[PATCH 3.10 026/129] arm64: spinlock: retry trylock operation if strex fails on free lock

From: Greg Kroah-Hartman
Date: Mon Jan 06 2014 - 18:32:37 EST

3.10-stable review patch. If anyone has any objections, please let me know.


From: Catalin Marinas <catalin.marinas@xxxxxxx>

commit 4ecf7ccb1973fd826456b6ab1e6dfafe9023c753 upstream.

An exclusive store instruction may fail for reasons other than lock
contention (e.g. a cache eviction during the critical section) so, in
line with other architectures using similar exclusive instructions
(alpha, mips, powerpc), retry the trylock operation if the lock appears
to be free but the strex reported failure.

Signed-off-by: Catalin Marinas <catalin.marinas@xxxxxxx>
Reported-by: Tony Thompson <anthony.thompson@xxxxxxx>
Acked-by: Will Deacon <will.deacon@xxxxxxx>
Cc: Mark Brown <broonie@xxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>

arch/arm64/include/asm/spinlock.h | 3 ++-
1 file changed, 2 insertions(+), 1 deletion(-)

--- a/arch/arm64/include/asm/spinlock.h
+++ b/arch/arm64/include/asm/spinlock.h
@@ -59,9 +59,10 @@ static inline int arch_spin_trylock(arch
unsigned int tmp;

asm volatile(
- " ldaxr %w0, %1\n"
+ "2: ldaxr %w0, %1\n"
" cbnz %w0, 1f\n"
" stxr %w0, %w2, %1\n"
+ " cbnz %w0, 2b\n"
: "=&r" (tmp), "+Q" (lock->lock)
: "r" (1)

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