[PATCH AUTOSEL 5.4 093/130] bcache: fix race between setting bdev state to none and new write request direct to backing

Sasha Levin
2020-12-23T02:56:37Z

From: Dongsheng Yang <dongsheng.yang@easystack.cn>

[ Upstream commit df4ad53242158f9f1f97daf4feddbb4f8b77f080 ]

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>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
drivers/md/bcache/super.c | 9 ---------
drivers/md/bcache/writeback.c | 9 +++++++++
2 files changed, 9 insertions(+), 9 deletions(-)

diff --git a/drivers/md/bcache/super.c b/drivers/md/bcache/super.c
index 63f5ce18311bb..a251c1f35afa9 100644
--- a/drivers/md/bcache/super.c
+++ b/drivers/md/bcache/super.c
@@ -1040,9 +1040,6 @@ static void cancel_writeback_rate_update_dwork(struct cached_dev *dc)
static void cached_dev_detach_finish(struct work_struct *w)
{
struct cached_dev *dc = container_of(w, struct cached_dev, detach);
- struct closure cl;
-
- closure_init_stack(&cl);

BUG_ON(!test_bit(BCACHE_DEV_DETACHING, &dc->disk.flags));
BUG_ON(refcount_read(&dc->count));
@@ -1056,12 +1053,6 @@ static void cached_dev_detach_finish(struct work_struct *w)
dc->writeback_thread = NULL;
}

- memset(&dc->sb.set_uuid, 0, 16);
- SET_BDEV_STATE(&dc->sb, BDEV_STATE_NONE);
-
- bch_write_bdev_super(dc, &cl);
- closure_sync(&cl);
-
mutex_lock(&bch_register_lock);

calc_cached_dev_sectors(dc->disk.c);
diff --git a/drivers/md/bcache/writeback.c b/drivers/md/bcache/writeback.c
index 0b02210ab4355..38b5c6cc18c7b 100644
--- a/drivers/md/bcache/writeback.c
+++ b/drivers/md/bcache/writeback.c
@@ -703,6 +703,15 @@ 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;
}
--
2.27.0