linux-kernel - Re: [PATCH for stable] x86/spinlocks/paravirt: Fix memory corruption on unlock

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Date:	Wed, 25 Feb 2015 11:08:06 +0100
From:	Ingo Molnar <mingo@...nel.org>
To:	Greg KH <gregkh@...uxfoundation.org>
Cc:	Raghavendra K T <raghavendra.kt@...ux.vnet.ibm.com>,
	tglx@...utronix.de, mingo@...hat.com, hpa@...or.com,
	torvalds@...ux-foundation.org, konrad.wilk@...cle.com,
	pbonzini@...hat.com, peterz@...radead.org,
	paulmck@...ux.vnet.ibm.com, waiman.long@...com, davej@...hat.com,
	oleg@...hat.com, x86@...nel.org, jeremy@...p.org,
	paul.gortmaker@...driver.com, ak@...ux.intel.com,
	jasowang@...hat.com, linux-kernel@...r.kernel.org,
	kvm@...r.kernel.org, virtualization@...ts.linux-foundation.org,
	xen-devel@...ts.xenproject.org, riel@...hat.com,
	borntraeger@...ibm.com, akpm@...ux-foundation.org,
	a.ryabinin@...sung.com, sasha.levin@...cle.com, dave@...olabs.net,
	stable@...r.kernel.org
Subject: Re: [PATCH for stable] x86/spinlocks/paravirt: Fix memory corruption
 on unlock


* Greg KH <gregkh@...uxfoundation.org> wrote:

> > >It's:
> > >
> > >  d6abfdb20223 x86/spinlocks/paravirt: Fix memory corruption on unlock
> > 
> > Yes, This is the original patch. Please note I have taken out the
> > READ_ONCE changes from the original patch to avoid build warnings
> > mentioned below.
> > (Those READ_ONCE changes were cosmetic and was not present in the
> > previous versions)
> > 
> > >
> > >You'll also need this fix from Linus to avoid (harmless)
> > >build warnings:
> > >
> > >  dd36929720f4 kernel: make READ_ONCE() valid on const arguments
> > 
> > So this may not be absolutely necessary with the current patch.
> 
> I'd prefer to be as close as possible to the upstream 
> patch.  So if applying both of these patches will work, 
> I'd much rather do that. Changing patches when 
> backporting them to stable for no good reason than to 
> clean things up, just confuses everyone involved.
> 
> Let's keep our messy history :)

By all means!

You'll first need to cherry-pick these commits:

 927609d622a3 kernel: tighten rules for ACCESS ONCE
 c5b19946eb76 kernel: Fix sparse warning for ACCESS_ONCE
 dd36929720f4 kernel: make READ_ONCE() valid on const arguments

That's the minimum set you will need for backporting, due 
to overlapping changes to the ACCESS_ONCE() definition.

and then apply this commit:

 d6abfdb20223 x86/spinlocks/paravirt: Fix memory corruption on unlock

I've double checked that these commits will cherry-pick 
fine on top of v3.19, in that order, and that an x86-64 
defconfig+kvmconfig+PARAVIRT_SPINLOCK=y kernel builds fine 
without warnings.

I've not boot tested the changes, so if anything breaks 
it's all your fault - while if it works just fine then
I'll be glad to take credit for that.

Thanks,

	Ingo
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