linux-kernel - Re: [PROBLEM] hard-lock with kmemtrace, relayfs, and splice

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Date:	Fri, 10 Oct 2008 14:51:44 +0300
From:	Eduard - Gabriel Munteanu <eduard.munteanu@...ux360.ro>
To:	Pekka Enberg <penberg@...helsinki.fi>
Cc:	zanussi@...cast.net, jens.axboe@...cle.com,
	linux-kernel@...r.kernel.org
Subject: Re: [PROBLEM] hard-lock with kmemtrace, relayfs, and splice

On Fri, Oct 10, 2008 at 12:42:03PM +0300, Pekka Enberg wrote:
> (I'm cc'ing Tom, Jens, and LKML.)
> 
> On Fri, 2008-10-10 at 12:10 +0300, Pekka Enberg wrote:
> > > I'm seeing a hard lock on my machine when I run kmemtraced with the
> > > following patch applied:
> > > 
> > > http://git.kernel.org/?p=linux/kernel/git/penberg/slab-2.6.git;a=commitdiff;h=17ca1d5506b1db433f0b7167a627bfd55d319dd3
> > > 
> > > I can enable/disable kmemtrace via the debugfs files fine and can also
> > > read the relay files with cat.
> > > 
> > > Any idea where this is coming from?
> > 
> > OK, it's the first splice() call in reader_thread() that causes the
> > hang. Hmm.
> 
> To recap, with a CONFIG_KMEMTRACE enabled kernel from the
> "topic/kmemtrace" branch of:
> 
>   git://git.kernel.org/pub/scm/linux/kernel/git/penberg/slab-2.6.git topic/kmemtrace
> 
> running the "kmemtraced" program from
> 
>   git://git.kernel.org/pub/scm/linux/kernel/git/penberg/kmemtrace-user.git
> 
> results to a hard lock on my machine. I am unable to find anything
> obviously wrong with it and as I can read/write the relay files just
> fine, I'm beginning to think it's problem in relayfs splice
> implementation.
> 
> Tom, thoughts?
> 
> 		Pekka
>

Hmm, I've seen kmemtraced not stopping, but no hard locks. It seems not
even SIGKILL can stop it. As far as I know, SIGKILL should stop even a
blocking splice() (in case this is the problem). This is what I did:
# ./kmemtraced &
# killall -KILL kmemtraced
... kmemtraced still running and using CPU.


	Eduard

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