Re: [PATCH,v2] sparc32: unbreak arch_write_unlock()

From: David Miller
Date: Mon Aug 15 2011 - 17:38:21 EST

From: Mikael Pettersson <mikpe@xxxxxxxx>
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@xxxxxxxx>

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