On 12/17/2015 05:33 PM, Tejun Heo wrote: > Hello, Nikolay. > > On Thu, Dec 17, 2015 at 12:46:10PM +0200, Nikolay Borisov wrote: >> diff --git a/drivers/md/dm-thin.c b/drivers/md/dm-thin.c >> index 493c38e08bd2..ccbbf7823cf3 100644 >> --- a/drivers/md/dm-thin.c >> +++ b/drivers/md/dm-thin.c >> @@ -3506,8 +3506,8 @@ static void pool_postsuspend(struct dm_target *ti) >> struct pool_c *pt = ti->private; >> struct pool *pool = pt->pool; >> >> - cancel_delayed_work(&pool->waker); >> - cancel_delayed_work(&pool->no_space_timeout); >> + cancel_delayed_work_sync(&pool->waker); >> + cancel_delayed_work_sync(&pool->no_space_timeout); >> flush_workqueue(pool->wq); >> (void) commit(pool); >> } >> >> And this seems to have resolved the crashes. For the past 24 hours I >> haven't seen a single server crash whereas before at least 3-5 servers >> would crash. > > So, that's an obvious bug on dm-thin side. Mike if you are ok with this I will submit a proper patch ? > >> Given that, it seems like a race condition between destroying the >> workqueue from dm-thin and cancelling all the delayed work. >> >> Tejun, I've looked at cancel_delayed_work/cancel_delayed_work_sync and >> they both call try_to_grab_pending and then their function diverges. Is >> it possible that there is a latent race condition between canceling the >> delayed work and the subsequent re-scheduling of the work item? > > It's just the wrong variant being used. cancel_delayed_work() doesn't > guarantee that the work item isn't running on return. If the work > item was running and the workqueue is destroyed afterwards, it may end > up trying to requeue itself on a destroyed workqueue. Right, but my initial understanding was that when canceling the delayed work and then issuing flush_workqueue would act the same way as if cancel_delayed_work_sync is called wrt to this particular delayed item, no? > > Thanks. > -- dm-devel mailing list dm-devel@xxxxxxxxxx https://www.redhat.com/mailman/listinfo/dm-devel
