[Intel-gfx] [PATCH v3] dma-fence: Serialise signal enabling (dma_fence_enable_sw_signaling)

[Ruhl, Michael J]

>-----Original Message-----
>From: Intel-gfx [mailto:intel-gfx-bounces at lists.freedesktop.org] On Behalf Of
>Chris Wilson
>Sent: Thursday, October 3, 2019 9:24 AM
>To: intel-gfx at lists.freedesktop.org
>Cc: dri-devel at lists.freedesktop.org
>Subject: [Intel-gfx] [PATCH v3] dma-fence: Serialise signal enabling
>(dma_fence_enable_sw_signaling)
>
>Make dma_fence_enable_sw_signaling() behave like its
>dma_fence_add_callback() and dma_fence_default_wait() counterparts and
>perform the test to enable signaling under the fence->lock, along with
>the action to do so. This ensure that should an implementation be trying
>to flush the cb_list (by signaling) on retirement before freeing the
>fence, it can do so in a race-free manner.
>
>See also 0fc89b6802ba ("dma-fence: Simply wrap dma_fence_signal_locked
>with dma_fence_signal").
>
>v2: Refactor all 3 enable_signaling paths to use a common function.
>
>Signed-off-by: Chris Wilson <chris at chris-wilson.co.uk>
>---
>Return false for "could not _enable_ signaling as it was already
>signaled"
>---
> drivers/dma-buf/dma-fence.c | 78 +++++++++++++++++--------------------
> 1 file changed, 35 insertions(+), 43 deletions(-)
>
>diff --git a/drivers/dma-buf/dma-fence.c b/drivers/dma-buf/dma-fence.c
>index 2c136aee3e79..b58528c1cc9d 100644
>--- a/drivers/dma-buf/dma-fence.c
>+++ b/drivers/dma-buf/dma-fence.c
>@@ -273,6 +273,30 @@ void dma_fence_free(struct dma_fence *fence)
> }
> EXPORT_SYMBOL(dma_fence_free);
>
>+static bool __dma_fence_enable_signaling(struct dma_fence *fence)
>+{
>+	bool was_set;
>+
>+	lockdep_assert_held(fence->lock);

With this held...

>+	was_set =
>test_and_set_bit(DMA_FENCE_FLAG_ENABLE_SIGNAL_BIT,
>+				   &fence->flags);
>+
>+	if (test_bit(DMA_FENCE_FLAG_SIGNALED_BIT, &fence->flags))
>+		return false;

Would making these the non-atomic versions be useful (and/or reasonable)?

Mike

>+
>+	if (!was_set && fence->ops->enable_signaling) {
>+		if (!fence->ops->enable_signaling(fence)) {
>+			dma_fence_signal_locked(fence);
>+			return false;
>+		}
>+
>+		trace_dma_fence_enable_signal(fence);
>+	}
>+
>+	return true;
>+}
>+
> /**
>  * dma_fence_enable_sw_signaling - enable signaling on fence
>  * @fence: the fence to enable
>@@ -285,19 +309,12 @@ void dma_fence_enable_sw_signaling(struct
>dma_fence *fence)
> {
> 	unsigned long flags;
>
>-	if (!test_and_set_bit(DMA_FENCE_FLAG_ENABLE_SIGNAL_BIT,
>-			      &fence->flags) &&
>-	    !test_bit(DMA_FENCE_FLAG_SIGNALED_BIT, &fence->flags) &&
>-	    fence->ops->enable_signaling) {
>-		trace_dma_fence_enable_signal(fence);
>-
>-		spin_lock_irqsave(fence->lock, flags);
>-
>-		if (!fence->ops->enable_signaling(fence))
>-			dma_fence_signal_locked(fence);
>+	if (test_bit(DMA_FENCE_FLAG_SIGNALED_BIT, &fence->flags))
>+		return;
>
>-		spin_unlock_irqrestore(fence->lock, flags);
>-	}
>+	spin_lock_irqsave(fence->lock, flags);
>+	__dma_fence_enable_signaling(fence);
>+	spin_unlock_irqrestore(fence->lock, flags);
> }
> EXPORT_SYMBOL(dma_fence_enable_sw_signaling);
>
>@@ -331,7 +348,6 @@ int dma_fence_add_callback(struct dma_fence
>*fence, struct dma_fence_cb *cb,
> {
> 	unsigned long flags;
> 	int ret = 0;
>-	bool was_set;
>
> 	if (WARN_ON(!fence || !func))
> 		return -EINVAL;
>@@ -343,25 +359,14 @@ int dma_fence_add_callback(struct dma_fence
>*fence, struct dma_fence_cb *cb,
>
> 	spin_lock_irqsave(fence->lock, flags);
>
>-	was_set =
>test_and_set_bit(DMA_FENCE_FLAG_ENABLE_SIGNAL_BIT,
>-				   &fence->flags);
>-
>-	if (test_bit(DMA_FENCE_FLAG_SIGNALED_BIT, &fence->flags))
>-		ret = -ENOENT;
>-	else if (!was_set && fence->ops->enable_signaling) {
>-		trace_dma_fence_enable_signal(fence);
>-
>-		if (!fence->ops->enable_signaling(fence)) {
>-			dma_fence_signal_locked(fence);
>-			ret = -ENOENT;
>-		}
>-	}
>-
>-	if (!ret) {
>+	if (__dma_fence_enable_signaling(fence)) {
> 		cb->func = func;
> 		list_add_tail(&cb->node, &fence->cb_list);
>-	} else
>+	} else {
> 		INIT_LIST_HEAD(&cb->node);
>+		ret = -ENOENT;
>+	}
>+
> 	spin_unlock_irqrestore(fence->lock, flags);
>
> 	return ret;
>@@ -461,7 +466,6 @@ dma_fence_default_wait(struct dma_fence *fence,
>bool intr, signed long timeout)
> 	struct default_wait_cb cb;
> 	unsigned long flags;
> 	signed long ret = timeout ? timeout : 1;
>-	bool was_set;
>
> 	if (test_bit(DMA_FENCE_FLAG_SIGNALED_BIT, &fence->flags))
> 		return ret;
>@@ -473,21 +477,9 @@ dma_fence_default_wait(struct dma_fence *fence,
>bool intr, signed long timeout)
> 		goto out;
> 	}
>
>-	was_set =
>test_and_set_bit(DMA_FENCE_FLAG_ENABLE_SIGNAL_BIT,
>-				   &fence->flags);
>-
>-	if (test_bit(DMA_FENCE_FLAG_SIGNALED_BIT, &fence->flags))
>+	if (!__dma_fence_enable_signaling(fence))
> 		goto out;
>
>-	if (!was_set && fence->ops->enable_signaling) {
>-		trace_dma_fence_enable_signal(fence);
>-
>-		if (!fence->ops->enable_signaling(fence)) {
>-			dma_fence_signal_locked(fence);
>-			goto out;
>-		}
>-	}
>-
> 	if (!timeout) {
> 		ret = 0;
> 		goto out;
>--
>2.23.0
>
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