Date: Wed, 25 Feb 2015 11:08:06 +0100
From: Ingo Molnar <mingo@kernel.org>
To: Greg KH <gregkh@linuxfoundation.org>
Cc: Raghavendra K T <raghavendra.kt@linux.vnet.ibm.com>, tglx@linutronix.de,
        mingo@redhat.com, hpa@zytor.com, torvalds@linux-foundation.org,
        konrad.wilk@oracle.com, pbonzini@redhat.com, peterz@infradead.org,
        paulmck@linux.vnet.ibm.com, waiman.long@hp.com, davej@redhat.com,
        oleg@redhat.com, x86@kernel.org, jeremy@goop.org,
        paul.gortmaker@windriver.com, ak@linux.intel.com, jasowang@redhat.com,
        linux-kernel@vger.kernel.org, kvm@vger.kernel.org,
        virtualization@lists.linux-foundation.org,
        xen-devel@lists.xenproject.org, riel@redhat.com,
        borntraeger@de.ibm.com, akpm@linux-foundation.org,
        a.ryabinin@samsung.com, sasha.levin@oracle.com, dave@stgolabs.net,
        stable@vger.kernel.org
Subject: Re: [PATCH for stable] x86/spinlocks/paravirt: Fix memory corruption
 on unlock
Message-ID: <20150225100806.GA7134@gmail.com>
References: <1424769899-14158-1-git-send-email-raghavendra.kt@linux.vnet.ibm.com>
 <20150224141731.GA16033@kroah.com>
 <20150224144737.GA26074@gmail.com>
 <54ECC0A1.1080802@linux.vnet.ibm.com>
 <20150224183844.GA8654@kroah.com>
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* Greg KH <gregkh@linuxfoundation.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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