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

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Date:	Thu, 22 Aug 2013 09:11:37 -0400
From:	Don Zickus <dzickus@...hat.com>
To:	Yoshihiro YUNOMAE <yoshihiro.yunomae.ez@...achi.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: [PATCH] [BUGFIX] crash/ioapic: Prevent crash_kexec() from
 deadlocking of ioapic_lock

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).

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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