linux-kernel - [PATCH] drm/syncobj: ensure progress for syncobj queries

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Message-ID: <20241017162054.2701638-1-olvaffe@gmail.com>
Date: Thu, 17 Oct 2024 09:20:53 -0700
From: Chia-I Wu <olvaffe@...il.com>
To: Maarten Lankhorst <maarten.lankhorst@...ux.intel.com>,
	Maxime Ripard <mripard@...nel.org>,
	Thomas Zimmermann <tzimmermann@...e.de>,
	David Airlie <airlied@...il.com>,
	Daniel Vetter <daniel@...ll.ch>,
	dri-devel@...ts.freedesktop.org,
	linux-kernel@...r.kernel.org
Cc: faith.ekstrand@...labora.com,
	boris.brezillon@...labora.com
Subject: [PATCH] drm/syncobj: ensure progress for syncobj queries

Userspace might poll a syncobj with the query ioctl.  Call
dma_fence_enable_sw_signaling to ensure dma_fence_is_signaled returns
true in finite time.

---

panvk hits this issue when timeline semaphore is enabled.  It uses the
transfer ioctl to propagate fences.  dma_fence_unwrap_merge converts the
dma_fence_chain to a dma_fence_array.  dma_fence_array_signaled never
return true unless signaling is enabled.
---
 drivers/gpu/drm/drm_syncobj.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/drivers/gpu/drm/drm_syncobj.c b/drivers/gpu/drm/drm_syncobj.c
index 4fcfc0b9b386c..58c5593c897a2 100644
--- a/drivers/gpu/drm/drm_syncobj.c
+++ b/drivers/gpu/drm/drm_syncobj.c
@@ -1689,6 +1689,9 @@ int drm_syncobj_query_ioctl(struct drm_device *dev, void *data,
 			    DRM_SYNCOBJ_QUERY_FLAGS_LAST_SUBMITTED) {
 				point = fence->seqno;
 			} else {
+				/* ensure forward progress */
+				dma_fence_enable_sw_signaling(fence);
+
 				dma_fence_chain_for_each(iter, fence) {
 					if (iter->context != fence->context) {
 						dma_fence_put(iter);
-- 
2.47.0.rc1.288.g06298d1525-goog