On Tue, 2017-08-01 at 18:44 +0800, Ming Lei wrote: > On Mon, Jul 31, 2017 at 11:42:21PM +0000, Bart Van Assche wrote: > > Since setting, clearing and testing of BLK_MQ_S_BUSY can happen concurrently > > and since clearing and testing happens without any locks held I'm afraid this > > patch introduces the following race conditions: > > [ ... ] > > * Checking BLK_MQ_S_BUSY after requests have been removed from the dispatch list > > but before that bit is cleared, resulting in test_bit(BLK_MQ_S_BUSY, &hctx->state) > > reporting that the BLK_MQ_S_BUSY > > has been set although there are no requests > > on the dispatch list. > > That won't be a problem, because dispatch will be started in the > context in which dispatch list is flushed, since the BUSY bit > is cleared after blk_mq_dispatch_rq_list() returns. So no I/O > hang. Hello Ming, Please consider changing the name of the BLK_MQ_S_BUSY constant. That bit is used to serialize dispatching requests from the hctx dispatch list but that's not clear from the name of that constant. Thanks, Bart.
