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@xxxxxxxxxxxxxxxxxx> > --- > 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@xxxxxxxx> > + return false; > + > spin_lock_irqsave(fence->lock, flags); > > ret = !list_empty(&cb->node); > -- > 2.20.1 > > _______________________________________________ > Intel-gfx mailing list > Intel-gfx@xxxxxxxxxxxxxxxxxxxxx > https://lists.freedesktop.org/mailman/listinfo/intel-gfx -- Daniel Vetter Software Engineer, Intel Corporation http://blog.ffwll.ch _______________________________________________ dri-devel mailing list dri-devel@xxxxxxxxxxxxxxxxxxxxx https://lists.freedesktop.org/mailman/listinfo/dri-devel
