linux-kernel - Re: [PATCH 1/2] asm-generic: rwsem: ensure sem->cnt is only accessed via atomic_long

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Message-ID: <20140228154121.GC29546@mudshark.cambridge.arm.com>
Date:	Fri, 28 Feb 2014 15:41:22 +0000
From:	Will Deacon <will.deacon@....com>
To:	Peter Hurley <peter@...leysoftware.com>
Cc:	Davidlohr Bueso <davidlohr@...com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"rkuo@...eaurora.org" <rkuo@...eaurora.org>,
	"arnd@...db.de" <arnd@...db.de>,
	"paulus@...ba.org" <paulus@...ba.org>
Subject: Re: [PATCH 1/2] asm-generic: rwsem: ensure sem->cnt is only accessed
 via atomic_long_*

On Fri, Feb 28, 2014 at 12:50:06PM +0000, Peter Hurley wrote:
> On 02/28/2014 07:13 AM, Will Deacon wrote:
> > diff --git a/include/asm-generic/rwsem.h b/include/asm-generic/rwsem.h
> > index 603a0a11e592..2b6401f9e428 100644
> > --- a/include/asm-generic/rwsem.h
> > +++ b/include/asm-generic/rwsem.h
> > @@ -40,14 +40,16 @@ static inline void __down_read(struct rw_semaphore *sem)
> >   static inline int __down_read_trylock(struct rw_semaphore *sem)
> >   {
> >          long tmp;
> > +       atomic_long_t *cnt = (atomic_long_t *)&sem->count;
> 
> The shared rwsem failure paths (kernel/locking/rwsem_xadd.c) peek at
> sem->count as long type, so this isn't really necessary.

Yeah, none of this patch is necessary from a technical perspective. I was
just in the area and tried to make the file at least self-consistent wrt the
atomic API. It's a harmless cleanup.

Will
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