From 8bf018cf9ff8f0190add86eca518431e368194a1 Mon Sep 17 00:00:00 2001
From: Bas Nieuwenhuizen <bas@basnieuwenhuizen.nl>
Date: Wed, 8 Dec 2021 03:39:35 +0100
Subject: drm/syncobj: Deal with signalled fences in drm_syncobj_find_fence.
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Git-commit: b19926d4f3a660a8b76e5d989ffd1168e619a5c4
Patch-mainline: v5.16-rc5
References: jsc#PED-1166 jsc#PED-1168 jsc#PED-1170 jsc#PED-1218 jsc#PED-1220 jsc#PED-1222 jsc#PED-1223 jsc#PED-1225
dma_fence_chain_find_seqno only ever returns the top fence in the
chain or an unsignalled fence. Hence if we request a seqno that
is already signalled it returns a NULL fence. Some callers are
not prepared to handle this, like the syncobj transfer functions
for example.
This behavior is "new" with timeline syncobj and it looks like
not all callers were updated. To fix this behavior make sure
that a successful drm_sync_find_fence always returns a non-NULL
fence.
v2: Move the fix to drm_syncobj_find_fence from the transfer
functions.
Fixes: ea569910cbab ("drm/syncobj: add transition iotcls between binary and timeline v2")
Cc: stable@vger.kernel.org
Signed-off-by: Bas Nieuwenhuizen <bas@basnieuwenhuizen.nl>
Reviewed-by: Christian König <christian.koenig@amd.com>
Acked-by: Lionel Landwerlin <lionel.g.landwerlin@intel.com>
Signed-off-by: Christian König <christian.koenig@amd.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20211208023935.17018-1-bas@basnieuwenhuizen.nl
Acked-by: Patrik Jakobsson <pjakobsson@suse.de>
---
drivers/gpu/drm/drm_syncobj.c | 11 ++++++++++-
1 file changed, 10 insertions(+), 1 deletion(-)
diff --git a/drivers/gpu/drm/drm_syncobj.c b/drivers/gpu/drm/drm_syncobj.c
index c9a9d74f338c..c313a5b4549c 100644
--- a/drivers/gpu/drm/drm_syncobj.c
+++ b/drivers/gpu/drm/drm_syncobj.c
@@ -404,8 +404,17 @@ int drm_syncobj_find_fence(struct drm_file *file_private,
if (*fence) {
ret = dma_fence_chain_find_seqno(fence, point);
- if (!ret)
+ if (!ret) {
+ /* If the requested seqno is already signaled
+ * drm_syncobj_find_fence may return a NULL
+ * fence. To make sure the recipient gets
+ * signalled, use a new fence instead.
+ */
+ if (!*fence)
+ *fence = dma_fence_get_stub();
+
goto out;
+ }
dma_fence_put(*fence);
} else {
ret = -EINVAL;
--
2.38.1