From: Tang Junhui <[email protected]>
Hello Coly,
>When cache set is stopping, calculating writeback rate is wast of time.
>This is the purpose of the first checking, to avoid unnecessary delay
>from bcache_flash_devs_sectors_dirty() inside __update_writeback_rate().
I thought twice, and found there is still a race.
work update_writeback_rate is runing:
>@@ -91,6 +91,11 @@ static void update_writeback_rate(struct work_struct *work)
> struct cached_dev *dc = container_of(to_delayed_work(work),
> struct cached_dev,
> writeback_rate_update);
>+ struct cache_set *c = dc->disk.c;
>+
>+ /* quit directly if cache set is stopping */
>+ if (test_bit(CACHE_SET_STOPPING, &c->flags))
>+ return;
>
> down_read(&dc->writeback_lock);
>
>@@ -100,6 +105,10 @@ static void update_writeback_rate(struct work_struct
>*work)
>
> up_read(&dc->writeback_lock);
>
>+ /* do not schedule delayed work if cache set is stopping */
>+ if (test_bit(CACHE_SET_STOPPING, &c->flags))
>+ return;
>+
and if cancel_delayed_wsrksync() runs at this moment, the code can not prevent
the
work re-arming itself to workqueue. So maybe we need a locker to protect it.
> schedule_delayed_work(&dc->writeback_rate_update,
> dc->writeback_rate_update_seconds * HZ);
> }
Thanks,
Tang Junhui
