From 3d07b06c5d62e98b46ef21980e5c2a904990149f Mon Sep 17 00:00:00 2001
From: Kyle McMartin <kyle@mcmartin.ca>
Date: Fri, 10 Dec 2010 10:32:29 -0500
Subject: [PATCH] Btrfs - fix race between btrfs_get_sb() and umount

When mounting a btrfs file system btrfs_test_super() may attempt to
use sb->s_fs_info, the btrfs root, of a super block that is going away
and that has had the btrfs root set to NULL in its ->put_super(). But
if the super block is going away it cannot be an existing super block
so we can return false in this case.

Signed-off-by: Ian Kent <raven@themaw.net>
Signed-off-by: Chris Mason <chris.mason@oracle.com>

Conflicts:

	fs/btrfs/super.c
---
 fs/btrfs/super.c |    6 ++++++
 1 files changed, 6 insertions(+), 0 deletions(-)

diff --git a/fs/btrfs/super.c b/fs/btrfs/super.c
index 89e299f..f4a4dd3 100644
--- a/fs/btrfs/super.c
+++ b/fs/btrfs/super.c
@@ -551,6 +551,12 @@ 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;
 }
 
-- 
1.7.3.3