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arm64: cmpwait: Clear event register before arming exclusive monitor

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When waiting for a cacheline to change state in cmpwait, we may immediately
wake-up the first time around the outer loop if the event register was
already set (for example, because of the event stream).

Avoid these spurious wakeups by explicitly clearing the event register
before loading the cacheline and setting the exclusive monitor.

Signed-off-by: Will Deacon <will.deacon@arm.com>
Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>
This commit is contained in:
Will Deacon 2018-04-30 13:56:32 +01:00 committed by Catalin Marinas
parent e75bef2a4f
commit 1cfc63b5ae
1 changed files with 3 additions and 1 deletions
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4
arch/arm64/include/asm/cmpxchg.h
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@ -204,7 +204,9 @@ static inline void __cmpwait_case_##name(volatile void *ptr, \
unsigned long tmp; \
\
asm volatile( \
" ldxr" #sz "\t%" #w "[tmp], %[v]\n" \
" sevl\n" \
" wfe\n" \
" ldxr" #sz "\t%" #w "[tmp], %[v]\n" \
" eor %" #w "[tmp], %" #w "[tmp], %" #w "[val]\n" \
" cbnz %" #w "[tmp], 1f\n" \
" wfe\n" \