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sparc32: unbreak arch_write_unlock()

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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@it.uu.se>
Signed-off-by: David S. Miller <davem@davemloft.net>
This commit is contained in:
Mikael Pettersson 2011-08-15 10:11:50 +00:00 committed by David S. Miller
parent a0fba3eb05
commit 3f6aa0b113
1 changed files with 9 additions and 2 deletions
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11
arch/sparc/include/asm/spinlock_32.h
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@ -131,6 +131,15 @@ static inline void arch_write_lock(arch_rwlock_t *rw)
*(volatile __u32 *)&lp->lock = ~0U;
}
static void inline arch_write_unlock(arch_rwlock_t *lock)
{
__asm__ __volatile__(
" st %%g0, [%0]"
: /* no outputs */
: "r" (lock)
: "memory");
}
static inline int arch_write_trylock(arch_rwlock_t *rw)
{
unsigned int val;
@ -175,8 +184,6 @@ static inline int __arch_read_trylock(arch_rwlock_t *rw)
res; \
})
#define arch_write_unlock(rw) do { (rw)->lock = 0; } while(0)
#define arch_spin_lock_flags(lock, flags) arch_spin_lock(lock)
#define arch_read_lock_flags(rw, flags) arch_read_lock(rw)
#define arch_write_lock_flags(rw, flags) arch_write_lock(rw)