linux-kernel - Re: [PATCH] arm64: Implement 1-,2- byte smp_load_acquire and smp_store

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Message-ID: <20150420160930.GT5561@linux.vnet.ibm.com>
Date:	Mon, 20 Apr 2015 09:09:30 -0700
From:	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
To:	Will Deacon <will.deacon@....com>
Cc:	Andrey Ryabinin <a.ryabinin@...sung.com>,
	Catalin Marinas <Catalin.Marinas@....com>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Peter Zijlstra <peterz@...radead.org>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] arm64: Implement 1-,2- byte smp_load_acquire and
 smp_store_release

On Mon, Apr 20, 2015 at 04:48:24PM +0100, Will Deacon wrote:
> Hi Andrey,
> 
> On Mon, Apr 20, 2015 at 04:45:53PM +0100, Andrey Ryabinin wrote:
> > commit 47933ad41a86 ("arch: Introduce smp_load_acquire(), smp_store_release()")
> > allowed only 4- and 8-byte smp_load_acquire, smp_store_release.
> > So 1- and 2-byte cases weren't implemented in arm64.
> > Later commit 536fa402221f ("compiler: Allow 1- and 2-byte smp_load_acquire()
> > 				and smp_store_release()")
> > allowed to use 1 and 2 byte smp_load_acquire and smp_store_release
> > by adjusting the definition of __native_word().
> > However, 1-,2- byte cases in arm64 version left unimplemented.
> > 
> > Commit 8053871d0f7f ("smp: Fix smp_call_function_single_async() locking")
> > started to use smp_load_acquire() to load 2-bytes csd->flags.
> > That crashes arm64 kernel during the boot.
> > 
> > Implement 1,2 byte cases in arm64's  smp_load_acquire()
> > and smp_store_release() to fix this.
> > 
> > Signed-off-by: Andrey Ryabinin <a.ryabinin@...sung.com>
> 
> I already have an equivalent patch queued in the arm64/fixes branch[1]. I'll
> send a pull shortly.

Even better!  ;-)

							Thanx, Paul

> Will
> 
> [1]
> https://git.kernel.org/cgit/linux/kernel/git/arm64/linux.git/log/?h=fixes/core
> 
> > ---
> >  arch/arm64/include/asm/barrier.h | 16 ++++++++++++++++
> >  1 file changed, 16 insertions(+)
> > 
> > diff --git a/arch/arm64/include/asm/barrier.h b/arch/arm64/include/asm/barrier.h
> > index a5abb00..71f19c4 100644
> > --- a/arch/arm64/include/asm/barrier.h
> > +++ b/arch/arm64/include/asm/barrier.h
> > @@ -65,6 +65,14 @@ do {									\
> >  do {									\
> >  	compiletime_assert_atomic_type(*p);				\
> >  	switch (sizeof(*p)) {						\
> > +	case 1:								\
> > +		asm volatile ("stlrb %w1, %0"				\
> > +				: "=Q" (*p) : "r" (v) : "memory");	\
> > +		break;							\
> > +	case 2:								\
> > +		asm volatile ("stlrh %w1, %0"				\
> > +				: "=Q" (*p) : "r" (v) : "memory");	\
> > +		break;							\
> >  	case 4:								\
> >  		asm volatile ("stlr %w1, %0"				\
> >  				: "=Q" (*p) : "r" (v) : "memory");	\
> > @@ -81,6 +89,14 @@ do {									\
> >  	typeof(*p) ___p1;						\
> >  	compiletime_assert_atomic_type(*p);				\
> >  	switch (sizeof(*p)) {						\
> > +	case 1:								\
> > +		asm volatile ("ldarb %w0, %1"				\
> > +			: "=r" (___p1) : "Q" (*p) : "memory");		\
> > +		break;							\
> > +	case 2:								\
> > +		asm volatile ("ldarh %w0, %1"				\
> > +			: "=r" (___p1) : "Q" (*p) : "memory");		\
> > +		break;							\
> >  	case 4:								\
> >  		asm volatile ("ldar %w0, %1"				\
> >  			: "=r" (___p1) : "Q" (*p) : "memory");		\
> > -- 
> > 2.3.5
> > 
> 

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