From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Date: Sat, 2 Dec 2017 09:00:26 +0800 From: Ming Lei To: Bart Van Assche Cc: "hch@lst.de" , "jthumshirn@suse.de" , "hare@suse.de" , "linux-block@vger.kernel.org" , "osandov@fb.com" , "axboe@kernel.dk" Subject: Re: [PATCH 4/7] blk-mq: Avoid that request processing stalls when sharing tags Message-ID: <20171202010026.GC24521@ming.t460p> References: <20171201000848.2656-1-bart.vanassche@wdc.com> <20171201000848.2656-5-bart.vanassche@wdc.com> <20171201025803.GA29741@ming.t460p> <1512157932.2520.27.camel@wdc.com> <20171202003625.GA24521@ming.t460p> <1512175730.2520.29.camel@wdc.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii In-Reply-To: <1512175730.2520.29.camel@wdc.com> List-ID: On Sat, Dec 02, 2017 at 12:48:51AM +0000, Bart Van Assche wrote: > On Sat, 2017-12-02 at 08:36 +0800, Ming Lei wrote: > > On Fri, Dec 01, 2017 at 07:52:14PM +0000, Bart Van Assche wrote: > > > On Fri, 2017-12-01 at 10:58 +0800, Ming Lei wrote: > > > > On Thu, Nov 30, 2017 at 04:08:45PM -0800, Bart Van Assche wrote: > > > > > blk_mq_dispatch_rq_list() is called. Make sure that > > > > > BLK_MQ_S_SCHED_RESTART is set before any blk_mq_dispatch_rq_list() > > > > > call occurs. > > > > > > > > > > Fixes: commit b347689ffbca ("blk-mq-sched: improve dispatching from sw queue") > > > > > > > > We always mark RESTART state bit just before dispatching from ->dispatch_list, > > > > this way has been there before b347689ffbca, which doesn't change this > > > > RESTART mechanism, so please explain a bit why it is a fix on commit > > > > b347689ffbca. > > > > > > I'm not completely sure which patch introduced the lockup fixed by this patch > > > but I will have another look whether this was really introduced by commit > > > b347689ffbca. > > > > Please make sure 'Fixes' tag correct. > > Further tests have shown that the lockup I referred to does not occur before commit > b347689ffbca but that it occurs with b347689ffbca. Then you need to root cause it, or Provide debugfs log and reproduction steps, please. > I think that shows clearly that commit b347689ffbca introduced this lockup. That may not be so clearly, maybe it is just triggered easily after this commit. -- Ming