freeze_bdev: kill bd_mount_sem

Now that we have the freeze count there is not much reason for bd_mount_sem
anymore.  The actual freeze/thaw operations are serialized using the
bd_fsfreeze_mutex, and the only other place we take bd_mount_sem is
get_sb_bdev which tries to prevent mounting a filesystem while the block
device is frozen.  Instead of add a check for bd_fsfreeze_count and
return -EBUSY if a filesystem is frozen.  While that is a change in user
visible behaviour a failing mount is much better for this case rather
than having the mount process stuck uninterruptible for a long time.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

1 files changed, 7 insertions, 2 deletions

diff --git a/fs/super.c b/fs/super.c
index 4906e2d8f400..1cb26a3e3df0 100644
--- a/fs/super.c
+++ b/fs/super.c
@@ -743,9 +743,14 @@ int get_sb_bdev(struct file_system_type *fs_type,
          * will protect the lockfs code from trying to start a snapshot
          * while we are mounting
          */
-        down(&bdev->bd_mount_sem);
+        mutex_lock(&bdev->bd_fsfreeze_mutex);
+        if (bdev->bd_fsfreeze_count > 0) {
+                mutex_unlock(&bdev->bd_fsfreeze_mutex);
+                error = -EBUSY;
+                goto error_bdev;
+        }
         s = sget(fs_type, test_bdev_super, set_bdev_super, bdev);
-        up(&bdev->bd_mount_sem);
+        mutex_unlock(&bdev->bd_fsfreeze_mutex);
         if (IS_ERR(s))
                 goto error_s;