On 07/07/2026 12:48, Marco Pagani wrote:
Currently, the mock scheduler uses KUnit-managed memory for jobs. This ties
the job's memory lifetime to the test suite rather than the DRM scheduler's
callbacks. This does not represent real driver behavior and can lead to
potential Use-After-Free bugs in the tests.
Since you say use-after-free, that means something belonging to a test
wasn't properly cleaned up, right? Could you help me out review by
describing one example?
Idea was that tests are self contained, ie. when a tests exits it is
guaranteed all resources belonging to it are gone. Everything else
should be a test bug which IMO means it is fine to crash if a new tests
gets that wrong. Just idle at the end of the test and everything should
work.
Update the mock scheduler to let the lifetime of jobs be managed by the DRM
scheduler's asynchronous callbacks instead of KUnit managed memory. Add a
kref reference counter to track the job's lifetime between test suites and
the scheduler.
Finally, to avoid memory leaks in the event of an early test abortion,
register a cleanup KUnit action that automatically puts the reference to
the job.
So kunit managed memory, freed on test exit, is replaced by kunit
managed actions, which also free on test exit?
Some random thoughts below while I wait to understand the motivation and
problem statement better:
Signed-off-by: Marco Pagani <[email protected]>
---
.../gpu/drm/scheduler/tests/mock_scheduler.c | 68 ++++++++++++++-----
drivers/gpu/drm/scheduler/tests/sched_tests.h | 6 ++
2 files changed, 57 insertions(+), 17 deletions(-)
diff --git a/drivers/gpu/drm/scheduler/tests/mock_scheduler.c
b/drivers/gpu/drm/scheduler/tests/mock_scheduler.c
index 14403a762335..51f81082f37a 100644
--- a/drivers/gpu/drm/scheduler/tests/mock_scheduler.c
+++ b/drivers/gpu/drm/scheduler/tests/mock_scheduler.c
@@ -96,6 +96,14 @@ drm_mock_sched_job_signal_timer(struct hrtimer *hrtimer)
return HRTIMER_NORESTART;
}
+static void drm_mock_sched_job_cleanup_action(void *ptr)
+{
+ struct drm_mock_sched_job *job = ptr;
+
+ job->test = NULL;
+ drm_mock_sched_job_put(job);
+}
+
/**
* drm_mock_sched_job_new - Create a new mock scheduler job
*
@@ -111,23 +119,34 @@ drm_mock_sched_job_new(struct kunit *test,
struct drm_mock_sched_job *job;
int ret;
- job = kunit_kzalloc(test, sizeof(*job), GFP_KERNEL);
+ /* Let the DRM Scheduler manage the lifetime of the job */
However that does not match real driver behaviour either (circling back
to the justification from the commit message). It is the drivers which
own this memory, not the DRM scheduler. So in this case mock scheduler,
which is a kunit test client, etc.
+ job = kzalloc_obj(*job, GFP_KERNEL);
KUNIT_ASSERT_NOT_NULL(test, job);
+ kref_init(&job->refcount);
+ job->test = test;
+
ret = drm_sched_job_init(&job->base,
&entity->base,
1,
NULL,
1);
- KUNIT_ASSERT_EQ(test, ret, 0);
-
- job->test = test;
+ if (ret) {
+ kfree(job);
+ KUNIT_ASSERT_EQ_MSG(test, ret, 0, "drm_sched_job_init failed");
+ }
init_completion(&job->done);
INIT_LIST_HEAD(&job->link);
hrtimer_setup(&job->timer, drm_mock_sched_job_signal_timer,
CLOCK_MONOTONIC, HRTIMER_MODE_ABS);
+ ret = kunit_add_action(test, drm_mock_sched_job_cleanup_action, job);
+ if (ret) {
+ drm_mock_sched_job_put(job);
+ KUNIT_ASSERT_EQ_MSG(test, ret, 0, "kunit_add_action failed");
+ }
+
return job;
}
@@ -152,7 +171,7 @@ static void drm_mock_sched_hw_fence_release(struct dma_fence *fence)
hrtimer_cancel(&job->timer);
- /* Containing job is freed by the kunit framework */
+ drm_mock_sched_job_put(job);
}
static const struct dma_fence_ops drm_mock_sched_hw_fence_ops = {
@@ -173,6 +192,8 @@ static struct dma_fence *mock_sched_run_job(struct
drm_sched_job *sched_job)
sched->hw_timeline.context,
atomic_inc_return(&sched->hw_timeline.next_seqno));
+ kref_get(&job->refcount);
+
dma_fence_get(&job->hw_fence); /* Reference for the job_list */
spin_lock_irq(&sched->lock);
@@ -200,6 +221,17 @@ static struct dma_fence *mock_sched_run_job(struct
drm_sched_job *sched_job)
return &job->hw_fence;
}
+static void mock_sched_free_job(struct drm_sched_job *sched_job)
+{
Free which is actually a reference put is non-obvious API.
