linux-kernel - Re: [V9fs-developer] Hang triggered by udev coldplug, looks like a race

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Message-ID: <20151207224643.GA10531@nautica>
Date:	Mon, 7 Dec 2015 23:46:43 +0100
From:	Dominique Martinet <dominique.martinet@....fr>
To:	Andy Lutomirski <luto@...capital.net>
Cc:	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	V9FS Developers <v9fs-developer@...ts.sourceforge.net>,
	Linux FS Devel <linux-fsdevel@...r.kernel.org>
Subject: Re: [V9fs-developer] Hang triggered by udev coldplug, looks like a
 race

Andy Lutomirski wrote on Mon, Dec 07, 2015:
> On Thu, Dec 3, 2015 at 9:52 PM, Andy Lutomirski <luto@...capital.net> wrote:
> > Sometimes udevadm trigger --action=add hangs the system, and the splat
> > below happens.  This seems to be timing dependent, and I haven't been
> > able to trigger it yet with lockdep enabled, sadly.
> >
> > Any ideas?  I not, I'll try to instrument it better tomorrow.
> 
> More details: this is caused by a storm of /sbin/hotplug UMH calls
> (yes, misconfigured kernel, but still).  /sbin is a symlink to
> /usr/sbin, /usr/sbin/hotplug doesn't exist, and all of the above is on
> rootfs, which is 9p over virtio.
> 
> Pointing uevent_helper at /usr/sbin/hotplug (which still doesn't
> exist) seems to work around it.

Can you reproduce it on a booted system with something like
`seq 1 1000000 | xargs -P 1024 -I{} cat /sbin/foo >&/dev/null` ?

(trying execs might be closer to your workload, not sure how much this
or using umh might change)


Also, what qemu version please just to try to match your environment ?

-- 
Dominique Martinet
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