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Date: Thu, 2 May 2013 11:25:12 -0700
Message-ID: <CAMbhsRSdk-z-67BEEd=zbWLR6=WXjpCk1uJky2ZEONS7FLcmGw@mail.gmail.com>
Subject: Re: [RFC PATCH] drivers: power: Add watchdog timer to catch drivers
 which lockup during suspend.
From: Colin Cross <ccross@android.com>
To: Pavel Machek <pavel@ucw.cz>
Cc: Zoran Markovic <zoran.markovic@linaro.org>,
        lkml <linux-kernel@vger.kernel.org>,
        Linux PM list <linux-pm@vger.kernel.org>,
        Benoit Goby <benoit@android.com>,
        Android Kernel Team <kernel-team@android.com>,
        Todd Poynor <toddpoynor@google.com>, San Mehat <san@google.com>,
        John Stultz <john.stultz@linaro.org>,
        "Rafael J. Wysocki" <rjw@sisk.pl>, Len Brown <len.brown@intel.com>,
        Greg Kroah-Hartman <gregkh@linuxfoundation.org>
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On Thu, May 2, 2013 at 5:30 AM, Pavel Machek <pavel@ucw.cz> wrote:
> Hi!
>
>> >> > do BUG which
>> >> >    dumps stack of current task
>> >> >    kills current task
>> >> >
>> >> > Current task may very well be idle task; in such case you kill the
>> >> > machine. Sounds like you should be doing something else, like kill -9
>> >> > instead of BUG()?
>> >>
>> >> Not much else you can do, you are stuck part way into suspend with a
>> >> driver's suspend callback half executed.  All userspace tasks are
>> >> frozen, and the suspend task is blocked indefinitely.
>> >
>> > Yes, there's better option. Attempt killing the [a]suspend task,
>> > instead of killing the current task.
>>
>> That will leave you in a completely undefined state.  If you just kill
>> the task, you are likely to kill the synchronous suspend task, which
>> is the task that would resume your drivers and unfreeze tasks.  That
>> will leave you with no userspace tasks running, and much of your
>> hardware suspended.  How is that a useful result?  If you somehow
>
> So instead you kill random task? (BUG() from timer kills pretty much
> random task, right?)
>
> If you want to do panic(), do panic().

At least on ARM a BUG() in an interrupt or softirq always results in a
panic, but this can be switched to directly call panic.
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