GFS2: don't hold s_umount over blkdev_put

This is a GFS2 version of Tejun's patch:
4f331f01b9c43bf001d3ffee578a97a1e0633eac
vfs: don't hold s_umount over close_bdev_exclusive() call

In this case its blkdev_put itself that is the issue and this
patch uses the same solution of dropping and retaking s_umount.

Reported-by: Tejun Heo <tj@kernel.org>
Reported-by: Al Viro <viro@ZenIV.linux.org.uk>
Signed-off-by: Steven Whitehouse <swhiteho@redhat.com>

1 files changed, 11 insertions, 1 deletions

diff --git a/fs/gfs2/ops_fstype.c b/fs/gfs2/ops_fstype.c
index 82303b474958..52fa88314f5c 100644
--- a/fs/gfs2/ops_fstype.c
+++ b/fs/gfs2/ops_fstype.c
@@ -1366,8 +1366,18 @@ static struct dentry *gfs2_mount(struct file_system_type *fs_type, int flags,
         if (IS_ERR(s))
                 goto error_bdev;
 
-        if (s->s_root)
+        if (s->s_root) {
+                /*
+                 * s_umount nests inside bd_mutex during
+                 * __invalidate_device().  blkdev_put() acquires
+                 * bd_mutex and can't be called under s_umount.  Drop
+                 * s_umount temporarily.  This is safe as we're
+                 * holding an active reference.
+                 */
+                up_write(&s->s_umount);
                 blkdev_put(bdev, mode);
+                down_write(&s->s_umount);
+        }
 
         memset(&args, 0, sizeof(args));
         args.ar_quota = GFS2_QUOTA_DEFAULT;