Messages in this thread Patch in this message | | | Date | Mon, 15 Aug 2011 13:09:09 +0200 | From | Mikael Pettersson <> | Subject | [PATCH,SPARC] make sparc32 arch_write_unlock() match the sparc64 version |
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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(), so that's what I did here as well.
Compiled-tested with a sparc32 SMP kernel.
Signed-off-by: Mikael Pettersson <mikpe@it.uu.se> --- --- linux-3.1-rc2/arch/sparc/include/asm/spinlock_32.h.~1~ 2011-07-22 12:01:08.000000000 +0200 +++ linux-3.1-rc2/arch/sparc/include/asm/spinlock_32.h 2011-08-15 11:43:49.000000000 +0200 @@ -131,6 +131,15 @@ static inline void arch_write_lock(arch_ *(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; @@ -175,7 +184,7 @@ static inline int __arch_read_trylock(ar res; \ }) -#define arch_write_unlock(rw) do { (rw)->lock = 0; } while(0) +#define arch_write_unlock(rw) arch_write_unlock(rw) #define arch_spin_lock_flags(lock, flags) arch_spin_lock(lock) #define arch_read_lock_flags(rw, flags) arch_read_lock(rw)
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