linux-kernel - Re: [RFC] mlock/stack guard interaction fixup

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Message-ID: <1282460275.11348.865.camel@localhost.localdomain>
Date:	Sun, 22 Aug 2010 07:57:55 +0100
From:	Ian Campbell <ijc@...lion.org.uk>
To:	Linus Torvalds <torvalds@...ux-foundation.org>
Cc:	linux-kernel@...r.kernel.org, stable@...nel.org,
	stable-review@...nel.org, akpm@...ux-foundation.org,
	alan@...rguk.ukuu.org.uk, Greg KH <gregkh@...e.de>,
	Peter Zijlstra <peterz@...radead.org>,
	Jeremy Fitzhardinge <jeremy@...p.org>
Subject: Re: [RFC] mlock/stack guard interaction fixup

On Sat, 2010-08-21 at 08:48 -0700, Linus Torvalds wrote:
> On Sat, Aug 21, 2010 at 4:56 AM, Ian Campbell <ijc@...lion.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?
> 
> 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=1 EF_ALLOW_MALLOC_0=1 LD_PRELOAD=libefence.so.0.0 make

craps out pretty quickly with:

          CC      init/main.o
        
        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

> 
> 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...
> 
> > 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 grows
> > into the heap scenario impossible?
> 
> 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.
> 
> It should be reasonably easy to do the VM_GROWSUP case too, but
> somebody with a PA-RISC would need to do it.
> 
>                          Linus
> 

-- 
Ian Campbell

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

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