Re: [PATCH] drm/sched: Fix a race in DRM_GPU_SCHED_STAT_NO_HANG test

[Maíra Canal]

Hi Tvrtko,

On 16/07/25 05:48, Tvrtko Ursulin wrote:
The "skip reset" test waits for the timeout handler to run for the
duration of 2 * MOCK_TIMEOUT, and because the mock scheduler opted to

Would it make any sense to wait for 1.5 * MOCK_TIMEOUT? This way we
would guarantee that only one timeout happened. I'm fine with the
current solution as well.

remove the "skip reset" flag once it fires, this gives opportunity for the
timeout handler to run twice. Second time the job will be removed from the
mock scheduler job list and the drm_mock_sched_advance() call in the test
will fail.

Fix it by making the "don't reset" flag persist for the lifetime of the
job and add a new flag to verify that the code path had executed as
expected.

Signed-off-by: Tvrtko Ursulin <tvrtko.ursu...@igalia.com>
Fixes: 1472e7549f84 ("drm/sched: Add new test for DRM_GPU_SCHED_STAT_NO_HANG")
> Cc: Maíra Canal <mca...@igalia.com>> Cc: Philipp Stanner 
<pha...@kernel.org>
---
  drivers/gpu/drm/scheduler/tests/mock_scheduler.c | 2 +-
  drivers/gpu/drm/scheduler/tests/sched_tests.h    | 7 ++++---
  drivers/gpu/drm/scheduler/tests/tests_basic.c    | 4 ++--
  3 files changed, 7 insertions(+), 6 deletions(-)

diff --git a/drivers/gpu/drm/scheduler/tests/mock_scheduler.c 
b/drivers/gpu/drm/scheduler/tests/mock_scheduler.c
index 65acffc3fea8..8e9ae7d980eb 100644
--- a/drivers/gpu/drm/scheduler/tests/mock_scheduler.c
+++ b/drivers/gpu/drm/scheduler/tests/mock_scheduler.c
@@ -219,7 +219,7 @@ mock_sched_timedout_job(struct drm_sched_job *sched_job)
        unsigned long flags;
  
  	if (job->flags & DRM_MOCK_SCHED_JOB_DONT_RESET) {
-               job->flags &= ~DRM_MOCK_SCHED_JOB_DONT_RESET;
+               job->flags |= DRM_MOCK_SCHED_JOB_RESET_SKIPPED;
                return DRM_GPU_SCHED_STAT_NO_HANG;
        }
  
diff --git a/drivers/gpu/drm/scheduler/tests/sched_tests.h b/drivers/gpu/drm/scheduler/tests/sched_tests.h
index 63d4f2ac7074..5b262126b776 100644
--- a/drivers/gpu/drm/scheduler/tests/sched_tests.h
+++ b/drivers/gpu/drm/scheduler/tests/sched_tests.h
@@ -95,9 +95,10 @@ struct drm_mock_sched_job {
  
  	struct completion	done;
  
-#define DRM_MOCK_SCHED_JOB_DONE		0x1
-#define DRM_MOCK_SCHED_JOB_TIMEDOUT    0x2
-#define DRM_MOCK_SCHED_JOB_DONT_RESET  0x4
+#define DRM_MOCK_SCHED_JOB_DONE                        0x1
+#define DRM_MOCK_SCHED_JOB_TIMEDOUT            0x2
+#define DRM_MOCK_SCHED_JOB_DONT_RESET          0x4
+#define DRM_MOCK_SCHED_JOB_RESET_SKIPPED       0x8
        unsigned long           flags;
  
  	struct list_head	link;
diff --git a/drivers/gpu/drm/scheduler/tests/tests_basic.c 
b/drivers/gpu/drm/scheduler/tests/tests_basic.c
index 55eb142bd7c5..82a41a456b0a 100644
--- a/drivers/gpu/drm/scheduler/tests/tests_basic.c
+++ b/drivers/gpu/drm/scheduler/tests/tests_basic.c
@@ -317,8 +317,8 @@ static void drm_sched_skip_reset(struct kunit *test)
        KUNIT_ASSERT_FALSE(test, done);
  
  	KUNIT_ASSERT_EQ(test,
-                       job->flags & DRM_MOCK_SCHED_JOB_DONT_RESET,
-                       0);
+                       job->flags & DRM_MOCK_SCHED_JOB_RESET_SKIPPED,
+                       DRM_MOCK_SCHED_JOB_RESET_SKIPPED);

Maybe we could assert that job->flags & DRM_MOCK_SCHED_JOB_TIMEDOUT == 0

Anyway, thanks for the fix!

Reviewed-by: Maíra Canal <mca...@igalia.com>

Best Regards,
- Maíra

  
  	i = drm_mock_sched_advance(sched, 1);
        KUNIT_ASSERT_EQ(test, i, 1);