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

[Sasha Levin]

From: Dongsheng Yang <dongsheng.y...@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.y...@easystack.cn>
Signed-off-by: Coly Li <col...@suse.de>
Signed-off-by: Jens Axboe <ax...@kernel.dk>
Signed-off-by: Sasha Levin <sas...@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