linux-kernel - Re: floppy.c soft lockup

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Date:	Sun, 3 Jun 2007 12:14:17 +0400
From:	Oleg Nesterov <oleg@...sign.ru>
To:	Mark Hounschell <dmarkh@....rr.com>
Cc:	Mark Hounschell <markh@...pro.net>,
	Andrew Morton <akpm@...ux-foundation.org>,
	linux-kernel@...r.kernel.org, Ingo Molnar <mingo@...e.hu>
Subject: Re: floppy.c soft lockup

On 06/02, Mark Hounschell wrote:
>
> Jun  2 16:36:11 harley kernel: ERR!! events/1 flush hang: c201dbc0
> c201dbc0 10012 10012
> Jun  2 16:36:11 harley kernel: CURR: 7974 7974 vrsx 93 26
> Jun  2 16:36:11 harley kernel:     wq_barrier_func+0x0/0x8
> Jun  2 16:36:11 harley kernel:     vmstat_update+0x0/0x24
> Jun  2 16:36:11 harley kernel:     ----
> Jun  2 16:36:11 harley kernel:     cache_reap+0x0/0xf4

As expected.

Note that ->nivcsw/->nvcsw doesn't change. There is no "spare time"
on CPU 1, "vrsx" monopolizes CPU. events/1->cache_reap() was preempted
by vrsx, it had no chance to run since then. Note that jobs == 7974
doesn't change too. I forgot to print cwq->thread->state, but it should
be TASK_RUNNING. It would not be possible to kill vrsx if cache_reap()
stalled.

I don't think this is a kernel problem, vrsx breaks flush_workqueue().
Ingo can answer authoritatively, but I think SCHED_RR/SCHED_FIFO were
not designed to be 100% cpu-bound.

That said, I think it makes sense to get rid of flush_scheduled_work()
in floppy.c.

Thanks!

Oleg.

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