linux-kernel - Re: please fix FUSION (Was:[v3.13][v3.14][Regression]kthread:makekthread

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Date:	Sun, 23 Mar 2014 07:29:10 -0700
From:	James Bottomley <James.Bottomley@...senPartnership.com>
To:	Thomas Gleixner <tglx@...utronix.de>
Cc:	Tetsuo Handa <penguin-kernel@...ove.SAKURA.ne.jp>, oleg@...hat.com,
	joseph.salisbury@...onical.com, Nagalakshmi.Nandigama@....com,
	Sreekanth.Reddy@....com, rientjes@...gle.com,
	akpm@...ux-foundation.org, torvalds@...ux-foundation.org,
	tj@...nel.org, linux-kernel@...r.kernel.org,
	kernel-team@...ts.ubuntu.com, linux-scsi@...r.kernel.org,
	thenzl@...hat.com
Subject: Re: please fix FUSION
 (Was:[v3.13][v3.14][Regression]kthread:makekthread_create()killable)

On Sun, 2014-03-23 at 15:28 +0100, Thomas Gleixner wrote:
> On Sun, 23 Mar 2014, James Bottomley wrote:
> > On Sun, 2014-03-23 at 09:04 +0100, Thomas Gleixner wrote:
> > > On Sun, 23 Mar 2014, Tetsuo Handa wrote:
> > > 
> > > > Thomas Gleixner wrote:
> > > > > But then systemd/udev mutters:
> > > > > 
> > > > >    "You migh be able to work around the timeout with udev rules and
> > > > >     OPTIONS+="event_timeout=120", but that code was maybe never used
> > > > >     or tested, so it might not work correctly." [1]
> > > > > 
> > > > > AFAICT from the ubuntu bug system [2] nobody bothered even to try that.
> > > > > 
> > > > > And if the udev/systemd event_timeout option is broken it's way better
> > > > > to fix that one instead of hacking random heuristics into the kernel.
> > > > 
> > > > I haven't tried the event_timeout= option but I think it will not work.
> > > > The timeout is hard coded as shown below and there will be no chance for taking
> > > > the event_timeout= option into account.
> > > > 
> > > > ---------- systemd-204/src/udev/udevd.c start ----------
> > > > (...snipped...)
> > > >                         /* check for hanging events */
> > > >                         udev_list_node_foreach(loop, &worker_list) {
> > > >                                 struct worker *worker = node_to_worker(loop);
> > > > 
> > > >                                 if (worker->state != WORKER_RUNNING)
> > > >                                         continue;
> > > > 
> > > >                                 if ((now(CLOCK_MONOTONIC) - worker->event_start_usec) > 30 * 1000 * 1000) {
> > > 
> > > And because systemd has an immutable hardcoded random timeout we add
> > > another hardcoded random timeout into kthread_create() to work around
> > > that.
> > > 
> > > How broken is that?
> > > 
> > > And it seems other people have solved it:
> > > 
> > >     http://www.redhat.com/archives/lvm-devel/2013-September/msg00036.html
> > 
> > I agree with Thomas.  A hardcoded timeout is a systemd bug.  However,
> > could I get confirmation, while you can use this bug to do it, that the
> > patch back in this thread actually fixes the crash when scsi_alloc_host
> > fails, that's the serious SCSI bug, in my view?
> 
> Which patch, the one to kthread_create() or the one to SCSI?

The one to SCSI ... I'm only really interested in the oops when
scsi_host_alloc fails.

James



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