On Tue, 2018-04-10 at 21:55 +0800, Ming Lei wrote: > Then I have same question with Jianchao, what is the actual double > complete in linus tree between BLK_EH_RESET_TIMER and normal completion? > > Follows my understanding: > > 1) when timeout is detected on one request, its aborted_gstate is > updated in blk_mq_check_expired(). > > 2) run synchronize_rcu(), and make sure all pending completion is done > > 3) run blk_mq_rq_timed_out() > - ret = ops->timeout > - blk_mq_rq_update_aborted_gstate(req, 0) > - blk_add_timer(req); > > If normal completion is done between 1) and reset aborted_gstate in 3), > blk_mq_complete_request() will be called, and found that aborted_gstate > is set, then the rq won't be completed really. > > If normal completion is done after reset aborted_gstate in 3), it should > be same with applying this patch. Hello Ming, Please keep in mind that all synchronize_rcu() does is to wait for pre- existing RCU readers to finish. synchronize_rcu() does not prevent that new rcu_read_lock() calls happen. It is e.g. possible that after blk_mq_rq_update_aborted_gstate(req, 0) has been executed that a regular completion occurs. If that request is not reused before the timer that was restarted by the timeout code expires, that request will be completed twice. Bart.
