore (or free what it
used to point to until the superblock is past being findable
by sget()), we can just DTRT there and report a match.

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

1 files changed, 4 insertions, 9 deletions

diff --git a/fs/btrfs/super.c b/fs/btrfs/super.c
index eca48624a4f0..b9fd62a0fca2 100644
--- a/fs/btrfs/super.c
+++ b/fs/btrfs/super.c
@@ -733,20 +733,15 @@ static int btrfs_test_super(struct super_block *s, void *data)
         struct btrfs_root *test_root = data;
         struct btrfs_root *root = btrfs_sb(s);
 
-        /*
-         * If this super block is going away, return false as it
-         * can't match as an existing super block.
-         */
-        if (!atomic_read(&s->s_active))
-                return 0;
         return root->fs_info->fs_devices == test_root->fs_info->fs_devices;
 }
 
 static int btrfs_set_super(struct super_block *s, void *data)
 {
-        s->s_fs_info = data;
-
-        return set_anon_super(s, data);
+        int err = set_anon_super(s, data);
+        if (!err)
+                s->s_fs_info = data;
+        return err;
 }
 
 /*