[ARM] barriers: improve xchg, bitops and atomic SMP barriers
Mathieu Desnoyers pointed out that the ARM barriers were lacking: - cmpxchg, xchg and atomic add return need memory barriers on architectures which can reorder the relative order in which memory read/writes can be seen between CPUs, which seems to include recent ARM architectures. Those barriers are currently missing on ARM. - test_and_xxx_bit were missing SMP barriers. So put these barriers in. Provide separate atomic_add/atomic_sub operations which do not require barriers. Reported-Reviewed-and-Acked-by: Mathieu Desnoyers <mathieu.desnoyers@polymtl.ca> Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>
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@ -114,3 +114,16 @@
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.align 3; \
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.long 9999b,9001f; \
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.previous
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/*
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* SMP data memory barrier
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*/
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.macro smp_dmb
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#ifdef CONFIG_SMP
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#if __LINUX_ARM_ARCH__ >= 7
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dmb
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#elif __LINUX_ARM_ARCH__ == 6
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mcr p15, 0, r0, c7, c10, 5 @ dmb
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#endif
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#endif
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.endm
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@ -44,11 +44,29 @@ static inline void atomic_set(atomic_t *v, int i)
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: "cc");
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}
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static inline void atomic_add(int i, atomic_t *v)
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{
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unsigned long tmp;
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int result;
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__asm__ __volatile__("@ atomic_add\n"
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"1: ldrex %0, [%2]\n"
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" add %0, %0, %3\n"
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" strex %1, %0, [%2]\n"
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" teq %1, #0\n"
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" bne 1b"
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: "=&r" (result), "=&r" (tmp)
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: "r" (&v->counter), "Ir" (i)
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: "cc");
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}
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static inline int atomic_add_return(int i, atomic_t *v)
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{
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unsigned long tmp;
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int result;
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smp_mb();
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__asm__ __volatile__("@ atomic_add_return\n"
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"1: ldrex %0, [%2]\n"
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" add %0, %0, %3\n"
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@ -59,14 +77,34 @@ static inline int atomic_add_return(int i, atomic_t *v)
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: "r" (&v->counter), "Ir" (i)
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: "cc");
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smp_mb();
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return result;
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}
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static inline void atomic_sub(int i, atomic_t *v)
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{
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unsigned long tmp;
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int result;
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__asm__ __volatile__("@ atomic_sub\n"
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"1: ldrex %0, [%2]\n"
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" sub %0, %0, %3\n"
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" strex %1, %0, [%2]\n"
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" teq %1, #0\n"
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" bne 1b"
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: "=&r" (result), "=&r" (tmp)
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: "r" (&v->counter), "Ir" (i)
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: "cc");
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}
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static inline int atomic_sub_return(int i, atomic_t *v)
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{
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unsigned long tmp;
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int result;
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smp_mb();
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__asm__ __volatile__("@ atomic_sub_return\n"
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"1: ldrex %0, [%2]\n"
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" sub %0, %0, %3\n"
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@ -77,6 +115,8 @@ static inline int atomic_sub_return(int i, atomic_t *v)
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: "r" (&v->counter), "Ir" (i)
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: "cc");
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smp_mb();
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return result;
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}
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@ -84,6 +124,8 @@ static inline int atomic_cmpxchg(atomic_t *ptr, int old, int new)
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{
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unsigned long oldval, res;
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smp_mb();
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do {
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__asm__ __volatile__("@ atomic_cmpxchg\n"
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"ldrex %1, [%2]\n"
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@ -95,6 +137,8 @@ static inline int atomic_cmpxchg(atomic_t *ptr, int old, int new)
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: "cc");
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} while (res);
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smp_mb();
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return oldval;
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}
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@ -135,6 +179,7 @@ static inline int atomic_add_return(int i, atomic_t *v)
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return val;
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}
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#define atomic_add(i, v) (void) atomic_add_return(i, v)
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static inline int atomic_sub_return(int i, atomic_t *v)
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{
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@ -148,6 +193,7 @@ static inline int atomic_sub_return(int i, atomic_t *v)
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return val;
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}
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#define atomic_sub(i, v) (void) atomic_sub_return(i, v)
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static inline int atomic_cmpxchg(atomic_t *v, int old, int new)
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{
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@ -187,10 +233,8 @@ static inline int atomic_add_unless(atomic_t *v, int a, int u)
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}
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#define atomic_inc_not_zero(v) atomic_add_unless((v), 1, 0)
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#define atomic_add(i, v) (void) atomic_add_return(i, v)
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#define atomic_inc(v) (void) atomic_add_return(1, v)
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#define atomic_sub(i, v) (void) atomic_sub_return(i, v)
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#define atomic_dec(v) (void) atomic_sub_return(1, v)
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#define atomic_inc(v) atomic_add(1, v)
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#define atomic_dec(v) atomic_sub(1, v)
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#define atomic_inc_and_test(v) (atomic_add_return(1, v) == 0)
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#define atomic_dec_and_test(v) (atomic_sub_return(1, v) == 0)
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@ -200,11 +244,10 @@ static inline int atomic_add_unless(atomic_t *v, int a, int u)
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#define atomic_add_negative(i,v) (atomic_add_return(i, v) < 0)
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/* Atomic operations are already serializing on ARM */
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#define smp_mb__before_atomic_dec() barrier()
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#define smp_mb__after_atomic_dec() barrier()
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#define smp_mb__before_atomic_inc() barrier()
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#define smp_mb__after_atomic_inc() barrier()
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#define smp_mb__before_atomic_dec() smp_mb()
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#define smp_mb__after_atomic_dec() smp_mb()
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#define smp_mb__before_atomic_inc() smp_mb()
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#define smp_mb__after_atomic_inc() smp_mb()
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#include <asm-generic/atomic.h>
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#endif
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@ -248,6 +248,8 @@ static inline unsigned long __xchg(unsigned long x, volatile void *ptr, int size
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unsigned int tmp;
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#endif
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smp_mb();
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switch (size) {
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#if __LINUX_ARM_ARCH__ >= 6
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case 1:
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@ -307,6 +309,7 @@ static inline unsigned long __xchg(unsigned long x, volatile void *ptr, int size
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__bad_xchg(ptr, size), ret = 0;
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break;
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}
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smp_mb();
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return ret;
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}
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@ -815,10 +815,7 @@ __kuser_helper_start:
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*/
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__kuser_memory_barrier: @ 0xffff0fa0
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#if __LINUX_ARM_ARCH__ >= 6 && defined(CONFIG_SMP)
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mcr p15, 0, r0, c7, c10, 5 @ dmb
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#endif
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smp_dmb
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usr_ret lr
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.align 5
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@ -18,12 +18,14 @@
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mov r2, #1
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add r1, r1, r0, lsr #3 @ Get byte offset
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mov r3, r2, lsl r3 @ create mask
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smp_dmb
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1: ldrexb r2, [r1]
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ands r0, r2, r3 @ save old value of bit
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\instr r2, r2, r3 @ toggle bit
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strexb ip, r2, [r1]
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cmp ip, #0
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bne 1b
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smp_dmb
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cmp r0, #0
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movne r0, #1
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2: mov pc, lr
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