From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Date: Fri, 27 Jul 2018 10:57:19 -0600 From: Keith Busch To: Bart Van Assche Cc: "hch@lst.de" , "ming.lei@redhat.com" , "linux-block@vger.kernel.org" , "martin.petersen@oracle.com" , "axboe@kernel.dk" , "jianchao.w.wang@oracle.com" Subject: Re: [PATCH 5/5] blk-mq: Rework blk-mq timeout handling again Message-ID: <20180727165718.GC20829@localhost.localdomain> References: <20180727162042.13425-1-bart.vanassche@wdc.com> <20180727162042.13425-6-bart.vanassche@wdc.com> <20180727164627.GB20829@localhost.localdomain> <08bd5d1c691e2c8f9950f7ebcf04716507a02675.camel@wdc.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii In-Reply-To: <08bd5d1c691e2c8f9950f7ebcf04716507a02675.camel@wdc.com> List-ID: On Fri, Jul 27, 2018 at 04:51:05PM +0000, Bart Van Assche wrote: > On Fri, 2018-07-27 at 10:46 -0600, Keith Busch wrote: > > On Fri, Jul 27, 2018 at 09:20:42AM -0700, Bart Van Assche wrote: > > > + ret = req->q->mq_ops->timeout(req, reserved); > > > + /* > > > + * BLK_EH_DONT_RESET_TIMER means that the block driver either > > > + * completed the request or still owns the request and will > > > + * continue processing the timeout asynchronously. In the > > > + * latter case, if blk_mq_complete_request() was called while > > > + * the timeout handler was in progress, ignore that call. > > > + */ > > > + if (ret == BLK_EH_DONT_RESET_TIMER) > > > + return; > > > > This is how completions get lost. > > The new approach for handling completions that occur while the .timeout() > callback in progress is as follows: > * blk_mq_complete_request() executes the following code: > if (blk_mq_change_rq_state(rq, MQ_RQ_TIMED_OUT, MQ_RQ_COMPLETE)) > return; > * blk_mq_rq_timed_out() executes the following code: > if (blk_mq_rq_state(req) == MQ_RQ_COMPLETE) { > __blk_mq_complete_request(req); > return; > } > > As one can see __blk_mq_complete_request() gets called if this race occurs. You skip that code if the driver returns BLK_EH_DONT_RESET_TIMER.