On Wed, Jul 15, 2020 at 11:49:05AM +0100, Chris Wilson wrote:
When waiting with a callback on the stack, we must remove the callback upon wait completion. Since this will be notified by the fence signal callback, the removal often contends with the fence->lock being held by the signaler. We can look at the list entry to see if the callback was already signaled before we take the contended lock.
Signed-off-by: Chris Wilson chris@chris-wilson.co.uk
drivers/dma-buf/dma-fence.c | 3 +++ 1 file changed, 3 insertions(+)
diff --git a/drivers/dma-buf/dma-fence.c b/drivers/dma-buf/dma-fence.c index 8d5bdfce638e..b910d7bc0854 100644 --- a/drivers/dma-buf/dma-fence.c +++ b/drivers/dma-buf/dma-fence.c @@ -420,6 +420,9 @@ dma_fence_remove_callback(struct dma_fence *fence, struct dma_fence_cb *cb) unsigned long flags; bool ret;
- if (list_empty(&cb->node))
I was about to say "but the races" but then noticed that Paul fixed list_empty to use READ_ONCE like 5 years ago :-)
Reviewed-by: Daniel Vetter daniel.vetter@ffwll.ch
return false;spin_lock_irqsave(fence->lock, flags);
ret = !list_empty(&cb->node);
-- 2.20.1
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