Commit 78ac1c35 authored by Christian König's avatar Christian König
Browse files

dma-buf: fix dma_fence_array_signaled v4 



The function silently assumed that signaling was already enabled for the
dma_fence_array. This meant that without enabling signaling first we would
never see forward progress.

Fix that by falling back to testing each individual fence when signaling
isn't enabled yet.

v2: add the comment suggested by Boris why this is done this way
v3: fix the underflow pointed out by Tvrtko
v4: atomic_read_acquire() as suggested by Tvrtko

Signed-off-by: default avatarChristian König <christian.koenig@amd.com>
Reviewed-by: default avatarBoris Brezillon <boris.brezillon@collabora.com>
Tested-by: default avatarChia-I Wu <olvaffe@gmail.com>
Reviewed-by: default avatarTvrtko Ursulin <tvrtko.ursulin@igalia.com>
Closes: https://gitlab.freedesktop.org/mesa/mesa/-/issues/12094
Cc: <stable@vger.kernel.org>
Link: https://patchwork.freedesktop.org/patch/msgid/20241112121925.18464-1-christian.koenig@amd.com
parent fe52c649

drivers/dma-buf/dma-fence-array.c

+27 −1
Original line number Diff line number Diff line
@@ -103,10 +103,36 @@ static bool dma_fence_array_enable_signaling(struct dma_fence *fence) 
static bool dma_fence_array_signaled(struct dma_fence *fence)

{

	struct dma_fence_array *array = to_dma_fence_array(fence);

	int num_pending;

	unsigned int i;



	if (atomic_read(&array->num_pending) > 0)

	/*

	 * We need to read num_pending before checking the enable_signal bit

	 * to avoid racing with the enable_signaling() implementation, which

	 * might decrement the counter, and cause a partial check.

	 * atomic_read_acquire() pairs with atomic_dec_and_test() in

	 * dma_fence_array_enable_signaling()

	 *

	 * The !--num_pending check is here to account for the any_signaled case

	 * if we race with enable_signaling(), that means the !num_pending check

	 * in the is_signalling_enabled branch might be outdated (num_pending

	 * might have been decremented), but that's fine. The user will get the

	 * right value when testing again later.

	 */

	num_pending = atomic_read_acquire(&array->num_pending);

	if (test_bit(DMA_FENCE_FLAG_ENABLE_SIGNAL_BIT, &array->base.flags)) {

		if (num_pending <= 0)

			goto signal;

		return false;

	}



	for (i = 0; i < array->num_fences; ++i) {

		if (dma_fence_is_signaled(array->fences[i]) && !--num_pending)

			goto signal;

	}

	return false;



signal:

	dma_fence_array_clear_pending_error(array);

	return true;

}