| From | Jiri Slaby <> | Subject | [PATCH 3.12 089/119] arm64: spinlocks: implement smp_mb__before_spinlock() as smp_mb() | Date | Thu, 29 Sep 2016 12:25:25 +0200 |
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From: Will Deacon <will.deacon@arm.com>
3.12-stable review patch. If anyone has any objections, please let me know.
===============
commit 872c63fbf9e153146b07f0cece4da0d70b283eeb upstream.
smp_mb__before_spinlock() is intended to upgrade a spin_lock() operation to a full barrier, such that prior stores are ordered with respect to loads and stores occuring inside the critical section.
Unfortunately, the core code defines the barrier as smp_wmb(), which is insufficient to provide the required ordering guarantees when used in conjunction with our load-acquire-based spinlock implementation.
This patch overrides the arm64 definition of smp_mb__before_spinlock() to map to a full smp_mb().
Cc: Peter Zijlstra <peterz@infradead.org> Reported-by: Alan Stern <stern@rowland.harvard.edu> Signed-off-by: Will Deacon <will.deacon@arm.com> Signed-off-by: Catalin Marinas <catalin.marinas@arm.com> Signed-off-by: Jiri Slaby <jslaby@suse.cz> --- arch/arm64/include/asm/spinlock.h | 10 ++++++++++ 1 file changed, 10 insertions(+)
diff --git a/arch/arm64/include/asm/spinlock.h b/arch/arm64/include/asm/spinlock.h index 0defa0728a9b..c3cab6f87de4 100644 --- a/arch/arm64/include/asm/spinlock.h +++ b/arch/arm64/include/asm/spinlock.h @@ -200,4 +200,14 @@ static inline int arch_read_trylock(arch_rwlock_t *rw) #define arch_read_relax(lock) cpu_relax() #define arch_write_relax(lock) cpu_relax() +/* + * Accesses appearing in program order before a spin_lock() operation + * can be reordered with accesses inside the critical section, by virtue + * of arch_spin_lock being constructed using acquire semantics. + * + * In cases where this is problematic (e.g. try_to_wake_up), an + * smp_mb__before_spinlock() can restore the required ordering. + */ +#define smp_mb__before_spinlock() smp_mb() + #endif /* __ASM_SPINLOCK_H */ -- 2.10.0
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