Quoting Chris Wilson (2019-10-03 14:19:46)
> 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@xxxxxxxxxxxxxxxxxx>
> ---
> 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..4a1442a93f04 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 true;
Perhaps this should be false for "could not _enable_ signaling as it was
already signaled", which is closer to the original.
> +
> + if (!was_set && fence->ops->enable_signaling) {
> + if (!fence->ops->enable_signaling(fence)) {
> + dma_fence_signal_locked(fence);
> + return true;
> + }
> +
> + trace_dma_fence_enable_signal(fence);
> + }
> +
> + return false;
> +}
> +
> /**
> * 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))
> + if (__dma_fence_enable_signaling(fence)) {
> + INIT_LIST_HEAD(&cb->node);
> 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) {
> + } else {
> cb->func = func;
> list_add_tail(&cb->node, &fence->cb_list);
> - } else
> - INIT_LIST_HEAD(&cb->node);
> + }
> +
> 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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