linux-kernel - Re: [PATCH] blk-mq: Directly schedule q->timeout

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Date:   Tue, 10 Apr 2018 22:46:07 +0200
From:   Martin Steigerwald <martin@...htvoll.de>
To:     Martin Steigerwald <martin@...htvoll.de>
Cc:     Tejun Heo <tj@...nel.org>, Sitsofe Wheeler <sitsofe@...il.com>,
        Jens Axboe <axboe@...nel.dk>, linux-kernel@...r.kernel.org,
        linux-block@...r.kernel.org,
        Stefan Haberland <sth@...ux.vnet.ibm.com>,
        Jan Hoeppner <hoeppner@...ux.vnet.ibm.com>,
        Bart Van Assche <Bart.VanAssche@....com>
Subject: Re: [PATCH] blk-mq: Directly schedule q->timeout_work when aborting a request

Martin Steigerwald - 10.04.18, 20:43:
> Tejun Heo - 03.04.18, 00:04:
> > Request abortion is performed by overriding deadline to now and
> > scheduling timeout handling immediately.  For the latter part, the
> > code was using mod_timer(timeout, 0) which can't guarantee that the
> > timer runs afterwards.  Let's schedule the underlying work item
> > directly instead.
> > 
> > This fixes the hangs during probing reported by Sitsofe but it isn't
> > yet clear to me how the failure can happen reliably if it's just the
> > above described race condition.
> 
> Compiling a 4.16.1 kernel with that patch to test whether this fixes
> the boot hang I reported in:
> 
> [Possible REGRESSION, 4.16-rc4] Error updating SMART data during
> runtime and boot failures with blk_mq_terminate_expired in backtrace
> https://bugzilla.kernel.org/show_bug.cgi?id=199077

Fails as well, see

https://bugzilla.kernel.org/show_bug.cgi?id=199077#c8

for photo with (part of) backtrace.

> The "Error updating SMART data during runtime" thing I reported there
> as well may still be another (independent) issue.
> 
> > Signed-off-by: Tejun Heo <tj@...nel.org>
> > Reported-by: Sitsofe Wheeler <sitsofe@...il.com>
> > Reported-by: Meelis Roos <mroos@...ux.ee>
> > Fixes: 358f70da49d7 ("blk-mq: make blk_abort_request() trigger
> > timeout path") Cc: stable@...r.kernel.org # v4.16
> > Link:
> > http://lkml.kernel.org/r/CALjAwxh-PVYFnYFCJpGOja+m5SzZ8Sa4J7ohxdK=r8
> > NyOF-EM A@...l.gmail.com Link:
> > http://lkml.kernel.org/r/alpine.LRH.2.21.1802261049140.4893@math.ut.
> > ee --- Hello,
> > 
> > I don't have the full explanation yet but here's a preliminary
> > patch.
> > 
> > Thanks.
> > 
> >  block/blk-timeout.c |    2 +-
> >  1 file changed, 1 insertion(+), 1 deletion(-)
> > 
> > diff --git a/block/blk-timeout.c b/block/blk-timeout.c
> > index a05e367..f0e6e41 100644
> > --- a/block/blk-timeout.c
> > +++ b/block/blk-timeout.c
> > @@ -165,7 +165,7 @@ void blk_abort_request(struct request *req)
> > 
> >  		 * No need for fancy synchronizations.
> >  		 */
> >  		
> >  		blk_rq_set_deadline(req, jiffies);
> > 
> > -		mod_timer(&req->q->timeout, 0);
> > +		kblockd_schedule_work(&req->q->timeout_work);
> > 
> >  	} else {
> >  	
> >  		if (blk_mark_rq_complete(req))
> >  		
> >  			return;


-- 
Martin