linux-kernel - Re: [2.6.33-rc5] Weird deadlock when shutting down

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Message-ID: <2375c9f91002220034m1beec51co7385a1cdbbcce7d2@mail.gmail.com>
Date:	Mon, 22 Feb 2010 16:34:40 +0800
From:	Américo Wang <xiyou.wangcong@...il.com>
To:	Johannes Berg <johannes@...solutions.net>
Cc:	Xiaotian Feng <xtfeng@...il.com>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Benjamin Herrenschmidt <benh@...nel.crashing.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Ingo Molnar <mingo@...e.hu>,
	Peter Zijlstra <peterz@...radead.org>
Subject: Re: [2.6.33-rc5] Weird deadlock when shutting down

On Sun, Feb 21, 2010 at 7:22 PM, Johannes Berg
<johannes@...solutions.net> wrote:
> On Sun, 2010-02-21 at 12:14 +0100, Johannes Berg wrote:
>
>>         printk("got cpu\n");
>>         for_each_online_cpu(i) {
>>                 sm_work = per_cpu_ptr(stop_machine_work, i);
>>                 INIT_WORK(sm_work, stop_cpu);
>>                 queue_work_on(i, stop_machine_wq, sm_work);
>>         }
>>         /* This will release the thread on our CPU. */
>>         put_cpu();
>>         printk("put cpu\n");
>
> As odd as that may be, it hangs in put_cpu() here.
>

Hmm, does adding synchronize_sched() in _cpu_down() help?

Something like this:

diff --git a/kernel/cpu.c b/kernel/cpu.c
index 677f253..681f5c5 100644
--- a/kernel/cpu.c
+++ b/kernel/cpu.c
@@ -228,6 +228,7 @@ static int __ref _cpu_down(unsigned int cpu, int
tasks_frozen)
        cpumask_copy(old_allowed, &current->cpus_allowed);
        set_cpus_allowed_ptr(current, cpu_active_mask);

+       synchronize_sched();
        err = __stop_machine(take_cpu_down, &tcd_param, cpumask_of(cpu));
        if (err) {
                set_cpu_active(cpu, true);
--
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