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: Mon, 1 Sep 2014 21:09:31 +0200 [thread overview]
Message-ID: <20140901190931.GD5806@worktop.ger.corp.intel.com> (raw)
In-Reply-To: <20140901175851.GA15210@redhat.com>
On Mon, Sep 01, 2014 at 07:58:51PM +0200, Oleg Nesterov wrote:
> However, the very fact that another CPU can look at this task_struct
> means that we still need spin_unlock_wait(). If nothing else to ensure
> that try_to_wake_up()->spin_unlock(pi_lock) won't write into the memory
> we are are going to free.
task_struct is RCU freed, if it still has a 'reference' to the task, it
shouldn't be going 'away', right?
> So I think the comment in do exit should be updated too, and smp_mb()
> should be moved under raw_spin_unlock_wait() but ...
>
> But. If am right, doesn't this mean we that have even more problems with
> postmortem wakeups??? Why ttwu() can't _start_ after spin_unlock_wait ?
ttwu should bail at: if (!(p->state & state)) goto out; That should
never match with TASK_DEAD.
Either that; or I should go sleep already :-) I shifted 7 hours
yesterday, so I'm still somewhat jet-lagged.
next prev parent reply other threads:[~2014-09-01 19:09 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 [this message]
2014-09-02 15:52 ` Oleg Nesterov
2014-09-02 16:47 ` Oleg Nesterov
2014-09-02 17:39 ` Peter Zijlstra
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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