diff options
Diffstat (limited to 'arch/riscv/include/asm/barrier.h')
| -rw-r--r-- | arch/riscv/include/asm/barrier.h | 36 |
1 files changed, 16 insertions, 20 deletions
diff --git a/arch/riscv/include/asm/barrier.h b/arch/riscv/include/asm/barrier.h index 183534b7c39b..c0319cbf1eec 100644 --- a/arch/riscv/include/asm/barrier.h +++ b/arch/riscv/include/asm/barrier.h @@ -39,27 +39,23 @@ #define smp_wmb() RISCV_FENCE(w,w) /* - * These fences exist to enforce ordering around the relaxed AMOs. The - * documentation defines that - * " - * atomic_fetch_add(); - * is equivalent to: - * smp_mb__before_atomic(); - * atomic_fetch_add_relaxed(); - * smp_mb__after_atomic(); - * " - * So we emit full fences on both sides. - */ -#define __smb_mb__before_atomic() smp_mb() -#define __smb_mb__after_atomic() smp_mb() - -/* - * These barriers prevent accesses performed outside a spinlock from being moved - * inside a spinlock. Since RISC-V sets the aq/rl bits on our spinlock only - * enforce release consistency, we need full fences here. + * This is a very specific barrier: it's currently only used in two places in + * the kernel, both in the scheduler. See include/linux/spinlock.h for the two + * orderings it guarantees, but the "critical section is RCsc" guarantee + * mandates a barrier on RISC-V. The sequence looks like: + * + * lr.aq lock + * sc lock <= LOCKED + * smp_mb__after_spinlock() + * // critical section + * lr lock + * sc.rl lock <= UNLOCKED + * + * The AQ/RL pair provides a RCpc critical section, but there's not really any + * way we can take advantage of that here because the ordering is only enforced + * on that one lock. Thus, we're just doing a full fence. */ -#define smb_mb__before_spinlock() smp_mb() -#define smb_mb__after_spinlock() smp_mb() +#define smp_mb__after_spinlock() RISCV_FENCE(rw,rw) #include <asm-generic/barrier.h> |