Re: [Intel-gfx] [PATCH 2/5] dma-fence: Serialise signal enabling (dma_fence_enable_sw_signaling)

On 03/10/2019 22:00, Chris Wilson wrote:

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@chris-wilson.co.uk

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);
• 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;
  

• 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);
  

Tracepoint used to come before the enable_signaling call so probably best to keep it like that.

• }
• 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;

The rest looks correct to me.

Regards,

Tvrtko