diff options
| -rw-r--r-- | drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3.c | 31 |
1 files changed, 21 insertions, 10 deletions
diff --git a/drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3.c b/drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3.c index d16d35c78c06..7a6aea3b61c1 100644 --- a/drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3.c +++ b/drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3.c @@ -487,20 +487,26 @@ static void arm_smmu_cmdq_skip_err(struct arm_smmu_device *smmu) */ static void arm_smmu_cmdq_shared_lock(struct arm_smmu_cmdq *cmdq) { - int val; - /* - * We can try to avoid the cmpxchg() loop by simply incrementing the - * lock counter. When held in exclusive state, the lock counter is set - * to INT_MIN so these increments won't hurt as the value will remain - * negative. + * When held in exclusive state, the lock counter is set to INT_MIN + * so these increments won't hurt as the value will remain negative. + * The increment will also signal the exclusive locker that there are + * shared waiters. */ if (atomic_fetch_inc_relaxed(&cmdq->lock) >= 0) return; - do { - val = atomic_cond_read_relaxed(&cmdq->lock, VAL >= 0); - } while (atomic_cmpxchg_relaxed(&cmdq->lock, val, val + 1) != val); + /* + * Someone else is holding the lock in exclusive state, so wait + * for them to finish. Since we already incremented the lock counter, + * no exclusive lock can be acquired until we finish. We don't need + * the return value since we only care that the exclusive lock is + * released (i.e. the lock counter is non-negative). + * Once the exclusive locker releases the lock, the sign bit will + * be cleared and our increment will make the lock counter positive, + * allowing us to proceed. + */ + atomic_cond_read_relaxed(&cmdq->lock, VAL > 0); } static void arm_smmu_cmdq_shared_unlock(struct arm_smmu_cmdq *cmdq) @@ -527,9 +533,14 @@ static bool arm_smmu_cmdq_shared_tryunlock(struct arm_smmu_cmdq *cmdq) __ret; \ }) +/* + * Only clear the sign bit when releasing the exclusive lock this will + * allow any shared_lock() waiters to proceed without the possibility + * of entering the exclusive lock in a tight loop. + */ #define arm_smmu_cmdq_exclusive_unlock_irqrestore(cmdq, flags) \ ({ \ - atomic_set_release(&cmdq->lock, 0); \ + atomic_fetch_andnot_release(INT_MIN, &cmdq->lock); \ local_irq_restore(flags); \ }) |