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Commit 42344113 authored by Peter Zijlstra's avatar Peter Zijlstra Committed by Paul Burton
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mips/atomic: Fix smp_mb__{before,after}_atomic() 

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 MIPS
without WEAK_REORDERING_BEYOND_LLSC) 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.
Reported-by: default avatarAndrea Parri <andrea.parri@amarulasolutions.com>
Signed-off-by: default avatarPeter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: default avatarPaul Burton <paul.burton@mips.com>
parent 1c6c1ca3
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Inline Side-by-side
Showing with 45 additions and 29 deletions
arch/mips/include/asm/atomic.h
View file @ 42344113
......@@ -68,7 +68,7 @@ static __inline__ void atomic_##op(int i, atomic_t * v) \
"\t" __scbeqz " %0, 1b \n" \
" .set pop \n" \
: "=&r" (temp), "+" GCC_OFF_SMALL_ASM() (v->counter) \
: "Ir" (i)); \
: "Ir" (i) : __LLSC_CLOBBER); \
} else { \
unsigned long flags; \
\
......@@ -98,7 +98,7 @@ static __inline__ int atomic_##op##_return_relaxed(int i, atomic_t * v) \
" .set pop \n" \
: "=&r" (result), "=&r" (temp), \
"+" GCC_OFF_SMALL_ASM() (v->counter) \
: "Ir" (i)); \
: "Ir" (i) : __LLSC_CLOBBER); \
} else { \
unsigned long flags; \
\
......@@ -132,7 +132,7 @@ static __inline__ int atomic_fetch_##op##_relaxed(int i, atomic_t * v) \
" move %0, %1 \n" \
: "=&r" (result), "=&r" (temp), \
"+" GCC_OFF_SMALL_ASM() (v->counter) \
: "Ir" (i)); \
: "Ir" (i) : __LLSC_CLOBBER); \
} else { \
unsigned long flags; \
\
......@@ -210,7 +210,7 @@ static __inline__ int atomic_sub_if_positive(int i, atomic_t * v)
" .set pop \n"
: "=&r" (result), "=&r" (temp),
"+" GCC_OFF_SMALL_ASM() (v->counter)
: "Ir" (i));
: "Ir" (i) : __LLSC_CLOBBER);
} else {
unsigned long flags;
......@@ -270,7 +270,7 @@ static __inline__ void atomic64_##op(s64 i, atomic64_t * v) \
"\t" __scbeqz " %0, 1b \n" \
" .set pop \n" \
: "=&r" (temp), "+" GCC_OFF_SMALL_ASM() (v->counter) \
: "Ir" (i)); \
: "Ir" (i) : __LLSC_CLOBBER); \
} else { \
unsigned long flags; \
\
......@@ -300,7 +300,7 @@ static __inline__ s64 atomic64_##op##_return_relaxed(s64 i, atomic64_t * v) \
" .set pop \n" \
: "=&r" (result), "=&r" (temp), \
"+" GCC_OFF_SMALL_ASM() (v->counter) \
: "Ir" (i)); \
: "Ir" (i) : __LLSC_CLOBBER); \
} else { \
unsigned long flags; \
\
......@@ -334,7 +334,7 @@ static __inline__ s64 atomic64_fetch_##op##_relaxed(s64 i, atomic64_t * v) \
" .set pop \n" \
: "=&r" (result), "=&r" (temp), \
"+" GCC_OFF_SMALL_ASM() (v->counter) \
: "Ir" (i)); \
: "Ir" (i) : __LLSC_CLOBBER); \
} else { \
unsigned long flags; \
\
......
arch/mips/include/asm/barrier.h
View file @ 42344113
......@@ -211,14 +211,22 @@
#define __smp_wmb() barrier()
#endif
/*
* When LL/SC does imply order, it must also be a compiler barrier to avoid the
* compiler from reordering where the CPU will not. When it does not imply
* order, the compiler is also free to reorder across the LL/SC loop and
* ordering will be done by smp_llsc_mb() and friends.
*/
#if defined(CONFIG_WEAK_REORDERING_BEYOND_LLSC) && defined(CONFIG_SMP)
#define __WEAK_LLSC_MB " sync \n"
#define smp_llsc_mb() __asm__ __volatile__(__WEAK_LLSC_MB : : :"memory")
#define __LLSC_CLOBBER
#else
#define __WEAK_LLSC_MB " \n"
#define smp_llsc_mb() do { } while (0)
#define __LLSC_CLOBBER "memory"
#endif
#define smp_llsc_mb() __asm__ __volatile__(__WEAK_LLSC_MB : : :"memory")
#ifdef CONFIG_CPU_CAVIUM_OCTEON
#define smp_mb__before_llsc() smp_wmb()
#define __smp_mb__before_llsc() __smp_wmb()
......
