linux-kernel - Re: splat in kretprobe in get_task

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Message-ID: <r3nd2eobswp.fsf@perdido.sfo.corp.google.com>
Date:	Wed, 04 Jun 2014 08:23:18 -0700
From:	Peter Moody <pmoody@...gle.com>
To:	Masami Hiramatsu <masami.hiramatsu.pt@...achi.com>
Cc:	ananth@...ibm.com, anil.s.keshavamurthy@...el.com,
	davem@...emloft.net, linux-kernel@...r.kernel.org,
	Kees Cook <keescook@...gle.com>
Subject: Re: splat in kretprobe in get_task_mm(current)

On Wed, Jun 04 2014 at 07:07, Masami Hiramatsu wrote:

>> Thank you for reporting that. I've tried to reproduce it with your code, but
>> not succeeded yet. Could you share us your kernel config too?
>
> Hmm, it seems that on my environment (Fedora20, gcc version 4.8.2 20131212),
> do_execve() in sys_execve has been optimized out (and do_execve_common() is
> also renamed). I'll try to rebuild it. However, since such optimization sometimes
> depends on kernel config, I'd like to do it with your config.
>
> Thank you,

Sure thing, sorry for not attaching it to begin with.

One other thing is that, at least on the systems I've been able to repro on, the more processes, the more likely I was to not emit a splat before just deadlocking the machine. eg. on a 12 core machine, I got the splat with 32 processes and a deadlock with 50. On a 2 core qemu virtual machine I got a deadlock with 32 and a splat with something like 12 or 16.

And FWIW, I'm running ubuntu precise, with gcc version 4.6.3 (Ubuntu/Linaro 4.6.3-1ubuntu5)

Cheers,
peter

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