Merge tag 'drm-misc-fixes-2024-11-28' of https://gitlab.freedesktop.org/drm/misc/kernel into drm-fixes

Short summary of fixes pull:

dma-buf:
- Fix dma_fence_array_signaled() to ensure forward progress

dp_mst:
- Fix MST sideband message body length check

sti:
- Add __iomem for mixer_dbg_mxn()'s parameter

Signed-off-by: Dave Airlie <airlied@redhat.com>

From: Thomas Zimmermann <tzimmermann@suse.de>
Link: https://patchwork.freedesktop.org/patch/msgid/20241128135958.GA244627@linux.fritz.box

1 files changed, 27 insertions, 1 deletions

diff --git a/drivers/dma-buf/dma-fence-array.c b/drivers/dma-buf/dma-fence-array.c
index 8a08ffde31e7..6657d4b30af9 100644
--- a/drivers/dma-buf/dma-fence-array.c
+++ b/drivers/dma-buf/dma-fence-array.c
@@ -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+	 * in the is_signalling_enabled branch might be outdated (num_pending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;
 }