arch/mips/include/asm/bitops.h
View file @ 42344113
......@@ -66,7 +66,8 @@ static inline void set_bit(unsigned long nr, volatile unsigned long *addr)
" beqzl %0, 1b \n"
" .set pop \n"
: "=&r" (temp), "=" GCC_OFF_SMALL_ASM() (*m)
: "ir" (1UL << bit), GCC_OFF_SMALL_ASM() (*m));
: "ir" (1UL << bit), GCC_OFF_SMALL_ASM() (*m)
: __LLSC_CLOBBER);
#if defined(CONFIG_CPU_MIPSR2) || defined(CONFIG_CPU_MIPSR6)
} else if (kernel_uses_llsc && __builtin_constant_p(bit)) {
loongson_llsc_mb();
......@@ -76,7 +77,8 @@ static inline void set_bit(unsigned long nr, volatile unsigned long *addr)
" " __INS "%0, %3, %2, 1 \n"
" " __SC "%0, %1 \n"
: "=&r" (temp), "+" GCC_OFF_SMALL_ASM() (*m)
: "ir" (bit), "r" (~0));
: "ir" (bit), "r" (~0)
: __LLSC_CLOBBER);
} while (unlikely(!temp));
#endif /* CONFIG_CPU_MIPSR2 || CONFIG_CPU_MIPSR6 */
} else if (kernel_uses_llsc) {
......@@ -90,7 +92,8 @@ static inline void set_bit(unsigned long nr, volatile unsigned long *addr)
" " __SC "%0, %1 \n"
" .set pop \n"
: "=&r" (temp), "+" GCC_OFF_SMALL_ASM() (*m)
: "ir" (1UL << bit));
: "ir" (1UL << bit)
: __LLSC_CLOBBER);
} while (unlikely(!temp));
} else
__mips_set_bit(nr, addr);
......@@ -122,7 +125,8 @@ static inline void clear_bit(unsigned long nr, volatile unsigned long *addr)
" beqzl %0, 1b \n"
" .set pop \n"
: "=&r" (temp), "+" GCC_OFF_SMALL_ASM() (*m)
: "ir" (~(1UL << bit)));
: "ir" (~(1UL << bit))
: __LLSC_CLOBBER);
#if defined(CONFIG_CPU_MIPSR2) || defined(CONFIG_CPU_MIPSR6)
} else if (kernel_uses_llsc && __builtin_constant_p(bit)) {
loongson_llsc_mb();
......@@ -132,7 +136,8 @@ static inline void clear_bit(unsigned long nr, volatile unsigned long *addr)
" " __INS "%0, $0, %2, 1 \n"
" " __SC "%0, %1 \n"
: "=&r" (temp), "+" GCC_OFF_SMALL_ASM() (*m)
: "ir" (bit));
: "ir" (bit)
: __LLSC_CLOBBER);
} while (unlikely(!temp));
#endif /* CONFIG_CPU_MIPSR2 || CONFIG_CPU_MIPSR6 */
} else if (kernel_uses_llsc) {
......@@ -146,7 +151,8 @@ static inline void clear_bit(unsigned long nr, volatile unsigned long *addr)
" " __SC "%0, %1 \n"
" .set pop \n"
: "=&r" (temp), "+" GCC_OFF_SMALL_ASM() (*m)
: "ir" (~(1UL << bit)));
: "ir" (~(1UL << bit))
: __LLSC_CLOBBER);
} while (unlikely(!temp));
} else
__mips_clear_bit(nr, addr);
......@@ -192,7 +198,8 @@ static inline void change_bit(unsigned long nr, volatile unsigned long *addr)
" beqzl %0, 1b \n"
" .set pop \n"
: "=&r" (temp), "+" GCC_OFF_SMALL_ASM() (*m)
: "ir" (1UL << bit));
: "ir" (1UL << bit)
: __LLSC_CLOBBER);
} else if (kernel_uses_llsc) {
unsigned long *m = ((unsigned long *) addr) + (nr >> SZLONG_LOG);
unsigned long temp;
......@@ -207,7 +214,8 @@ static inline void change_bit(unsigned long nr, volatile unsigned long *addr)
" " __SC "%0, %1 \n"
" .set pop \n"
: "=&r" (temp), "+" GCC_OFF_SMALL_ASM() (*m)
: "ir" (1UL << bit));
: "ir" (1UL << bit)
: __LLSC_CLOBBER);
} while (unlikely(!temp));
} else
__mips_change_bit(nr, addr);
......@@ -244,7 +252,7 @@ static inline int test_and_set_bit(unsigned long nr,
" .set pop \n"
: "=&r" (temp), "+" GCC_OFF_SMALL_ASM() (*m), "=&r" (res)
: "r" (1UL << bit)
: "memory");
: __LLSC_CLOBBER);
} else if (kernel_uses_llsc) {
