Re: [PATCH 5/6] dma-fence: Simply wrap dma_fence_signal_locked with dma_fence_signal

Am 17.08.19 um 16:47 schrieb 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.

Signed-off-by: Chris Wilson chris@chris-wilson.co.uk Cc: Christian König christian.koenig@amd.com Cc: Daniel Vetter daniel.vetter@ffwll.ch

---

drivers/dma-buf/dma-fence.c | 43 +++++++++++-------------------------- 1 file changed, 13 insertions(+), 30 deletions(-)

diff --git a/drivers/dma-buf/dma-fence.c b/drivers/dma-buf/dma-fence.c index ff0cd6eae766..89d96e3e6df6 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 +168,19 @@ 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))

• if (test_bit(DMA_FENCE_FLAG_SIGNALED_BIT, &fence->flags)) return -EINVAL;

Actually I think we can completely drop this extra test. Signaling a fence twice shouldn't be the fast path we should optimize for.

Apart from that it looks good to me, Christian.

• 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);