+ struct drm_mock_sched_job *job = drm_sched_job_to_mock_job(sched_job);
+
+ /* Only if the fence has been successfully initialized */
+ if (job->hw_fence.ops)
+ dma_fence_put(&job->hw_fence);
+
+ drm_mock_sched_job_put(job);
+}
+
/*
* Normally, drivers would take appropriate measures in this callback, such as
* killing the entity the faulty job is associated with, resetting the
hardware
@@ -232,21 +264,26 @@ mock_sched_timedout_job(struct drm_sched_job *sched_job)
}
spin_unlock_irqrestore(&sched->lock, flags);
- dma_fence_put(&job->hw_fence);
- drm_sched_job_cleanup(sched_job);
- /* Mock job itself is freed by the kunit framework. */
+ mock_sched_free_job(sched_job);
return DRM_GPU_SCHED_STAT_RESET;
}
-static void mock_sched_free_job(struct drm_sched_job *sched_job)
+static void drm_mock_sched_job_release(struct kref *ref)
{
- struct drm_mock_sched_job *job = drm_sched_job_to_mock_job(sched_job);
+ struct drm_mock_sched_job *job;
+
+ job = container_of(ref, struct drm_mock_sched_job, refcount);
- dma_fence_put(&job->hw_fence);
- drm_sched_job_cleanup(sched_job);
+ drm_sched_job_cleanup(&job->base);
- /* Mock job itself is freed by the kunit framework. */
+ kfree(job);
+}
+
+void drm_mock_sched_job_put(struct drm_mock_sched_job *job)
+{
+ if (job)
+ kref_put(&job->refcount, drm_mock_sched_job_release);
}
static void mock_sched_cancel_job(struct drm_sched_job *sched_job)
@@ -265,10 +302,7 @@ static void mock_sched_cancel_job(struct drm_sched_job
*sched_job)
}
spin_unlock_irqrestore(&sched->lock, flags);
- /*
- * The GPU Scheduler will call drm_sched_backend_ops.free_job(), still.
- * Mock job itself is freed by the kunit framework.
- */
+ /* The GPU Scheduler will call drm_sched_backend_ops.free_job() */
}
static const struct drm_sched_backend_ops drm_mock_scheduler_ops = {
diff --git a/drivers/gpu/drm/scheduler/tests/sched_tests.h
b/drivers/gpu/drm/scheduler/tests/sched_tests.h
index 553d45abd057..e4d33f0bf935 100644
--- a/drivers/gpu/drm/scheduler/tests/sched_tests.h
+++ b/drivers/gpu/drm/scheduler/tests/sched_tests.h
@@ -13,6 +13,7 @@
#include <linux/list.h>
#include <linux/mutex.h>
#include <linux/types.h>
+#include <linux/kref.h>
#include <drm/gpu_scheduler.h>
@@ -90,6 +91,7 @@ struct drm_mock_sched_entity {
*/
struct drm_mock_sched_job {
struct drm_sched_job base;
+ struct kref refcount;
struct completion done;
@@ -144,6 +146,8 @@ struct drm_mock_sched_job *
drm_mock_sched_job_new(struct kunit *test,
struct drm_mock_sched_entity *entity);
+void drm_mock_sched_job_put(struct drm_mock_sched_job *job);
+
/**
* drm_mock_sched_job_submit - Arm and submit a job in one go
*
@@ -151,6 +155,8 @@ drm_mock_sched_job_new(struct kunit *test,
*/
static inline void drm_mock_sched_job_submit(struct drm_mock_sched_job *job)
{
+ kref_get(&job->refcount);
+
This feels fragile because if someone writes a test which uses arm+push
directly bad things will happen. What is this extra reference for versus
the one obtained by creating a job?
Regards,
Tvrtko
drm_sched_job_arm(&job->base);
drm_sched_entity_push_job(&job->base);
}
