linux-kernel - Re: [PATCH] ARM: SWP emulation: Restore original *data when failed

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Date:	Thu, 15 Oct 2015 16:36:31 +0800
From:	Shengjiu Wang <shengjiu.wang@...escale.com>
To:	Russell King - ARM Linux <linux@....linux.org.uk>
CC:	<nico@...aro.org>, <ard.biesheuvel@...aro.org>,
	<linux-arm-kernel@...ts.infradead.org>,
	<linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] ARM: SWP emulation: Restore original *data when failed

On Thu, Oct 15, 2015 at 09:24:17AM +0100, Russell King - ARM Linux wrote:
> On Wed, Oct 14, 2015 at 10:51:17AM +0800, Shengjiu Wang wrote:
> > __user_swpX_asm maybe failed in first STREX operation, emulate_swpX
> > will try again, but the *data has been changed in first time. which
> > cause the result is wrong. So need to recover the *data when failed.
> > 
> > Signed-off-by: Shengjiu Wang <shengjiu.wang@...escale.com>
> > ---
> >  arch/arm/kernel/swp_emulate.c | 1 +
> >  1 file changed, 1 insertion(+)
> > 
> > diff --git a/arch/arm/kernel/swp_emulate.c b/arch/arm/kernel/swp_emulate.c
> > index 5b26e7e..c61fbf92 100644
> > --- a/arch/arm/kernel/swp_emulate.c
> > +++ b/arch/arm/kernel/swp_emulate.c
> > @@ -41,6 +41,7 @@
> >  	"1:	strex"B"	%0, %2, [%3]\n"			\
> >  	"	cmp		%0, #0\n"			\
> >  	"	movne		%0, %4\n"			\
> > +	"	movne		%1, %2\n"			\
> >  	"2:\n"							\
> >  	"	.section	 .text.fixup,\"ax\"\n"		\
> >  	"	.align		2\n"				\
> 
> I think I'd prefer this to be:
> 
> 	__asm__ __volatile__(					\
> 	"0:	ldrex"B"	%2, [%3]\n"			\
> 	"1:	strex"B"	%0, %1, [%3]\n" 		\
> 	"	cmp		%0, #0\n"			\
> 	"	moveq		%1, %2\n"			\
> 	"	movne		%0, %4\n"			\
> 
> so that we're not loading into %1 (an in-out non-temporary) but rather
> loading it into a temporary - and only overwriting the saved register
> value if the swap succeeds.
> 
> Thanks.

I am ok with your change. Need I send another patch for this change? or will
you send it by yourself?

best regards
wang shengjiu
> 
> -- 
> FTTC broadband for 0.8mile line: currently at 9.6Mbps down 400kbps up
> according to speedtest.net.
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