On 07-09-2026 08:41 pm, Christian König wrote:
On 9/7/26 16:42, Khatri, Sunil wrote:
On 07-09-2026 02:23 pm, Christian König wrote:
On 9/7/26 10:47, Yogesh Mohan Marimuthu wrote:
If in userq_signal_ioctl only bo_write_handles is passed and
num_bo_read_handles is zero then if there is contention the code is stuck
in drm_exec_until_all_locked()
This happens because read bo's are handled first and then write bo's in
drm_exec_until_all_locked loop. When there is contention in one of the
write bo, exec->contended bo is set and the loop is retried, but
read bo is zero, still drm_exec_retry_on_contention() macro for read bo
is executed without drm_exec_lock_contended() getting executed.
drm_exec_retry_on_contention will keep going to beginning of the loop
causing infinite loop.
Well that is a really good find but clear NAK to the solution.
This if this causes an infinite loop there is a bug somewhere in the drm_exec
object.
My educated guess is that drm_exec_prepare_array() needs to call
drm_exec_lock_contended() even when num_objects is zero.
drm_exec_prepare_array() returns immediately if no of objects is 0. If its not 0 in
that case order of calls from prepare_array is drm_exec_prepare_obj ->
drm_exec_lock_obj -> drm_exec_lock_contended
So contention is never cleaned.
I can patch this up in drm_exec_prepare_array in case no of objects is 0 call
the drm_exec_lock_contended like below.
if(!num_objects)
returndrm_exec_lock_contended(exec);
That sounds reasonable, yes.
Thanks Christian,
sent the patch for review on [email protected]
[PATCH] drm/drm_exec: remove contention for num_objects is 0
have a look please.
Regards
Sunil khatri
Thanks,
Christian.
Regards
Sunil Khatri
Regards,
Christian.
Fix this by only locking and reserving fence for bo only if there are
bo passed userq_signal_ioctl.
Observed this issue when testing with MR
https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/40808
Signed-off-by: Yogesh Mohan Marimuthu <[email protected]>
---
.../gpu/drm/amd/amdgpu/amdgpu_userq_fence.c | 24 +++++++++++--------
1 file changed, 14 insertions(+), 10 deletions(-)
diff --git a/drivers/gpu/drm/amd/amdgpu/amdgpu_userq_fence.c
b/drivers/gpu/drm/amd/amdgpu/amdgpu_userq_fence.c
index c270635c9..135e77837 100644
--- a/drivers/gpu/drm/amd/amdgpu/amdgpu_userq_fence.c
+++ b/drivers/gpu/drm/amd/amdgpu/amdgpu_userq_fence.c
@@ -572,17 +572,21 @@ int amdgpu_userq_signal_ioctl(struct drm_device *dev,
void *data,
(num_read_bo_handles + num_write_bo_handles));
drm_exec_until_all_locked(&exec) {
- r = drm_exec_prepare_array(&exec, gobj_read,
- num_read_bo_handles, 1);
- drm_exec_retry_on_contention(&exec);
- if (r)
- goto exec_fini;
+ if (num_read_bo_handles) {
+ r = drm_exec_prepare_array(&exec, gobj_read,
+ num_read_bo_handles, 1);
+ drm_exec_retry_on_contention(&exec);
+ if (r)
+ goto exec_fini;
+ }
- r = drm_exec_prepare_array(&exec, gobj_write,
- num_write_bo_handles, 1);
- drm_exec_retry_on_contention(&exec);
- if (r)
- goto exec_fini;
+ if (num_write_bo_handles) {
+ r = drm_exec_prepare_array(&exec, gobj_write,
+ num_write_bo_handles, 1);
+ drm_exec_retry_on_contention(&exec);
+ if (r)
+ goto exec_fini;
+ }
}
/* And publish the new fence in the BOs and syncobj */
