A fresh backing device is not attached to any cache_set, and has no writeback kthread created until first attached to some cache_set. But bch_cached_dev_writeback_init run " dc->writeback_running = true; WARN_ON(test_and_clear_bit(BCACHE_DEV_WB_RUNNING, &dc->disk.flags)); " for any newly formatted backing devices. For a fresh standalone backing device, we can get something like following even if no writeback kthread created: ------------------------ /sys/block/bcache0/bcache# cat writeback_running 1 /sys/block/bcache0/bcache# cat writeback_rate_debug rate: 512.0k/sec dirty: 0.0k target: 0.0k proportional: 0.0k integral: 0.0k change: 0.0k/sec next io: -15427384ms The none ZERO fields are misleading as no alive writeback kthread yet. Set dc->writeback_running to false as no writeback thread created in bch_cached_dev_writeback_init(). We have writeback thread created and woken up in bch_cached_dev_writeback _start(). Set dc->writeback_running to true after bch_writeback_queue() called. After the change, we can get the following output for a fresh standalone backing device: ----------------------- /sys/block/bcache0/bcache$ cat writeback_running 0 /sys/block/bcache0/bcache# cat writeback_rate_debug rate: 0.0k/sec dirty: 0.0k target: 0.0k proportional: 0.0k integral: 0.0k change: 0.0k/sec next io: 0ms Signed-off-by: Shenghui Wang <shhuiw@xxxxxxxxxxx> --- drivers/md/bcache/writeback.c | 3 ++- 1 file changed, 2 insertions(+), 1 deletion(-) diff --git a/drivers/md/bcache/writeback.c b/drivers/md/bcache/writeback.c index 08c3a9f9676c..81263bbc1608 100644 --- a/drivers/md/bcache/writeback.c +++ b/drivers/md/bcache/writeback.c @@ -777,7 +777,7 @@ void bch_cached_dev_writeback_init(struct cached_dev *dc) bch_keybuf_init(&dc->writeback_keys); dc->writeback_metadata = true; - dc->writeback_running = true; + dc->writeback_running = false; dc->writeback_percent = 10; dc->writeback_delay = 30; atomic_long_set(&dc->writeback_rate.rate, 1024); @@ -811,6 +811,7 @@ int bch_cached_dev_writeback_start(struct cached_dev *dc) dc->writeback_rate_update_seconds * HZ); bch_writeback_queue(dc); + dc->writeback_running = true; return 0; } -- 2.18.0
