linux-kernel - Re: [PATCH] x86 spinlock: Fix memory corruption on completing completions

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Date:	Sun, 08 Feb 2015 23:19:33 +0530
From:	Raghavendra K T <raghavendra.kt@...ux.vnet.ibm.com>
To:	Linus Torvalds <torvalds@...ux-foundation.org>
CC:	Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...hat.com>, Peter Anvin <hpa@...or.com>,
	Peter Zijlstra <peterz@...radead.org>,
	Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>,
	Paolo Bonzini <pbonzini@...hat.com>,
	Paul McKenney <paulmck@...ux.vnet.ibm.com>,
	Waiman Long <waiman.long@...com>,
	Dave Jones <davej@...hat.com>, Oleg Nesterov <oleg@...hat.com>,
	the arch/x86 maintainers <x86@...nel.org>,
	Jeremy Fitzhardinge <jeremy@...p.org>,
	Paul Gortmaker <paul.gortmaker@...driver.com>,
	Andi Kleen <ak@...ux.intel.com>,
	Jason Wang <jasowang@...hat.com>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	KVM list <kvm@...r.kernel.org>,
	virtualization <virtualization@...ts.linux-foundation.org>,
	xen-devel@...ts.xenproject.org, Rik van Riel <riel@...hat.com>,
	Christian Borntraeger <borntraeger@...ibm.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Andrey Ryabinin <a.ryabinin@...sung.com>,
	Sasha Levin <sasha.levin@...cle.com>
Subject: Re: [PATCH] x86 spinlock: Fix memory corruption on completing completions

On 02/06/2015 09:55 PM, Linus Torvalds wrote:
> On Fri, Feb 6, 2015 at 6:49 AM, Raghavendra K T
> <raghavendra.kt@...ux.vnet.ibm.com> wrote:
>> Paravirt spinlock clears slowpath flag after doing unlock.
> [ fix edited out ]
>
> So I'm not going to be applying this for 3.19, because it's much too
> late and the patch is too scary. Plus the bug probably effectively
> never shows up in real life (it is probably easy to trigger the
> speculative *read* but probably never the actual speculative write
> after dropping the lock last).
>

Understood and agreed.

> This will need a lot of testing by the paravirt people - both
> performance and correctness. So *maybe* for 3.20, but maybe for even
> later, and then marked for stable, of course.
>
> Are there any good paravirt stress-tests that people could run for
> extended times?
>

I have been running several benchmarks (kern, sys, hack, ebizzy etc in
in 1x,2x scenarios. I run them for performance test as well.
(In the current patch I did not get kvm hang in normal run, But
overcommit reproduced it).

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