linux-kernel - In many cases softlockup can not be reported after disabling IRQ for long time

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Date:	Tue, 31 Jan 2012 15:28:09 +0800
From:	TAO HU <tghk48@...orola.com>
To:	linux-kernel@...r.kernel.org
Cc:	Ingo Molnar <mingo@...e.hu>
Subject: In many cases softlockup can not be reported after disabling IRQ for
 long time

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On Wed, Jan 25, 2012 at 4:24 PM, TAO HU <tghk48@...orola.com> wrote:
> Hi, All
>
> While playing kernel 3.0.8 with below test code, it does NOT report
> any softlockup with 60%~70% chances.
> NOTE: the softlockup timeout is set to 10 seconds (i.e.
> watchdog_thresh=5) in my test.
> ... ...
> preempt_disable();
> local_irq_disable();
> for (i = 0; i < 20; i++)
>       mdelay(1000);
> local_irq_enable();
> preempt_enable();
> ... ...
>
> However, if I remove local_irq_disable()/local_irq_enable() it will
> report softlockup with no problem.
> I believe it is due to that after local_irq_enable()
> touch_softlockup_watchdog() is called prior softlockup timer.
>
> touch_softlockup_watchdog() basically resets the lockup detection
> process which implies that the 20-second lockup will be ignored.
> I noticed that touch_softlockup_watchdog() is called in dozens of
> places in kernel.
>
> Is that a design limitation or a bug? Any way to improve the situation?
>
> kernel/debug/debug_core.c:453:  touch_softlockup_watchdog_sync();
> kernel/power/hibernate.c:443:   touch_softlockup_watchdog();
> kernel/panic.c:153:             touch_softlockup_watchdog();
> kernel/time/timekeeping.c:684:  touch_softlockup_watchdog();
> kernel/time/tick-sched.c:149:   touch_softlockup_watchdog();
> kernel/time/tick-sched.c:543:   touch_softlockup_watchdog();
> kernel/time/tick-sched.c:596:           touch_softlockup_watchdog();
> kernel/time/tick-sched.c:756:                   touch_softlockup_watchdog();
> kernel/sched_clock.c:277:       touch_softlockup_watchdog();
>
>
>
> --
> Best Regards
> Hu Tao



-- 
Best Regards
Hu Tao
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