unsigned long *m = ((unsigned long *) addr) + (nr >> SZLONG_LOG);
unsigned long temp;
......@@ -260,7 +268,7 @@ static inline int test_and_set_bit(unsigned long nr,
" .set pop \n"
: "=&r" (temp), "+" GCC_OFF_SMALL_ASM() (*m), "=&r" (res)
: "r" (1UL << bit)
: "memory");
: __LLSC_CLOBBER);
} while (unlikely(!res));
res = temp & (1UL << bit);
......@@ -301,7 +309,7 @@ static inline int test_and_set_bit_lock(unsigned long nr,
" .set pop \n"
: "=&r" (temp), "+m" (*m), "=&r" (res)
: "r" (1UL << bit)
: "memory");
: __LLSC_CLOBBER);
} else if (kernel_uses_llsc) {
unsigned long *m = ((unsigned long *) addr) + (nr >> SZLONG_LOG);
unsigned long temp;
......@@ -317,7 +325,7 @@ static inline int test_and_set_bit_lock(unsigned long nr,
" .set pop \n"
: "=&r" (temp), "+" GCC_OFF_SMALL_ASM() (*m), "=&r" (res)
: "r" (1UL << bit)
: "memory");
: __LLSC_CLOBBER);
} while (unlikely(!res));
res = temp & (1UL << bit);
......@@ -360,7 +368,7 @@ static inline int test_and_clear_bit(unsigned long nr,
" .set pop \n"
: "=&r" (temp), "+" GCC_OFF_SMALL_ASM() (*m), "=&r" (res)
: "r" (1UL << bit)
: "memory");
: __LLSC_CLOBBER);
#if defined(CONFIG_CPU_MIPSR2) || defined(CONFIG_CPU_MIPSR6)
} else if (kernel_uses_llsc && __builtin_constant_p(nr)) {
unsigned long *m = ((unsigned long *) addr) + (nr >> SZLONG_LOG);
......@@ -375,7 +383,7 @@ static inline int test_and_clear_bit(unsigned long nr,
" " __SC "%0, %1 \n"
: "=&r" (temp), "+" GCC_OFF_SMALL_ASM() (*m), "=&r" (res)
: "ir" (bit)
: "memory");
: __LLSC_CLOBBER);
} while (unlikely(!temp));
#endif
} else if (kernel_uses_llsc) {
......@@ -394,7 +402,7 @@ static inline int test_and_clear_bit(unsigned long nr,
" .set pop \n"
: "=&r" (temp), "+" GCC_OFF_SMALL_ASM() (*m), "=&r" (res)
: "r" (1UL << bit)
: "memory");
: __LLSC_CLOBBER);
} while (unlikely(!res));
res = temp & (1UL << bit);
......@@ -437,7 +445,7 @@ static inline int test_and_change_bit(unsigned long nr,
" .set pop \n"
: "=&r" (temp), "+" GCC_OFF_SMALL_ASM() (*m), "=&r" (res)
: "r" (1UL << bit)
: "memory");
: __LLSC_CLOBBER);
} else if (kernel_uses_llsc) {
unsigned long *m = ((unsigned long *) addr) + (nr >> SZLONG_LOG);
unsigned long temp;
......@@ -453,7 +461,7 @@ static inline int test_and_change_bit(unsigned long nr,
" .set pop \n"
: "=&r" (temp), "+" GCC_OFF_SMALL_ASM() (*m), "=&r" (res)
: "r" (1UL << bit)
: "memory");
: __LLSC_CLOBBER);
} while (unlikely(!res));
res = temp & (1UL << bit);
......
arch/mips/include/asm/cmpxchg.h
View file @ 42344113
......@@ -61,7 +61,7 @@ extern unsigned long __xchg_called_with_bad_pointer(void)
" .set pop \n" \
: "=&r" (__ret), "=" GCC_OFF_SMALL_ASM() (*m) \
: GCC_OFF_SMALL_ASM() (*m), "Jr" (val) \
: "memory"); \
: __LLSC_CLOBBER); \
} else { \
unsigned long __flags; \
\
......@@ -135,7 +135,7 @@ static inline unsigned long __xchg(volatile void *ptr, unsigned long x,
"2: \n" \
: "=&r" (__ret), "=" GCC_OFF_SMALL_ASM() (*m) \
: GCC_OFF_SMALL_ASM() (*m), "Jr" (old), "Jr" (new) \
: "memory"); \
: __LLSC_CLOBBER); \
loongson_llsc_mb(); \
} else { \
unsigned long __flags; \
......
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