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Subject: Re: [PATCH] fix send_sigqueue() vs thread exit race
From: Thomas Gleixner <tglx@linutronix.de>
Reply-To: tglx@linutronix.de
To: Oleg Nesterov <oleg@tv-sign.ru>
Cc: Ingo Molnar <mingo@elte.hu>, Roland McGrath <roland@redhat.com>,
       George Anzinger <george@mvista.com>, linux-kernel@vger.kernel.org,
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Date: Tue, 23 Aug 2005 12:42:48 +0200
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On Mon, 2005-08-22 at 20:45 +0400, Oleg Nesterov wrote:
> But I know nothing about kernel/posix-cpu-timers.c, I doubt it will work
> for posix_cpu_timer_del(). I don't have time to study posix-cpu-timers now.
> However, I see that __exit_signal() calls posix_cpu_timers_exit_xxx(), so
> may be it can work?

timer->it.cpu.task is set to NULL by posix_cpu_timers_exit(), so the
code in posix_cpu_timer_del returns before accessing tasklist_lock.


The exit functions do not take any locks, but it is not necessary
there. 

posix_run_cpu_timers(p) is called with p=current() and we have
interrupts disabled, so the timer interrupt can not run on this CPU. The
current exiting process can not run at the same time on a different CPU,
so no race and lockup possible here.

tglx