[PATCH v3] dma-fence: Simply wrap dma_fence_signal_locked with dma_fence_signal

[Chris Wilson]

Currently dma_fence_signal() tries to avoid the spinlock and only takes
it if absolutely required to walk the callback list. However, to allow
for some users to surreptitiously insert lazy signal callbacks that
do not depend on enabling the signaling mechanism around every fence,
we always need to notify the callbacks on signaling. As such, we will
always need to take the spinlock and dma_fence_signal() effectively
becomes a clone of dma_fence_signal_locked().

v2: Update the test_and_set_bit() before entering the spinlock.
v3: Drop the test_[and_set]_bit() before the spinlock, it's a caller
error so expected to be very unlikely.

Signed-off-by: Chris Wilson <chris at chris-wilson.co.uk>
Cc: Christian König <christian.koenig at amd.com>
Cc: Daniel Vetter <daniel.vetter at ffwll.ch>
---
 drivers/dma-buf/dma-fence.c | 44 ++++++++++---------------------------
 1 file changed, 12 insertions(+), 32 deletions(-)

diff --git a/drivers/dma-buf/dma-fence.c b/drivers/dma-buf/dma-fence.c
index ff0cd6eae766..8a6d0250285d 100644
--- a/drivers/dma-buf/dma-fence.c
+++ b/drivers/dma-buf/dma-fence.c
@@ -129,25 +129,16 @@ EXPORT_SYMBOL(dma_fence_context_alloc);
 int dma_fence_signal_locked(struct dma_fence *fence)
 {
 	struct dma_fence_cb *cur, *tmp;
-	int ret = 0;
 
 	lockdep_assert_held(fence->lock);
 
-	if (WARN_ON(!fence))
+	if (unlikely(test_and_set_bit(DMA_FENCE_FLAG_SIGNALED_BIT,
+				      &fence->flags)))
 		return -EINVAL;
 
-	if (test_and_set_bit(DMA_FENCE_FLAG_SIGNALED_BIT, &fence->flags)) {
-		ret = -EINVAL;
-
-		/*
-		 * we might have raced with the unlocked dma_fence_signal,
-		 * still run through all callbacks
-		 */
-	} else {
-		fence->timestamp = ktime_get();
-		set_bit(DMA_FENCE_FLAG_TIMESTAMP_BIT, &fence->flags);
-		trace_dma_fence_signaled(fence);
-	}
+	fence->timestamp = ktime_get();
+	set_bit(DMA_FENCE_FLAG_TIMESTAMP_BIT, &fence->flags);
+	trace_dma_fence_signaled(fence);
 
 	if (!list_empty(&fence->cb_list)) {
 		list_for_each_entry_safe(cur, tmp, &fence->cb_list, node) {
@@ -156,7 +147,8 @@ int dma_fence_signal_locked(struct dma_fence *fence)
 		}
 		INIT_LIST_HEAD(&fence->cb_list);
 	}
-	return ret;
+
+	return 0;
 }
 EXPORT_SYMBOL(dma_fence_signal_locked);
 
@@ -176,28 +168,16 @@ EXPORT_SYMBOL(dma_fence_signal_locked);
 int dma_fence_signal(struct dma_fence *fence)
 {
 	unsigned long flags;
+	int ret;
 
 	if (!fence)
 		return -EINVAL;
 
-	if (test_and_set_bit(DMA_FENCE_FLAG_SIGNALED_BIT, &fence->flags))
-		return -EINVAL;
-
-	fence->timestamp = ktime_get();
-	set_bit(DMA_FENCE_FLAG_TIMESTAMP_BIT, &fence->flags);
-	trace_dma_fence_signaled(fence);
-
-	if (test_bit(DMA_FENCE_FLAG_ENABLE_SIGNAL_BIT, &fence->flags)) {
-		struct dma_fence_cb *cur, *tmp;
+	spin_lock_irqsave(fence->lock, flags);
+	ret = dma_fence_signal_locked(fence);
+	spin_unlock_irqrestore(fence->lock, flags);
 
-		spin_lock_irqsave(fence->lock, flags);
-		list_for_each_entry_safe(cur, tmp, &fence->cb_list, node) {
-			list_del_init(&cur->node);
-			cur->func(fence, cur);
-		}
-		spin_unlock_irqrestore(fence->lock, flags);
-	}
-	return 0;
+	return ret;
 }
 EXPORT_SYMBOL(dma_fence_signal);
 
-- 
2.23.0.rc1