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Subject: Re: [RFC PATCH] set TASK_TRACED before arch_ptrace code to fix a
	race
From: Petr Tesarik <ptesarik@suse.cz>
To: Roland McGrath <roland@redhat.com>
Cc: Luming Yu <luming.yu@gmail.com>, LKML <linux-kernel@vger.kernel.org>,
       linux-ia64@vger.kernel.org
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Organization: SuSE CR
Date: Tue, 27 May 2008 08:25:15 +0200
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On Mon, 2008-05-26 at 23:12 -0700, Roland McGrath wrote:
> >  [<a00000010000a9f0>] skip_rbs_switch+0xe0/0x110
> >                                 sp=e000000141c9fe30 bsp=e000000141c90cf8
> >  [<a000000000010740>] __kernel_syscall_via_break+0x0/0x20
> >                                 sp=e000000141ca0000 bsp=e000000141c90cf8

Indeed, there seems to be a large hole here. So, this is either a bug in
the unwinder, or a bug in the RBS synchronization, which causes
corruption. My test machine currently needs some work to run 2.6.25
again, but I'll try your test case as soon as I re-install it later this
week.

Cheers,
Petr Tesarik

> >  [<a0000001000971c0>] ptrace_stop+0xa0/0x3e0
> >                                 sp=e00000014716fdb0 bsp=e000000147160ca8
> >  [<a000000100097650>] ptrace_notify+0x150/0x1c0
> >                                 sp=e00000014716fdb0 bsp=e000000147160c88
> 
> If this is a backtrace of a single thread on the same kernel stack, it has
> a stack depth of over 84MB.  You still need to follow the path inside
> ia64_ptrace_stop() to see how any of this is possible.
> 
> 
> Thanks,
> Roland