Am 21.09.2016 um 13:36 schrieb Gustavo Padovan:
From: Gustavo Padovan <gustavo.padovan@xxxxxxxxxxxxxxx>
If the fences in the fence_array signal on the fence_array does not have
signalling enabled num_pending will not be updated accordingly.
So when signaling is disabled check the signal of every fence with
fence_is_signaled() and then compare with num_pending to learn if the
fence_array was signalled or not.
If we want to keep the poll_does_not_wait optimization I think we need
something like this. It keeps the same behaviour if signalling is enabled
but tries to calculated the state otherwise.
Signed-off-by: Gustavo Padovan <gustavo.padovan@xxxxxxxxxxxxxxx>
Reviewed-by: Chris Wilson <chris@xxxxxxxxxxxxxxxxxx>
First of all the patch is horrible wrong because fence_array_signaled()
is called without any locks held. So you can run into a race condition
between checking the fences here and enable signaling.
Additional to that I'm not sure if that is such a good idea or not,
cause fence_array_signaled() should be light weight and without calling
enable_signaling there is not guarantee that fences will ever signal.
Regards,
Christian.
---
drivers/dma-buf/fence-array.c | 19 ++++++++++++++++++-
1 file changed, 18 insertions(+), 1 deletion(-)
diff --git a/drivers/dma-buf/fence-array.c b/drivers/dma-buf/fence-array.c
index f1989fc..1eec271 100644
--- a/drivers/dma-buf/fence-array.c
+++ b/drivers/dma-buf/fence-array.c
@@ -75,8 +75,25 @@ static bool fence_array_enable_signaling(struct fence *fence)
static bool fence_array_signaled(struct fence *fence)
{
struct fence_array *array = to_fence_array(fence);
+ int i, num_pending;
+
+ num_pending = atomic_read(&array->num_pending);
+
+ /*
+ * Before signaling is enabled, num_pending is static (set during array
+ * construction as a count of all fences or set to 1 if signal_on_any
+ * flag is passed. To ensure forward progress, i.e. a while
+ * (!fence_is_signaled()) ; busy-loop eventually proceeds, we need to
+ * check the current status of our fences.
+ */
+ if (!test_bit(FENCE_FLAG_ENABLE_SIGNAL_BIT, &fence->flags)) {
+ for (i = 0 ; i < array->num_fences; ++i) {
+ if (fence_is_signaled(array->fences[i]))
+ num_pending--;
+ }
+ }
- return atomic_read(&array->num_pending) <= 0;
+ return num_pending <= 0;
}
static void fence_array_release(struct fence *fence)
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