4.4-stable review patch. If anyone has any objections, please let me know.
From: Will Deacon <will.dea...@arm.com>
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 <pet...@infradead.org>
Reported-by: Alan Stern <st...@rowland.harvard.edu>
Signed-off-by: Will Deacon <will.dea...@arm.com>
Signed-off-by: Catalin Marinas <catalin.mari...@arm.com>
Signed-off-by: Greg Kroah-Hartman <gre...@linuxfoundation.org>
arch/arm64/include/asm/spinlock.h | 10 ++++++++++
1 file changed, 10 insertions(+)
@@ -312,4 +312,14 @@ static inline int arch_read_trylock(arch
#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 */