linux-kernel - Re: [PATCH v2] arm: cmpxchg syscall should data abort if page not write

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Date:	Thu, 17 Mar 2011 13:37:49 -0400
From:	Ashwin Chaugule <ashbertslists@...il.com>
To:	Nicolas Pitre <nicolas.pitre@...aro.org>
Cc:	Po-Yu Chuang <ratbert.chuang@...il.com>, linux@....linux.org.uk,
	Po-Yu Chuang <ratbert@...aday-tech.com>, tony@...mide.com,
	linux-kernel@...r.kernel.org, joe@...ches.com,
	linux-arm-kernel@...ts.infradead.org
Subject: Re: [PATCH v2] arm: cmpxchg syscall should data abort if page not write

On Thu, Mar 17, 2011 at 1:01 PM, Nicolas Pitre <nicolas.pitre@...aro.org> wrote:
> On Tue, 15 Mar 2011, Po-Yu Chuang wrote:
>
>> From: Po-Yu Chuang <ratbert@...aday-tech.com>
>>
>> If the page to cmpxchg is user mode read only (not write),
>> we should simulate a data abort first.
>>
>> Signed-off-by: Po-Yu Chuang <ratbert@...aday-tech.com>
>
> Acked-by: Nicolas Pitre <nicolas.pitre@...aro.org>
>
>> ---
>> v2:
>> remove !pte_young() check
>>
>>  arch/arm/kernel/traps.c |    2 +-
>>  1 files changed, 1 insertions(+), 1 deletions(-)
>>
>> diff --git a/arch/arm/kernel/traps.c b/arch/arm/kernel/traps.c
>> index 446aee9..eac7c05 100644
>> --- a/arch/arm/kernel/traps.c
>> +++ b/arch/arm/kernel/traps.c
>> @@ -563,7 +563,7 @@ asmlinkage int arm_syscall(int no, struct pt_regs *regs)
>>               if (!pmd_present(*pmd))
>>                       goto bad_access;
>>               pte = pte_offset_map_lock(mm, pmd, addr, &ptl);
>> -             if (!pte_present(*pte) || !pte_dirty(*pte)) {
>> +             if (!pte_present(*pte) || !pte_write(*pte) || !pte_dirty(*pte)) {
>>                       pte_unmap_unlock(pte, ptl);
>>                       goto bad_access;
>>               }
>> --
>> 1.6.3.3
>>


Just beginning to understand the subtleties involved, so please
correct me if I'm wrong.
Wont this patch also fix the problem that was brought up with futexes
on ARM SMP ?

http://lists.infradead.org/pipermail/linux-arm-kernel/2010-June/017374.html

Cheers,
Ashwin
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