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

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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>
This commit is contained in:
Dongsheng Yang 2020-12-08 00:39:15 +08:00 committed by Jens Axboe
parent 733c15bd3a
commit df4ad53242
2 changed files with 9 additions and 9 deletions
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9
drivers/md/bcache/super.c
View file

@ -1114,9 +1114,6 @@ 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));
@ -1130,12 +1127,6 @@ 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);

9
drivers/md/bcache/writeback.c
View file

@ -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;
}