linux-kernel - Re: [RFC PATCH] set TASK_TRACED before arch

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Date:	Wed, 04 Jun 2008 11:16:12 +0200
From:	Petr Tesarik <ptesarik@...e.cz>
To:	Luming Yu <luming.yu@...il.com>
CC:	Roland McGrath <roland@...hat.com>,
	LKML <linux-kernel@...r.kernel.org>, linux-ia64@...r.kernel.org
Subject: Re: [RFC PATCH] set TASK_TRACED before arch_ptrace code to fix a
 race

Luming Yu wrote:
>> It's definitely a bug in strace. For some reason (I don't care about)
>> the execve() syscall produces an extra notification. However, this
>> notification message is suppressed when SIGTRAP is blocked. This
>> explains why the test case fails only when SIGTRAP is blocked.
> 
> This is exact problem I suspected and I was trying to address in my hack..
> Since there are several processes involved in the pretty complex
> ptrace scenario.,
> I need to capture all processes context with kdump to confirm this is
> exact root-cause
> for the problem. But kdump doesn't work for me..I'm trying to solve it now..
> 
> I'm also in doubt about the semantic correctness of the test case..
> Since SIGTRAP is so necessary to get ptrace work, is it legitimate to
> block it in test case?
> 
> One more thing I need to say is:
> Same strace works for utrace enabled kernel on IA64.. If the bug is in
> strace, how could it happen?

No idea, but send me the strace.log file from running

strace -o strace.log strace -f -o log.txt ./test1

and I may be able to tell.

Petr Tesarik
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