drivers/gpu/drm/scheduler/tests/mock_scheduler.c | 14 ++++++++++++++ drivers/gpu/drm/scheduler/tests/sched_tests.h | 2 ++ 2 files changed, 16 insertions(+)
From: Shixiong Ou <oushixiong@kylinos.cn>
The DRM scheduler KUnit tests currently pass NULL for the dev field in
drm_sched_init_args, which causes a NULL pointer dereference in the
drm_sched_job trace event when it calls dev_name() on sched->dev.
Use faux_device_create() to create a fake device for the mock scheduler,
so the scheduler always has a valid device pointer. This avoids the
trace event crash without requiring the production code to accept a NULL
device pointer, which conceptually makes no sense for a scheduler.
An atomic counter is used to generate unique device names, since
multiple mock schedulers can exist simultaneously across different
test suites.
Signed-off-by: Shixiong Ou <oushixiong@kylinos.cn>
---
drivers/gpu/drm/scheduler/tests/mock_scheduler.c | 14 ++++++++++++++
drivers/gpu/drm/scheduler/tests/sched_tests.h | 2 ++
2 files changed, 16 insertions(+)
diff --git a/drivers/gpu/drm/scheduler/tests/mock_scheduler.c b/drivers/gpu/drm/scheduler/tests/mock_scheduler.c
index 14403a762335..cd87e405bb1e 100644
--- a/drivers/gpu/drm/scheduler/tests/mock_scheduler.c
+++ b/drivers/gpu/drm/scheduler/tests/mock_scheduler.c
@@ -1,6 +1,8 @@
// SPDX-License-Identifier: GPL-2.0
/* Copyright (c) 2025 Valve Corporation */
+#include <linux/device/faux.h>
+
#include "sched_tests.h"
/*
@@ -10,6 +12,8 @@
* Test cases are implemented in a separate file.
*/
+static atomic_t drm_mock_sched_instance = ATOMIC_INIT(0);
+
/**
* drm_mock_sched_entity_new - Create a new mock scheduler entity
*
@@ -296,11 +300,20 @@ struct drm_mock_scheduler *drm_mock_sched_new(struct kunit *test, long timeout)
.name = "drm-mock-scheduler",
};
struct drm_mock_scheduler *sched;
+ char name[64];
int ret;
sched = kunit_kzalloc(test, sizeof(*sched), GFP_KERNEL);
KUNIT_ASSERT_NOT_NULL(test, sched);
+ snprintf(name, sizeof(name), "drm-mock-scheduler-%d",
+ atomic_inc_return(&drm_mock_sched_instance));
+
+ sched->faux_dev = faux_device_create(name, NULL, NULL);
+ KUNIT_ASSERT_NOT_NULL(test, sched->faux_dev);
+
+ args.dev = &sched->faux_dev->dev;
+
ret = drm_sched_init(&sched->base, &args);
KUNIT_ASSERT_EQ(test, ret, 0);
@@ -323,6 +336,7 @@ struct drm_mock_scheduler *drm_mock_sched_new(struct kunit *test, long timeout)
void drm_mock_sched_fini(struct drm_mock_scheduler *sched)
{
drm_sched_fini(&sched->base);
+ faux_device_destroy(sched->faux_dev);
}
/**
diff --git a/drivers/gpu/drm/scheduler/tests/sched_tests.h b/drivers/gpu/drm/scheduler/tests/sched_tests.h
index 553d45abd057..bbf4da585866 100644
--- a/drivers/gpu/drm/scheduler/tests/sched_tests.h
+++ b/drivers/gpu/drm/scheduler/tests/sched_tests.h
@@ -7,6 +7,7 @@
#include <kunit/test.h>
#include <linux/atomic.h>
#include <linux/completion.h>
+#include <linux/device/faux.h>
#include <linux/dma-fence.h>
#include <linux/hrtimer.h>
#include <linux/ktime.h>
@@ -44,6 +45,7 @@ struct drm_mock_scheduler {
struct drm_gpu_scheduler base;
struct kunit *test;
+ struct faux_device *faux_dev;
spinlock_t lock;
struct list_head job_list;
--
2.25.1
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On Thu, Sep 03, 2026 at 05:02:56PM +0800, oushixiong1025@163.com wrote:
> From: Shixiong Ou <oushixiong@kylinos.cn>
>
> The DRM scheduler KUnit tests currently pass NULL for the dev field in
> drm_sched_init_args, which causes a NULL pointer dereference in the
> drm_sched_job trace event when it calls dev_name() on sched->dev.
