This is a note to let you know that I've just added the patch titled arm64: spinlocks: implement smp_mb__before_spinlock() as smp_mb() to the 4.4-stable tree which can be found at: http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary The filename of the patch is: arm64-spinlocks-implement-smp_mb__before_spinlock-as-smp_mb.patch and it can be found in the queue-4.4 subdirectory. If you, or anyone else, feels it should not be added to the stable tree, please let <stable@xxxxxxxxxxxxxxx> know about it. >From 872c63fbf9e153146b07f0cece4da0d70b283eeb Mon Sep 17 00:00:00 2001 From: Will Deacon <will.deacon@xxxxxxx> Date: Mon, 5 Sep 2016 11:56:05 +0100 Subject: arm64: spinlocks: implement smp_mb__before_spinlock() as smp_mb() From: Will Deacon <will.deacon@xxxxxxx> 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@xxxxxxxxxxxxx> Reported-by: Alan Stern <stern@xxxxxxxxxxxxxxxxxxx> Signed-off-by: Will Deacon <will.deacon@xxxxxxx> Signed-off-by: Catalin Marinas <catalin.marinas@xxxxxxx> Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx> --- arch/arm64/include/asm/spinlock.h | 10 ++++++++++ 1 file changed, 10 insertions(+) --- a/arch/arm64/include/asm/spinlock.h +++ b/arch/arm64/include/asm/spinlock.h @@ -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 */ Patches currently in stable-queue which might be from will.deacon@xxxxxxx are queue-4.4/arm64-spinlocks-implement-smp_mb__before_spinlock-as-smp_mb.patch -- To unsubscribe from this list: send the line "unsubscribe stable" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html