linux-kernel - Re: [PATCH v2] execve: must clear current->clear_child

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Date:	Sat, 1 Aug 2009 08:44:38 +0200
From:	Oleg Nesterov <oleg@...hat.com>
To:	Eric Dumazet <eric.dumazet@...il.com>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	linux-kernel@...r.kernel.org, drepper@...hat.com, jens@...one.net,
	mingo@...e.hu, peterz@...radead.org, sonnyrao@...ibm.com,
	stable@...nel.org, tglx@...utronix.de
Subject: Re: [PATCH v2] execve: must clear current->clear_child_tid

On 08/01, Eric Dumazet wrote:
>
> I only wonder about core dumping, since mm_release() is also used by exiting tasks.
>
> Isnt clear_child_tid used by gdb or other debugger ?

Afaics it is not...

At least, I can't see how gdb (or any other user-space app) can figure
out the value of ->clear_child_tid.

Not that this really matters, but please note also that it is possible
that the coredumping task has ->clear_child_tid == NULL anyway, even
without this change. The PF_SIGNALED check in mm_release() is not 100&
reliable.

Suppose a thread T sleeps in do_exit()->ptrace_event(PT_TRACE_EXIT) path.
Another thread starts a coredump and kills T via zap_process(). This wakes
up T, it calls exit_mm()->mm_release() without PF_SIGNALED.

Oleg.

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