bcache: fix race between setting bdev state to none and new write request direct to backing (df4ad532) · Commits · 戴 / test

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>

drivers/md/bcache/super.c

+0 −9

Original line number	Diff line number	Diff line
		@@ -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);

drivers/md/bcache/writeback.c

+9 −0

Original line number	Diff line number	Diff line
		@@ -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;
		}

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