linux-kernel - Re: [RFC v4] debug: prevent entering debug mode on panic/exception.

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Message-ID: <CA+RfmHZwGh=nbU3A8OEU3b2woUCu9kDeJm-LSz5C25b1Scsd-Q@mail.gmail.com>
Date:	Wed, 7 Jan 2015 09:06:42 +0530
From:	Kiran Raparthy <kiran.kumar@...aro.org>
To:	Andrew Morton <akpm@...ux-foundation.org>
Cc:	Daniel Thompson <daniel.thompson@...aro.org>,
	LKML <linux-kernel@...r.kernel.org>,
	Colin Cross <ccross@...roid.com>,
	Jason Wessel <jason.wessel@...driver.com>,
	kgdb-bugreport@...ts.sourceforge.net,
	Android Kernel Team <kernel-team@...roid.com>,
	John Stultz <john.stultz@...aro.org>,
	Sumit Semwal <sumit.semwal@...aro.org>
Subject: Re: [RFC v4] debug: prevent entering debug mode on panic/exception.

On 7 January 2015 at 02:47, Andrew Morton <akpm@...ux-foundation.org> wrote:
> On Tue, 06 Jan 2015 15:25:51 +0000 Daniel Thompson <daniel.thompson@...aro.org> wrote:
>
>> >> To avoid entering the debugger on panic/exception without any extra
>> >> configuration, panic_timeout is being used which can be set via
>> >> /proc/sys/kernel/panic at run time and CONFIG_PANIC_TIMEOUT sets the default
>> >> value.
>> >>
>> >> ...
>> >>
>> >
>> > hm.  Why overload the meaning of panic_timeout in this fashion?  If
>> > someone is using kgdb and has panic_timeout set, they'll get quiet a
>> > surprise.
>>
>> Will they?
>>
>> Setting panic_timeout means the user explicitly requested that the
>> machine try to perform an unattended reboot after a panic. Wedging in
>> kgdb during panic on such a system absolutely contradicts the user's
>> request to have an automated reboot.
>>
>> In this case it is not overloading the meaning... we are simply altering
>> kgdb to properly honour the existing meaning.
>>
>> Changing the behaviour for exceptions as well as for panics *might*
>> maybe veer into overloading but even there, I think we are simply better
>> reflecting user intent. It is hard to imagine a user that wants
>> automatic-reboot-on-panic being happy for the kernel to get stuck
>> overnight just because of an oops.
>
> OK, when you put it that way...
>
> Kiran, could we please have an updated patch which includes the above
> observations in the changelog and which documents panic_timeout?
Sure,I'll do that.Thanks for your time.
Regards,
Kiran
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