Subject: Re: [2.6.33-rc5] Weird deadlock when shutting down
From: Johannes Berg <johannes@sipsolutions.net>
To: Xiaotian Feng <xtfeng@gmail.com>
Cc: =?ISO-8859-1?Q?Am=E9rico?= Wang <xiyou.wangcong@gmail.com>,
       Linus Torvalds <torvalds@linux-foundation.org>,
       Benjamin Herrenschmidt <benh@kernel.crashing.org>,
       "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
       Ingo Molnar <mingo@elte.hu>, Peter Zijlstra <peterz@infradead.org>
In-Reply-To: <7b6bb4a51002210312o2a1d070aneb54c107aeab6952@mail.gmail.com>
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Date: Sun, 21 Feb 2010 12:14:41 +0100
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On Sun, 2010-02-21 at 19:12 +0800, Xiaotian Feng wrote:
> On Sun, Feb 21, 2010 at 6:55 PM, Xiaotian Feng <xtfeng@gmail.com>
> wrote:
> > On Sun, Feb 21, 2010 at 6:43 PM, Johannes Berg
> > <johannes@sipsolutions.net> wrote:
> >> Incidentally, the machine also freezes hard without any output at
> all if
> >> I "echo 0 > /sys/.../cpu1/online".
> >
> > It might be nothing related with cpufreq. I think there's something
> > wrong during the _cpu_down path.
> > put more debug printks into _cpu_down(), if we can find kernel is
> > stuck in which place in _cpu_down, it would be helpful.
>=20
> and it looks like this breakage is only seen on powerMac G5, so it
> might be arch specific. Maybe some commit in powermac breaks G5's
> cpu_down, just a guess ;-)

Hmm, not sure ... it seems to be in __stop_machine(), in this code:

        printk("got cpu\n");
        for_each_online_cpu(i) {
                sm_work =3D 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");


which is weird... the "got cpu" printk is the last thing I see.

johannes

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