bcache: fix race between setting bdev state to none and new write request direct to backing

There is a race condition in detaching as below:
A. detaching			B. Write request
(1) writing back
(2) write back done, set bdev
    state to clean.
(3) cached_dev_put() and
    schedule_work(&dc->detach);
				(4) write data [0 - 4K] directly
				    into backing and ack to user.
(5) power-failure...

When we restart this bcache device, this bdev is clean but not detached,
and read [0 - 4K], we will get unexpected old data from cache device.

To fix this problem, set the bdev state to none when we writeback done
in detaching, and then if power-failure happened as above, the data in
cache will not be used in next bcache device starting, it's detached, we
will read the correct data from backing derectly.

Signed-off-by: Dongsheng Yang <dongsheng.yang@easystack.cn>
Signed-off-by: Coly Li <colyli@suse.de>
Signed-off-by: Jens Axboe <axboe@kernel.dk>

1 files changed, 9 insertions, 0 deletions

diff --git a/drivers/md/bcache/writeback.c b/drivers/md/bcache/writeback.c
index 3c74996978da..a129e4d2707c 100644
--- a/drivers/md/bcache/writeback.c
+++ b/drivers/md/bcache/writeback.c
@@ -705,6 +705,15 @@ static int bch_writeback_thread(void *arg)
 			 * bch_cached_dev_detach().
 			 */
 			if (test_bit(BCACHE_DEV_DETACHING, &dc->disk.flags)) {
+				struct closure cl;
+
+				closure_init_stack(&cl);
+				memset(&dc->sb.set_uuid, 0, 16);
+				SET_BDEV_STATE(&dc->sb, BDEV_STATE_NONE);
+
+				bch_write_bdev_super(dc, &cl);
+				closure_sync(&cl);
+
 				up_write(&dc->writeback_lock);
 				break;
 			}