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

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>

diff --git a/drivers/md/bcache/super.c b/drivers/md/bcache/super.c
index 46a0013..b1a6ba9 100644 (file)
--- a/drivers/md/bcache/super.c
+++ b/drivers/md/bcache/super.c
@@ -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);

diff --git a/drivers/md/bcache/writeback.c b/drivers/md/bcache/writeback.c
index 3c74996..a129e4d 100644 (file)
--- 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;
                        }