4.9-stable review patch. If anyone has any objections, please let me know.
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From: Will Deacon will.deacon@arm.com
[ Upstream commit 1cfc63b5ae60fe7e01773f38132f98d8b13a99a0 ]
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 Signed-off-by: Sasha Levin alexander.levin@microsoft.com Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org --- arch/arm64/include/asm/cmpxchg.h | 4 +++- 1 file changed, 3 insertions(+), 1 deletion(-)
--- a/arch/arm64/include/asm/cmpxchg.h +++ b/arch/arm64/include/asm/cmpxchg.h @@ -229,7 +229,9 @@ static inline void __cmpwait_case_##name 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" \