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

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Date:	Fri, 6 Feb 2015 08:25:31 -0800
From:	Linus Torvalds <torvalds@...ux-foundation.org>
To:	Raghavendra K T <raghavendra.kt@...ux.vnet.ibm.com>
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 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).

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?

                            Linus
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