From: Peter Zijlstra <peterz@infradead.org>
To: Oleg Nesterov <oleg@redhat.com>
Cc: Kautuk Consul <consul.kautuk@gmail.com>,
Ingo Molnar <mingo@redhat.com>,
Andrew Morton <akpm@linux-foundation.org>,
Michal Hocko <mhocko@suse.cz>,
David Rientjes <rientjes@google.com>,
Ionut Alexa <ionut.m.alexa@gmail.com>,
Guillaume Morin <guillaume@morinfr.org>,
linux-kernel@vger.kernel.org, Kirill Tkhai <tkhai@yandex.ru>
Subject: Re: [PATCH 1/1] do_exit(): Solve possibility of BUG() due to race with try_to_wake_up()
Date: Tue, 2 Sep 2014 19:39:10 +0200 [thread overview]
Message-ID: <20140902173910.GF27892@worktop.ger.corp.intel.com> (raw)
In-Reply-To: <20140902164714.GA17033@redhat.com>
On Tue, Sep 02, 2014 at 06:47:14PM +0200, Oleg Nesterov wrote:
> But since I already wrote v2 yesterday, let me show it anyway. Perhaps
> you will notice something wrong immediately...
>
> So, once again, this patch adds the ugly "goto" into schedule(). OTOH,
> it removes the ugly spin_unlock_wait(pi_lock).
But schedule() is called _far_ more often than exit(). It would be
really good not to have to do that.
> TASK_DEAD can die. The only valid user is schedule_debug(), trivial to
> change. The usage of TASK_DEAD in task_numa_fault() is wrong in any case.
>
> In fact, I think that the next change can change exit_schedule() to use
> PREEMPT_ACTIVE, and then we can simply remove the TASK_DEAD check in
> schedule_debug().
So you worry about concurrent wakeups vs setting TASK_DEAD and thereby
loosing it, right?
Would not something like:
spin_lock_irq(¤t->pi_lock);
__set_current_state(TASK_DEAD);
spin_unlock_irq(¤t->pi_lock);
Not be race free and similarly expensive to the smp_mb() we have there
now?
> - BUG();
> - /* Avoid "noreturn function does return". */
> - for (;;)
> - cpu_relax(); /* For when BUG is null */
> +void exit_schedule(void)
> +{
> + current->state = TASK_DEAD; /* TODO: kill TASK_DEAD altogether */
> + task_rq(current)->prev_dead = true;
> + __schedule();
> + BUG();
you lost that for loop.
next prev parent reply other threads:[~2014-09-02 17:39 UTC|newest]
Thread overview: 25+ messages / expand[flat|nested] mbox.gz Atom feed top
2014-08-25 10:54 [PATCH 1/1] do_exit(): Solve possibility of BUG() due to race with try_to_wake_up() Kautuk Consul
2014-08-25 15:57 ` Oleg Nesterov
2014-08-26 4:45 ` Kautuk Consul
2014-08-26 15:03 ` Oleg Nesterov
2014-09-01 15:39 ` Peter Zijlstra
2014-09-01 17:58 ` Oleg Nesterov
2014-09-01 19:09 ` Peter Zijlstra
2014-09-02 15:52 ` Oleg Nesterov
2014-09-02 16:47 ` Oleg Nesterov
2014-09-02 17:39 ` Peter Zijlstra [this message]
2014-09-03 13:36 ` Oleg Nesterov
2014-09-03 14:44 ` Peter Zijlstra
2014-09-03 15:18 ` Oleg Nesterov
2014-09-04 7:15 ` Peter Zijlstra
2014-09-04 17:03 ` Paul E. McKenney
2014-09-04 5:04 ` Ingo Molnar
2014-09-04 6:32 ` Peter Zijlstra
2014-09-03 16:08 ` task_numa_fault() && TASK_DEAD Oleg Nesterov
2014-09-03 16:33 ` Rik van Riel
2014-09-04 7:11 ` Peter Zijlstra
2014-09-04 10:39 ` Oleg Nesterov
2014-09-04 19:14 ` Hugh Dickins
2014-09-05 11:35 ` Oleg Nesterov
2014-09-03 9:04 ` [PATCH 1/1] do_exit(): Solve possibility of BUG() due to race with try_to_wake_up() Kirill Tkhai
2014-09-03 9:45 ` Peter Zijlstra
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