From d89e588ca4081615216cc25f2489b0281ac0bfe9 Mon Sep 17 00:00:00 2001 From: Peter Zijlstra Date: Mon, 5 Sep 2016 11:37:53 +0200 Subject: locking: Introduce smp_mb__after_spinlock() Since its inception, our understanding of ACQUIRE, esp. as applied to spinlocks, has changed somewhat. Also, I wonder if, with a simple change, we cannot make it provide more. The problem with the comment is that the STORE done by spin_lock isn't itself ordered by the ACQUIRE, and therefore a later LOAD can pass over it and cross with any prior STORE, rendering the default WMB insufficient (pointed out by Alan). Now, this is only really a problem on PowerPC and ARM64, both of which already defined smp_mb__before_spinlock() as a smp_mb(). At the same time, we can get a much stronger construct if we place that same barrier _inside_ the spin_lock(). In that case we upgrade the RCpc spinlock to an RCsc. That would make all schedule() calls fully transitive against one another. Signed-off-by: Peter Zijlstra (Intel) Acked-by: Will Deacon Cc: Alan Stern Cc: Benjamin Herrenschmidt Cc: Linus Torvalds Cc: Michael Ellerman Cc: Nicholas Piggin Cc: Oleg Nesterov Cc: Paul McKenney Cc: Peter Zijlstra Cc: Thomas Gleixner Signed-off-by: Ingo Molnar --- arch/powerpc/include/asm/spinlock.h | 3 +++ 1 file changed, 3 insertions(+) (limited to 'arch/powerpc') diff --git a/arch/powerpc/include/asm/spinlock.h b/arch/powerpc/include/asm/spinlock.h index 8c1b913de6d7..c1b1ec94b06c 100644 --- a/arch/powerpc/include/asm/spinlock.h +++ b/arch/powerpc/include/asm/spinlock.h @@ -342,5 +342,8 @@ static inline void arch_write_unlock(arch_rwlock_t *rw) #define arch_read_relax(lock) __rw_yield(lock) #define arch_write_relax(lock) __rw_yield(lock) +/* See include/linux/spinlock.h */ +#define smp_mb__after_spinlock() smp_mb() + #endif /* __KERNEL__ */ #endif /* __ASM_SPINLOCK_H */ -- cgit v1.2.3