Btrfs: fix use-after-free problem of the device during device replace

The problem is:
	Task0(device scan task)		Task1(device replace task)
	scan_one_device()
	mutex_lock(&uuid_mutex)
	device = find_device()
					mutex_lock(&device_list_mutex)
					lock_chunk()
					rm_and_free_source_device
					unlock_chunk()
					mutex_unlock(&device_list_mutex)
	check device

Destroying the target device if device replace fails also has the same problem.

We fix this problem by locking uuid_mutex during destroying source device or
target device, just like the device remove operation.

It is a temporary solution, we can fix this problem and make the code more
clear by atomic counter in the future.

Signed-off-by: Miao Xie <miaox@cn.fujitsu.com>
Signed-off-by: Chris Mason <clm@fb.com>

1 files changed, 2 insertions, 0 deletions

diff --git a/fs/btrfs/volumes.h b/fs/btrfs/volumes.h
index 76600a3fedbe..2b37da3dd408 100644
--- a/fs/btrfs/volumes.h
+++ b/fs/btrfs/volumes.h
@@ -24,6 +24,8 @@
 #include <linux/btrfs.h>
 #include "async-thread.h"
 
+extern struct mutex uuid_mutex;
+
 #define BTRFS_STRIPE_LEN	(64 * 1024)
 
 struct buffer_head;