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

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Message-ID: <2375c9f91002220112q351044a4ycf4ee7dc2630c16d@mail.gmail.com>
Date:	Mon, 22 Feb 2010 17:12:10 +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 Mon, Feb 22, 2010 at 5:04 PM, Johannes Berg
<johannes@...solutions.net> wrote:
> On Mon, 2010-02-22 at 16:34 +0800, Américo Wang wrote:
>> 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?
>
> No luck.
>

Ok, thanks.

Since it hangs in put_cpu() which is just preempt_enable(), so I began
to suspect if we need a synchronize_sched(), or some barrier perhaps.
I am not sure at all.

Before other experts look at this, I think doing a bisect would be very
useful.

Again, thanks for your testing!
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