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[Cluster-devel] [PATCH 1/6] GFS2: don't hold s_umount over blkdev_put

This is a GFS2 version of Tejun's patch:
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>

diff --git a/fs/gfs2/ops_fstype.c b/fs/gfs2/ops_fstype.c
index 82303b4..52fa883 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;

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