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

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Message-ID: <871u5or7qn.fsf@tw-ebiederman.twitter.com>
Date:	Tue, 20 Aug 2013 03:12:32 -0700
From:	ebiederm@...ssion.com (Eric W. Biederman)
To:	Yoshihiro YUNOMAE <yoshihiro.yunomae.ez@...achi.com>
Cc:	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: [PATCH] [BUGFIX] crash/ioapic: Prevent crash_kexec() from deadlocking of ioapic_lock

Yoshihiro YUNOMAE <yoshihiro.yunomae.ez@...achi.com> writes:

> Hi Ingo,
>
> Thank you for fixing typos!
> OK, I'll fix them and rename to ioapic_zap_locks().
>
> Thank you again!


The better fix for this would be to remove the disable_IO_APIC call from
crash_kexec.

I know last time it was investigated the kernel was very close to
working without needing that, and the code will be much more robust in
the long term if we can avoid disabling them in the crashing kernel.

Yoshihiro is there any chance you can look into removing the
disable_IO_APIC entirely?

The apic disablement and the disable_IO_APIC exists entirely due to
limitations in the kernel boot path.

Eric
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