From: Ian Campbell <ijc@hellion.org.uk>
To: Linus Torvalds <torvalds@linux-foundation.org>
Cc: linux-kernel@vger.kernel.org, stable@kernel.org, stable-review@kernel.org,
        akpm@linux-foundation.org, alan@lxorguk.ukuu.org.uk,
        Greg KH <gregkh@suse.de>, Peter Zijlstra <peterz@infradead.org>,
        Jeremy Fitzhardinge <jeremy@goop.org>
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Date: Sun, 22 Aug 2010 07:57:55 +0100
Message-ID: <1282460275.11348.865.camel@localhost.localdomain>
Mime-Version: 1.0
Subject: Re: [RFC] mlock/stack guard interaction fixup
Sender: linux-kernel-owner@vger.kernel.org
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On Sat, 2010-08-21 at 08:48 -0700, Linus Torvalds wrote:
> On Sat, Aug 21, 2010 at 4:56 AM, Ian Campbell <ijc@hellion.org.uk> wrote:
> >
> > I don't know that they are particularly good tests for this change but =
I
> > also ran allmodconfig kernel build and ltp on 2.6.35.3+fixes without
> > issue. Are there any good mlock heavy workloads?
>=20
> mlock itself isn't very interesting, I think more interesting is
> testing that the doubly linked list handles all the cases correctly.
> Something that splits mappings, unmaps partial ones etc etc. Running
> something like Electric Fence is probably a good idea.

EF_DISABLE_BANNER=3D1 EF_ALLOW_MALLOC_0=3D1 LD_PRELOAD=3Dlibefence.so.0.0 m=
ake

craps out pretty quickly with:

          CC      init/main.o
       =20
        ElectricFence Exiting: mprotect() failed: Cannot allocate memory
        make[1]: *** [init/main.o] Error 255
        make: *** [init] Error 2

but it does that with 2.6.35.3, 2.6.35.2, 2.6.35.1 and 2.6.35 too so it
doesn't seem to be breakage relating to any of the stack guard stuff

>=20
> The happy news is that we really didn't have lots of assignments to
> vma->vm_next - they were all pretty cleanly separated into just a
> couple of cases. So I'm pretty confident in the patches. But...
>=20
> > Out of interest, why is there no guard page for the VM_GROWSUP stack
> > case? Is it just that the memory layout on PA-RISC makes the stack grow=
s
> > into the heap scenario impossible?
>=20
> No, it's just that I can't find it in myself to care about PA-RISC, so
> I never wrote the code. I don't think anything else has a grows-up
> stack. And even if I were to write the code, I couldn't even test it.
>=20
> It should be reasonably easy to do the VM_GROWSUP case too, but
> somebody with a PA-RISC would need to do it.
>=20
>                          Linus
>=20

--=20
Ian Campbell

Everybody is going somewhere!!  It's probably a garage sale or a
disaster Movie!!

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