linux-kernel - Re: [PATCH] mm: don't overwrite mm->def_flags in do

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Message-ID: <20130207135904.0ca7a3d5@thinkpad>
Date:	Thu, 7 Feb 2013 13:59:04 +0100
From:	Gerald Schaefer <gerald.schaefer@...ibm.com>
To:	Andrew Morton <akpm@...ux-foundation.org>
Cc:	linux-kernel@...r.kernel.org, linux-mm@...ck.org,
	Vivek Goyal <vgoyal@...hat.com>,
	Hugh Dickins <hughd@...gle.com>,
	David Rientjes <rientjes@...gle.com>,
	Mel Gorman <mgorman@...e.de>,
	Martin Schwidefsky <schwidefsky@...ibm.com>,
	Heiko Carstens <heiko.carstens@...ibm.com>,
	Michel Lespinasse <walken@...gle.com>
Subject: Re: [PATCH] mm: don't overwrite mm->def_flags in do_mlockall()

On Wed, 6 Feb 2013 12:51:03 -0800
Andrew Morton <akpm@...ux-foundation.org> wrote:

> On Wed,  6 Feb 2013 16:49:34 +0100
> Gerald Schaefer <gerald.schaefer@...ibm.com> wrote:
> 
> > With commit 8e72033 "thp: make MADV_HUGEPAGE check for
> > mm->def_flags" the VM_NOHUGEPAGE flag may be set on s390 in
> > mm->def_flags for certain processes, to prevent future thp
> > mappings. This would be overwritten by do_mlockall(), which sets it
> > back to 0 with an optional VM_LOCKED flag set.
> > 
> > To fix this, instead of overwriting mm->def_flags in do_mlockall(),
> > only the VM_LOCKED flag should be set or cleared.
> 
> What are the user-visible effects here?  Looking at the 274023da1e8
> changelog, I'm guessing that it might be pretty nasty - kvm breakage?

Yes, though at the moment there should be no mlockall()/munlockall()
involved with kvm/qemu. So currently no user-visible effects, Vivek
found this while reading the do_mlockall() code, but it might be a
good idea to add this to stable.
Could you add a "Cc: stable@...r.kernel.org # v3.7+"?

Thanks,
Gerald

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