Merge tag 'gpio-v4.8-3' of git://git.kernel.org/pub/scm/linux/kernel/git/linusw/linux...

[mirror_ubuntu-bionic-kernel.git] / arch / arm64 / include / asm / spinlock.h

diff --git a/arch/arm64/include/asm/spinlock.h b/arch/arm64/include/asm/spinlock.h
index e875a5a551d7debeab3c34ed2d52e9beae7c8f7d..89206b568cd42365090a8be788da1bbd35466f72 100644 (file)
--- 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 */