This is a note to let you know that I've just added the patch titled drm/syncobj: Deal with signalled fences in drm_syncobj_find_fence. to the 5.15-stable tree which can be found at: http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary The filename of the patch is: drm-syncobj-deal-with-signalled-fences-in-drm_syncobj_find_fence.patch and it can be found in the queue-5.15 subdirectory. If you, or anyone else, feels it should not be added to the stable tree, please let <stable@xxxxxxxxxxxxxxx> know about it. >From b19926d4f3a660a8b76e5d989ffd1168e619a5c4 Mon Sep 17 00:00:00 2001 From: Bas Nieuwenhuizen <bas@xxxxxxxxxxxxxxxxxxx> Date: Wed, 8 Dec 2021 03:39:35 +0100 Subject: drm/syncobj: Deal with signalled fences in drm_syncobj_find_fence. MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit From: Bas Nieuwenhuizen <bas@xxxxxxxxxxxxxxxxxxx> commit b19926d4f3a660a8b76e5d989ffd1168e619a5c4 upstream. 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@xxxxxxxxxxxxxxx Signed-off-by: Bas Nieuwenhuizen <bas@xxxxxxxxxxxxxxxxxxx> Reviewed-by: Christian König <christian.koenig@xxxxxxx> Acked-by: Lionel Landwerlin <lionel.g.landwerlin@xxxxxxxxx> Signed-off-by: Christian König <christian.koenig@xxxxxxx> Link: https://patchwork.freedesktop.org/patch/msgid/20211208023935.17018-1-bas@xxxxxxxxxxxxxxxxxxx Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx> --- drivers/gpu/drm/drm_syncobj.c | 11 ++++++++++- 1 file changed, 10 insertions(+), 1 deletion(-) --- 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_fi 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; Patches currently in stable-queue which might be from bas@xxxxxxxxxxxxxxxxxxx are queue-5.15/drm-syncobj-deal-with-signalled-fences-in-drm_syncobj_find_fence.patch