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Unverified Commit 42344113 authored by Peter Zijlstra's avatar Peter Zijlstra Committed by Paul Burton
Browse files

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

arch/mips/include/asm/atomic.h

+7 −7
Original line number Diff line number Diff line
@@ -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

+10 −2
Original line number Diff line number Diff line
@@ -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

+25 −17
Original line number Diff line number Diff line
@@ -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

+3 −3
Original line number Diff line number Diff line
@@ -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;					\