linux-kernel - Re: [PATCH,v2] sparc32: unbreak arch_write

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Message-Id: <20110815.143710.1173702549295979935.davem@davemloft.net>
Date:	Mon, 15 Aug 2011 14:37:10 -0700 (PDT)
From:	David Miller <davem@...emloft.net>
To:	mikpe@...uu.se
Cc:	sparclinux@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH,v2] sparc32: unbreak arch_write_unlock()

From: Mikael Pettersson <mikpe@...uu.se>
Date: Mon, 15 Aug 2011 22:11:50 +0200

> The sparc32 version of arch_write_unlock() is just a plain assignment.
> Unfortunately this allows the compiler to schedule side-effects in a
> protected region to occur after the HW-level unlock, which is broken.
> E.g., the following trivial test case gets miscompiled:
> 
> 	#include <linux/spinlock.h>
> 	rwlock_t lock;
> 	int counter;
> 	void foo(void) { write_lock(&lock); ++counter; write_unlock(&lock); }
> 
> Fixed by adding a compiler memory barrier to arch_write_unlock().  The
> sparc64 version combines the barrier and assignment into a single asm(),
> and implements the operation as a static inline, so that's what I did too.
> 
> Compile-tested with sparc32_defconfig + CONFIG_SMP=y.
> 
> Signed-off-by: Mikael Pettersson <mikpe@...uu.se>

Applied.
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