From mboxrd@z Thu Jan 1 00:00:00 1970 From: Ming Lei Subject: Re: [PATCH] blk-mq: fix blk_mq_tagset_busy_iter Date: Fri, 3 Aug 2018 01:23:46 +0800 Message-ID: <20180802172345.GE8928@ming.t460p> References: <20180802164329.11900-1-ming.lei@redhat.com> <1533228846.3915.17.camel@HansenPartnership.com> <20180802170601.GC8928@ming.t460p> <1533230318.12916.2.camel@HansenPartnership.com> Mime-Version: 1.0 Content-Type: text/plain; charset=iso-8859-1 Content-Transfer-Encoding: 8bit Return-path: Content-Disposition: inline In-Reply-To: <1533230318.12916.2.camel@HansenPartnership.com> Sender: linux-kernel-owner@vger.kernel.org To: James Bottomley Cc: Jens Axboe , linux-block@vger.kernel.org, Josef Bacik , Christoph Hellwig , Guenter Roeck , Mark Brown , Matt Hart , Johannes Thumshirn , John Garry , Hannes Reinecke , "Martin K. Petersen" , linux-scsi@vger.kernel.org, linux-kernel@vger.kernel.org List-Id: linux-scsi@vger.kernel.org On Thu, Aug 02, 2018 at 10:18:38AM -0700, James Bottomley wrote: > On Thu, 2018-08-02 at 11:08 -0600, Jens Axboe wrote: > > On 8/2/18 11:06 AM, Ming Lei wrote: > > > On Thu, Aug 02, 2018 at 09:54:06AM -0700, James Bottomley wrote: > > > > On Fri, 2018-08-03 at 00:43 +0800, Ming Lei wrote: > > > > > Commit d250bf4e776ff09d5("blk-mq: only iterate over inflight > > > > > requests > > > > > in blk_mq_tagset_busy_iter") uses 'blk_mq_rq_state(rq) == > > > > > MQ_RQ_IN_FLIGHT' to replace 'blk_mq_request_started(req)', this > > > > > way is wrong, and causes lots of test system hang during > > > > > booting. > > > > > > > > > > Fix the issue by using blk_mq_request_started(req) inside > > > > > bt_tags_iter(). > > > > > > > > > > Fixes: d250bf4e776ff09d5 ("blk-mq: only iterate over inflight > > > > > requests in blk_mq_tagset_busy_iter") > > > > > Cc: Josef Bacik > > > > > Cc: Christoph Hellwig > > > > > Cc: Guenter Roeck > > > > > Cc: Mark Brown > > > > > Cc: Matt Hart > > > > > Cc: Johannes Thumshirn > > > > > Cc: John Garry > > > > > Cc: Hannes Reinecke , > > > > > Cc: "Martin K. Petersen" , > > > > > Cc: James Bottomley > > > > > Cc: linux-scsi@vger.kernel.org > > > > > Cc: linux-kernel@vger.kernel.org > > > > > Signed-off-by: Ming Lei > > > > > --- > > > > >  block/blk-mq-tag.c | 2 +- > > > > >  1 file changed, 1 insertion(+), 1 deletion(-) > > > > > > > > > > diff --git a/block/blk-mq-tag.c b/block/blk-mq-tag.c > > > > > index 09b2ee6694fb..3de0836163c2 100644 > > > > > --- a/block/blk-mq-tag.c > > > > > +++ b/block/blk-mq-tag.c > > > > > @@ -271,7 +271,7 @@ static bool bt_tags_iter(struct sbitmap > > > > > *bitmap, > > > > > unsigned int bitnr, void *data) > > > > >    * test and set the bit before assining ->rqs[]. > > > > >    */ > > > > >   rq = tags->rqs[bitnr]; > > > > > - if (rq && blk_mq_rq_state(rq) == MQ_RQ_IN_FLIGHT) > > > > > + if (rq && blk_mq_request_started(rq)) > > > > > > > > So now we have dueling versions of this patch: > > > > > > > > https://marc.info/?l=linux-scsi&m=153322802207688 > > > > > > > > Can we at least make sure we've root caused the problem and > > > > confirmed we've got it fixed before we start the formal patch > > > > process?  When we > > > > > > EH uses scsi_host_busy to check if the error handler needs to be > > > waken up. And blk_mq_tagset_busy_iter() is used for implementing > > > scsi_host_busy(), so causes EH not waken up, then this timed-out > > > request can't be handled. > > Yes, I know what the problem is and why this patch is necessary and > that it is very likely the root cause. However, can we confirm that it > fixes the boot hang completely before we declare victory? Frankly speaking, I can reproduce & verify it, but still suggest to wait for ack from our report guys. > > > > > do start the formal patch process, please give appropriate credit > > > > to the reporter(s) since this has been a royal pain for them to > > > > help us track down. > > > > > > Sure. > > > > > > Jens, could you add reported-by if you are fine with this version? > > > Or please just let me know if new version is needed, then I can add > > > it. > > > > I'll add that, would also love a tested-by from the reporter. The > > patch looks good to me, however. > > Is there a reason why blk_mq_request_started() isn't a static inline? > It looks to be somewhat in the hot path. Looks good idea, which should have been in header file, will do it in V2. Thanks, Ming