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authorWill Deacon <will.deacon@arm.com>2016-09-05 11:56:05 +0100
committerCatalin Marinas <catalin.marinas@arm.com>2016-09-09 12:33:48 +0100
commit872c63fbf9e153146b07f0cece4da0d70b283eeb (patch)
tree86880c47da4f3557f5673fdb1cb3e00a660fff7d
parentc6935931c1894ff857616ff8549b61236a19148f (diff)
downloadlwn-872c63fbf9e153146b07f0cece4da0d70b283eeb.tar.gz
lwn-872c63fbf9e153146b07f0cece4da0d70b283eeb.zip
arm64: spinlocks: implement smp_mb__before_spinlock() as smp_mb()
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: <stable@vger.kernel.org> 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>
-rw-r--r--arch/arm64/include/asm/spinlock.h10
1 files changed, 10 insertions, 0 deletions
diff --git a/arch/arm64/include/asm/spinlock.h b/arch/arm64/include/asm/spinlock.h
index e875a5a551d7..89206b568cd4 100644
--- a/arch/arm64/include/asm/spinlock.h
+++ b/arch/arm64/include/asm/spinlock.h
@@ -363,4 +363,14 @@ 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 */