linux-kernel - Re: Re: Re: [PATCH] [BUGFIX] crash/ioapic: Prevent crash_kexec() from deadlocking of ioapic

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Date:	Tue, 27 Aug 2013 12:41:51 +0900
From:	Yoshihiro YUNOMAE <yoshihiro.yunomae.ez@...achi.com>
To:	Don Zickus <dzickus@...hat.com>
Cc:	"Eric W. Biederman" <ebiederm@...ssion.com>,
	Ingo Molnar <mingo@...nel.org>, linux-kernel@...r.kernel.org,
	Andi Kleen <ak@...ux.intel.com>,
	"H. Peter Anvin" <hpa@...or.com>, Gleb Natapov <gleb@...hat.com>,
	Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>,
	Joerg Roedel <joro@...tes.org>, x86@...nel.org,
	stable@...r.kernel.org, Marcelo Tosatti <mtosatti@...hat.com>,
	Hidehiro Kawai <hidehiro.kawai.ez@...achi.com>,
	Sebastian Andrzej Siewior <sebastian@...akpoint.cc>,
	Ingo Molnar <mingo@...hat.com>,
	Zhang Yanfei <zhangyanfei@...fujitsu.com>,
	yrl.pp-manager.tt@...achi.com,
	Masami Hiramatsu <masami.hiramatsu.pt@...achi.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Seiji Aguchi <seiji.aguchi@....com>,
	Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: Re: Re: [PATCH] [BUGFIX] crash/ioapic: Prevent crash_kexec()
 from deadlocking of ioapic_lock

Hi Don,

Sorry for the late reply.

(2013/08/22 22:11), Don Zickus wrote:
> On Thu, Aug 22, 2013 at 05:38:07PM +0900, Yoshihiro YUNOMAE wrote:
>>> So, I agree with Eric, let's remove the disable_IO_APIC() stuff and keep
>>> the code simpler.
>>
>> Thank you for commenting about my patch.
>> I didn't know you already have submitted the patches for this deadlock
>> problem.
>>
>> I can't answer definitively right now that no problems are induced by
>> removing disable_IO_APIC(). However, my patch should be work well (and
>> has already been merged to -tip tree). So how about taking my patch at
>> first, and then discussing the removal of disabled_IO_APIC()?
>
> It doesn't matter to me.  My orignal patch last year was similar to yours
> until it was suggested that we were working around a problem which was we
> shouldn't touch the IO_APIC code on panic.  Then I wrote the removal of
> disable_IO_APIC patch and did lots of testing on it.  I don't think I have
> seen any issues with it (just the removal of disabling the lapic stuff).

Yes, you really did a lot of testing about this problem according to
your patch(https://lkml.org/lkml/2012/1/31/391). Although you
said jiffies calibration code does not need the PIT in
http://lists.infradead.org/pipermail/kexec/2012-February/006017.html,
I don't understand yet why we can remove disable_IO_APIC.
Would you please explain about the calibration codes?

By the way, can we remove disable_IO_APIC even if an old dump capture
kernel is used?

Thanks,
Yoshihiro YUNOMAE

> Regardless, your patch fixes a similar problem we saw on RHEL, so I am
> happy either way.  The removal of the disable_IO_APIC() just makes the
> code look cleaner.
>
> Cheers,
> Don
> --
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-- 
Yoshihiro YUNOMAE
Software Platform Research Dept. Linux Technology Center
Hitachi, Ltd., Yokohama Research Laboratory
E-mail: yoshihiro.yunomae.ez@...achi.com


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