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Date: Tue, 6 Oct 2015 13:16:46 -0700 From: "H. Peter Anvin" <hpa@...or.com> To: Pranith Kumar <bobby.prani@...il.com>, Thomas Gleixner <tglx@...utronix.de>, Ingo Molnar <mingo@...hat.com>, "maintainer:X86 ARCHITECTURE (32-BIT AND 64-BIT)" <x86@...nel.org>, "open list:X86 ARCHITECTURE (32-BIT AND 64-BIT)" <linux-kernel@...r.kernel.org> Subject: Re: [PATCH] x86: cmpxchg_double: Add missing memory clobber On 10/06/2015 11:54 AM, Pranith Kumar wrote: > We are reading from memory locations pointed to by p1 and p2 in the asm > block. Add a memory clobber flag to make gcc aware of this. > > Signed-off-by: Pranith Kumar <bobby.prani@...il.com> > --- > arch/x86/include/asm/cmpxchg.h | 3 ++- > 1 file changed, 2 insertions(+), 1 deletion(-) > > diff --git a/arch/x86/include/asm/cmpxchg.h b/arch/x86/include/asm/cmpxchg.h > index 4a2e5bc..3e83949 100644 > --- a/arch/x86/include/asm/cmpxchg.h > +++ b/arch/x86/include/asm/cmpxchg.h > @@ -214,7 +214,8 @@ extern void __add_wrong_size(void) > : "=a" (__ret), "+d" (__old2), \ > "+m" (*(p1)), "+m" (*(p2)) \ > : "i" (2 * sizeof(long)), "a" (__old1), \ > - "b" (__new1), "c" (__new2)); \ > + "b" (__new1), "c" (__new2) \ > + : "memory"); \ > __ret; \ > }) NAK. We already have the "+m" for exactly this reason; adding an explicit memory clobber should only be used to prevent movement of *other* memory operations around this one (i.e. a barrier). -hpa -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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