Quoting Chris Wilson (2019-10-03 10:36:18)
> 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").
>
> Signed-off-by: Chris Wilson <chris@xxxxxxxxxxxxxxxxxx>
> ---
> drivers/dma-buf/dma-fence.c | 11 +++++------
> 1 file changed, 5 insertions(+), 6 deletions(-)
>
> diff --git a/drivers/dma-buf/dma-fence.c b/drivers/dma-buf/dma-fence.c
> index 2c136aee3e79..587727089134 100644
> --- a/drivers/dma-buf/dma-fence.c
> +++ b/drivers/dma-buf/dma-fence.c
> @@ -285,19 +285,18 @@ void dma_fence_enable_sw_signaling(struct dma_fence *fence)
> {
> unsigned long flags;
>
> + if (test_bit(DMA_FENCE_FLAG_SIGNALED_BIT, &fence->flags))
> + return;
> +
> + spin_lock_irqsave(fence->lock, flags);
> if (!test_and_set_bit(DMA_FENCE_FLAG_ENABLE_SIGNAL_BIT,
> &fence->flags) &&
> - !test_bit(DMA_FENCE_FLAG_SIGNALED_BIT, &fence->flags) &&
Staring at this in discussion with Tvrtko, we can't drop this check
either. After which this looks almost identical with the other
enable_signaling callers.
> 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);
> -
> - spin_unlock_irqrestore(fence->lock, flags);
> }
> + spin_unlock_irqrestore(fence->lock, flags);
> }
> EXPORT_SYMBOL(dma_fence_enable_sw_signaling);
>
> --
> 2.23.0
>
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