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[ARM] barriers: improve xchg, bitops and atomic SMP barriers

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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>
This commit is contained in:
Russell King 2009-05-25 20:58:00 +01:00 • committed by Russell King
parent 290815710b
commit bac4e960b5
5 changed files with 71 additions and 13 deletions
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3
arch/arm/include/asm/system.h
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@ -248,6 +248,8 @@ static inline unsigned long __xchg(unsigned long x, volatile void *ptr, int size
unsigned int tmp;
#endif
smp_mb();
switch (size) {
#if __LINUX_ARM_ARCH__ >= 6
case 1:
@ -307,6 +309,7 @@ static inline unsigned long __xchg(unsigned long x, volatile void *ptr, int size
__bad_xchg(ptr, size), ret = 0;
break;
}
smp_mb();
return ret;
}