diff options
| author | Peter Zijlstra <peterz@infradead.org> | 2019-04-24 13:38:23 +0200 |
|---|---|---|
| committer | Greg Kroah-Hartman <gregkh@linuxfoundation.org> | 2019-11-25 15:54:20 +0100 |
| commit | 80989fa23c9f8766bb6c1dad6f673a77f860737a (patch) | |
| tree | 0b72bf8fb84bdce4812a89b6cd1ed030657f389f | |
| parent | d940eddc823283d943eca72dd6672577c6fd2156 (diff) | |
x86/atomic: Fix smp_mb__{before,after}_atomic()
commit 69d927bba39517d0980462efc051875b7f4db185 upstream.
Recent probing at the Linux Kernel Memory Model uncovered a
'surprise'. Strongly ordered architectures where the atomic RmW
primitive implies full memory ordering and
smp_mb__{before,after}_atomic() are a simple barrier() (such as x86)
fail for:
*x = 1;
atomic_inc(u);
smp_mb__after_atomic();
r0 = *y;
Because, while the atomic_inc() implies memory order, it
(surprisingly) does not provide a compiler barrier. This then allows
the compiler to re-order like so:
atomic_inc(u);
*x = 1;
smp_mb__after_atomic();
r0 = *y;
Which the CPU is then allowed to re-order (under TSO rules) like:
atomic_inc(u);
r0 = *y;
*x = 1;
And this very much was not intended. Therefore strengthen the atomic
RmW ops to include a compiler barrier.
NOTE: atomic_{or,and,xor} and the bitops already had the compiler
barrier.
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Signed-off-by: Jari Ruusu <jari.ruusu@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
| -rw-r--r-- | arch/x86/include/asm/atomic.h | 8 | ||||
| -rw-r--r-- | arch/x86/include/asm/atomic64_64.h | 8 | ||||
| -rw-r--r-- | arch/x86/include/asm/barrier.h | 4 |
3 files changed, 10 insertions, 10 deletions
diff --git a/arch/x86/include/asm/atomic.h b/arch/x86/include/asm/atomic.h index 3e8674288198..249fa6b27557 100644 --- a/arch/x86/include/asm/atomic.h +++ b/arch/x86/include/asm/atomic.h @@ -49,7 +49,7 @@ static __always_inline void atomic_add(int i, atomic_t *v) { asm volatile(LOCK_PREFIX "addl %1,%0" : "+m" (v->counter) - : "ir" (i)); + : "ir" (i) : "memory"); } /** @@ -63,7 +63,7 @@ static __always_inline void atomic_sub(int i, atomic_t *v) { asm volatile(LOCK_PREFIX "subl %1,%0" : "+m" (v->counter) - : "ir" (i)); + : "ir" (i) : "memory"); } /** @@ -89,7 +89,7 @@ static __always_inline int atomic_sub_and_test(int i, atomic_t *v) static __always_inline void atomic_inc(atomic_t *v) { asm volatile(LOCK_PREFIX "incl %0" - : "+m" (v->counter)); + : "+m" (v->counter) :: "memory"); } /** @@ -101,7 +101,7 @@ static __always_inline void atomic_inc(atomic_t *v) static __always_inline void atomic_dec(atomic_t *v) { asm volatile(LOCK_PREFIX "decl %0" - : "+m" (v->counter)); + : "+m" (v->counter) :: "memory"); } /** diff --git a/arch/x86/include/asm/atomic64_64.h b/arch/x86/include/asm/atomic64_64.h index 037351022f54..377fa50cc271 100644 --- a/arch/x86/include/asm/atomic64_64.h +++ b/arch/x86/include/asm/atomic64_64.h @@ -44,7 +44,7 @@ static __always_inline void atomic64_add(long i, atomic64_t *v) { asm volatile(LOCK_PREFIX "addq %1,%0" : "=m" (v->counter) - : "er" (i), "m" (v->counter)); + : "er" (i), "m" (v->counter) : "memory"); } /** @@ -58,7 +58,7 @@ static inline void atomic64_sub(long i, atomic64_t *v) { asm volatile(LOCK_PREFIX "subq %1,%0" : "=m" (v->counter) - : "er" (i), "m" (v->counter)); + : "er" (i), "m" (v->counter) : "memory"); } /** @@ -85,7 +85,7 @@ static __always_inline void atomic64_inc(atomic64_t *v) { asm volatile(LOCK_PREFIX "incq %0" : "=m" (v->counter) - : "m" (v->counter)); + : "m" (v->counter) : "memory"); } /** @@ -98,7 +98,7 @@ static __always_inline void atomic64_dec(atomic64_t *v) { asm volatile(LOCK_PREFIX "decq %0" : "=m" (v->counter) - : "m" (v->counter)); + : "m" (v->counter) : "memory"); } /** diff --git a/arch/x86/include/asm/barrier.h b/arch/x86/include/asm/barrier.h index 7f5dcb64cedb..b2a5bef74282 100644 --- a/arch/x86/include/asm/barrier.h +++ b/arch/x86/include/asm/barrier.h @@ -116,7 +116,7 @@ do { \ #endif /* Atomic operations are already serializing on x86 */ -#define smp_mb__before_atomic() barrier() -#define smp_mb__after_atomic() barrier() +#define smp_mb__before_atomic() do { } while (0) +#define smp_mb__after_atomic() do { } while (0) #endif /* _ASM_X86_BARRIER_H */ |