From b19926d4f3a660a8b76e5d989ffd1168e619a5c4 Mon Sep 17 00:00:00 2001

From: Bas Nieuwenhuizen <bas@basnieuwenhuizen.nl>

Date: Wed, 8 Dec 2021 03:39:35 +0100

Subject: [PATCH] drm/syncobj: Deal with signalled fences in drm_syncobj_find_fence.

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Git-commit: b19926d4f3a660a8b76e5d989ffd1168e619a5c4

Patch-mainline: v5.16-rc5

References: git-fixes

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: Takashi Iwai <tiwai@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;

-- 

2.31.1