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

From: Steven Whitehouse
Date: Thu Jan 02 2014 - 07:29:07 EST

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@xxxxxxxxxx>
Reported-by: Al Viro <viro@xxxxxxxxxxxxxxxxxx>
Signed-off-by: Steven Whitehouse <swhiteho@xxxxxxxxxx>

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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