linux-kernel - Re: [RFC PATCH] drivers: power: Add watchdog timer to catch drivers which lockup during suspend.

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Date:	Thu, 2 May 2013 11:25:12 -0700
From:	Colin Cross <ccross@...roid.com>
To:	Pavel Machek <pavel@....cz>
Cc:	Zoran Markovic <zoran.markovic@...aro.org>,
	lkml <linux-kernel@...r.kernel.org>,
	Linux PM list <linux-pm@...r.kernel.org>,
	Benoit Goby <benoit@...roid.com>,
	Android Kernel Team <kernel-team@...roid.com>,
	Todd Poynor <toddpoynor@...gle.com>,
	San Mehat <san@...gle.com>,
	John Stultz <john.stultz@...aro.org>,
	"Rafael J. Wysocki" <rjw@...k.pl>, Len Brown <len.brown@...el.com>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Subject: Re: [RFC PATCH] drivers: power: Add watchdog timer to catch drivers
 which lockup during suspend.

On Thu, May 2, 2013 at 5:30 AM, Pavel Machek <pavel@....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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