From 2aa6f5b0fd052e363bb9d4b547189f0bf6b3d6d3 Mon Sep 17 00:00:00 2001
From: Erik Kurzinger <ekurzinger@nvidia.com>
Date: Wed, 21 Feb 2024 10:44:28 -0800
Subject: [PATCH] drm/syncobj: handle NULL fence in syncobj_eventfd_entry_func
Git-commit: 2aa6f5b0fd052e363bb9d4b547189f0bf6b3d6d3
Patch-mainline: v6.8-rc6
References: git-fixes
During syncobj_eventfd_entry_func, dma_fence_chain_find_seqno may set
the fence to NULL if the given seqno is signaled and a later seqno has
already been submitted. In that case, the eventfd should be signaled
immediately which currently does not happen.
This is a similar issue to the one addressed by commit b19926d4f3a6
("drm/syncobj: Deal with signalled fences in drm_syncobj_find_fence.").
As a fix, if the return value of dma_fence_chain_find_seqno indicates
success but it sets the fence to NULL, we will assign a stub fence to
ensure the following code still signals the eventfd.
v1 -> v2: assign a stub fence instead of signaling the eventfd
Signed-off-by: Erik Kurzinger <ekurzinger@nvidia.com>
Fixes: c7a472297169 ("drm/syncobj: add IOCTL to register an eventfd")
Signed-off-by: Simon Ser <contact@emersion.fr>
Link: https://patchwork.freedesktop.org/patch/msgid/20240221184527.37667-1-ekurzinger@nvidia.com
Acked-by: Takashi Iwai <tiwai@suse.de>
---
drivers/gpu/drm/drm_syncobj.c | 13 ++++++++++++-
1 file changed, 12 insertions(+), 1 deletion(-)
diff --git a/drivers/gpu/drm/drm_syncobj.c b/drivers/gpu/drm/drm_syncobj.c
index 56b0677acfa3..a6c19de46292 100644
--- a/drivers/gpu/drm/drm_syncobj.c
+++ b/drivers/gpu/drm/drm_syncobj.c
@@ -1418,10 +1418,21 @@ syncobj_eventfd_entry_func(struct drm_syncobj *syncobj,
/* This happens inside the syncobj lock */
fence = dma_fence_get(rcu_dereference_protected(syncobj->fence, 1));
+ if (!fence)
+ return;
+
ret = dma_fence_chain_find_seqno(&fence, entry->point);
- if (ret != 0 || !fence) {
+ if (ret != 0) {
+ /* The given seqno has not been submitted yet. */
dma_fence_put(fence);
return;
+ } else if (!fence) {
+ /* If dma_fence_chain_find_seqno returns 0 but sets the fence
+ * to NULL, it implies that the given seqno is signaled and a
+ * later seqno has already been submitted. Assign a stub fence
+ * so that the eventfd still gets signaled below.
+ */
+ fence = dma_fence_get_stub();
}
list_del_init(&entry->node);
--
2.35.3