From: Mikulas Patocka Date: Thu, 8 May 2014 19:51:37 +0000 (-0400) Subject: metag: fix memory barriers X-Git-Tag: firefly_0821_release~176^2~3910^2~4 X-Git-Url: http://demsky.eecs.uci.edu/git/?a=commitdiff_plain;h=2425ce84026c385b73ae72039f90d042d49e0394;p=firefly-linux-kernel-4.4.55.git metag: fix memory barriers Volatile access doesn't really imply the compiler barrier. Volatile access is only ordered with respect to other volatile accesses, it isn't ordered with respect to general memory accesses. Gcc may reorder memory accesses around volatile access, as we can see in this simple example (if we compile it with optimization, both increments of *b will be collapsed to just one): void fn(volatile int *a, long *b) { (*b)++; *a = 10; (*b)++; } Consequently, we need the compiler barrier after a write to the volatile variable, to make sure that the compiler doesn't reorder the volatile write with something else. Signed-off-by: Mikulas Patocka Cc: stable@vger.kernel.org Acked-by: Peter Zijlstra Signed-off-by: James Hogan --- diff --git a/arch/metag/include/asm/barrier.h b/arch/metag/include/asm/barrier.h index 5d6b4b407dda..2d6f0de77325 100644 --- a/arch/metag/include/asm/barrier.h +++ b/arch/metag/include/asm/barrier.h @@ -15,6 +15,7 @@ static inline void wr_fence(void) volatile int *flushptr = (volatile int *) LINSYSEVENT_WR_FENCE; barrier(); *flushptr = 0; + barrier(); } #else /* CONFIG_METAG_META21 */ @@ -35,6 +36,7 @@ static inline void wr_fence(void) *flushptr = 0; *flushptr = 0; *flushptr = 0; + barrier(); } #endif /* !CONFIG_METAG_META21 */ @@ -68,6 +70,7 @@ static inline void fence(void) volatile int *flushptr = (volatile int *) LINSYSEVENT_WR_ATOMIC_UNLOCK; barrier(); *flushptr = 0; + barrier(); } #define smp_mb() fence() #define smp_rmb() fence()