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

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Date:	Mon, 21 Mar 2011 16:41:19 -0400 (EDT)
From:	Nicolas Pitre <nicolas.pitre@...aro.org>
To:	Po-Yu Chuang <ratbert.chuang@...il.com>
cc:	Ashwin Chaugule <ashbertslists@...il.com>,
	Russell King - ARM Linux <linux@....linux.org.uk>,
	Po-Yu Chuang <ratbert@...aday-tech.com>, tony@...mide.com,
	lkml <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 Fri, 18 Mar 2011, Po-Yu Chuang wrote:

> On Fri, Mar 18, 2011 at 1:57 AM, Nicolas Pitre <nicolas.pitre@...aro.org> wrote:
> > Nope.  The code being fixed here was suptly broken so it needs fixing.
> > However this code is almost never used, if at all, as it is a fall-back
> > solution for when all the better alternatives are not available for some
> > reasons (and I'm still wondering what those reasons are for Po-Yu Chuang
> > to actually use that code).  In practice this bug should have affected
> > no one.
> 
> We met this problem while porting an v5 SMP processor because kernel
> selects NEEDS_SYSCALL_FOR_CMPXCHG by default if CPU_32v5.
> 
> After we added our own implementation of __kuser_cmpxchg, this code
> is not needed anymore. But since this is actually a bug, it is still a good
> idea to submit a patch. :-)

Yes.  Please send to RMK's patch system with my ACK.


Nicolas