From: Tejun Heo <tj@kernel.org>
To: Hillf Danton <dhillf@gmail.com>
Cc: Rusty Russell <rusty@rustcorp.com.au>,
Andrew Morton <akpm@linux-foundation.org>,
Ingo Molnar <mingo@elte.hu>, LKML <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH 2/2] stop_machine: dequeue work before signal completion
Date: Sat, 9 Feb 2013 11:17:37 -0800 [thread overview]
Message-ID: <20130209191737.GD2875@htj.dyndns.org> (raw)
In-Reply-To: <CAJd=RBBvE-5f1UyJGu32EHGVCXe6rVYY0010SKa56j7OvtPG7g@mail.gmail.com>
Hello, again.
On Fri, Feb 08, 2013 at 11:42:43AM +0800, Hillf Danton wrote:
> As checked with BUG_ON in the case of CPU_UP_PREPARE, we have to dequeue
> work first for further actions, then stopper reaches sane and clear state.
When a CPU is finally put down in either CPU_UP_CANCELLED or
CPU_POST_DEAD, cpu_stop_cpu_callback() signals immediate completion on
all cpu_stop_works still queued on the dead CPU; unfortunately, this
code is buggy in that it doesn't remove the canceled work items off
the stopper->works leaving it corrupted, which will trigger BUG_ON()
during CPU_UP_PREPARE if the CPU is brought back online.
This bug isn't easily triggered because CPU_DOWN has to race against
cpu_stop calls and most, if not all, cpu stop users pin target CPUs.
Fix it by popping each work item off stopper->works.
> Signed-off-by: Hillf Danton <dhillf@gmail.com>
Maybe
Cc: stable@vger.kernel.org
> --- a/kernel/stop_machine.c Fri Feb 8 11:22:44 2013
> +++ b/kernel/stop_machine.c Fri Feb 8 11:29:40 2013
> @@ -342,8 +342,12 @@ static int __cpuinit cpu_stop_cpu_callba
> kthread_stop(stopper->thread);
> /* drain remaining works */
> spin_lock_irq(&stopper->lock);
> - list_for_each_entry(work, &stopper->works, list)
> + while (!list_empty(&stopper->works)) {
> + work = list_first_entry(&stopper->works,
> + struct cpu_stop_work, list);
> + list_del_init(&work->list);
> cpu_stop_signal_done(work->done, false);
> + }
I think your previous version was better with @work declaration moved
inside the while() loop.
Thanks.
--
tejun
next prev parent reply other threads:[~2013-02-09 19:17 UTC|newest]
Thread overview: 6+ messages / expand[flat|nested] mbox.gz Atom feed top
2013-02-08 3:42 [PATCH 2/2] stop_machine: dequeue work before signal completion Hillf Danton
2013-02-08 8:22 ` Namhyung Kim
2013-02-08 12:03 ` Hillf Danton
2013-02-09 19:17 ` Tejun Heo [this message]
2013-02-10 5:26 Hillf Danton
2013-02-12 17:38 ` Tejun Heo
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