>
> Use faux_device_create() to create a fake device for the mock scheduler,
> so the scheduler always has a valid device pointer. This avoids the
> trace event crash without requiring the production code to accept a NULL
> device pointer, which conceptually makes no sense for a scheduler.
>
> An atomic counter is used to generate unique device names, since
> multiple mock schedulers can exist simultaneously across different
> test suites.
>
> Signed-off-by: Shixiong Ou <oushixiong@kylinos.cn>
> ---
> drivers/gpu/drm/scheduler/tests/mock_scheduler.c | 14 ++++++++++++++
> drivers/gpu/drm/scheduler/tests/sched_tests.h | 2 ++
> 2 files changed, 16 insertions(+)
>
> diff --git a/drivers/gpu/drm/scheduler/tests/mock_scheduler.c b/drivers/gpu/drm/scheduler/tests/mock_scheduler.c
> index 14403a762335..cd87e405bb1e 100644
> --- a/drivers/gpu/drm/scheduler/tests/mock_scheduler.c
> +++ b/drivers/gpu/drm/scheduler/tests/mock_scheduler.c
> @@ -1,6 +1,8 @@
> // SPDX-License-Identifier: GPL-2.0
> /* Copyright (c) 2025 Valve Corporation */
>
> +#include <linux/device/faux.h>
> +
> #include "sched_tests.h"
>
> /*
> @@ -10,6 +12,8 @@
> * Test cases are implemented in a separate file.
> */
>
> +static atomic_t drm_mock_sched_instance = ATOMIC_INIT(0);
> +
> /**
> * drm_mock_sched_entity_new - Create a new mock scheduler entity
> *
> @@ -296,11 +300,20 @@ struct drm_mock_scheduler *drm_mock_sched_new(struct kunit *test, long timeout)
> .name = "drm-mock-scheduler",
> };
> struct drm_mock_scheduler *sched;
> + char name[64];
> int ret;
>
> sched = kunit_kzalloc(test, sizeof(*sched), GFP_KERNEL);
> KUNIT_ASSERT_NOT_NULL(test, sched);
>
> + snprintf(name, sizeof(name), "drm-mock-scheduler-%d",
> + atomic_inc_return(&drm_mock_sched_instance));
> +
> + sched->faux_dev = faux_device_create(name, NULL, NULL);
> + KUNIT_ASSERT_NOT_NULL(test, sched->faux_dev);
> +
> + args.dev = &sched->faux_dev->dev;
> +
> ret = drm_sched_init(&sched->base, &args);
> KUNIT_ASSERT_EQ(test, ret, 0);
>
> @@ -323,6 +336,7 @@ struct drm_mock_scheduler *drm_mock_sched_new(struct kunit *test, long timeout)
> void drm_mock_sched_fini(struct drm_mock_scheduler *sched)
> {
> drm_sched_fini(&sched->base);
> + faux_device_destroy(sched->faux_dev);
> }
What's wrong with drm_kunit_helper_alloc_device(), or kunit_device_register()?
Maxime
On Thu Sep 3, 2026 at 11:36 AM CEST, Maxime Ripard wrote: > What's wrong with drm_kunit_helper_alloc_device(), or kunit_device_register()? That's probably may bad, in a previous patch that tried to support a NULL device in the scheduler instead I mistakenly mentioned faux while making the point that we should use some mock device instead. Thanks, Danilo
On Thu, 2026-09-03 at 17:02 +0800, oushixiong1025@163.com wrote: > From: Shixiong Ou <oushixiong@kylinos.cn> > > The DRM scheduler KUnit tests currently pass NULL for the dev field in > drm_sched_init_args, which causes a NULL pointer dereference in the > drm_sched_job trace event when it calls dev_name() on sched->dev. > > Use faux_device_create() to create a fake device for the mock scheduler, > so the scheduler always has a valid device pointer. This avoids the > trace event crash without requiring the production code to accept a NULL > device pointer, which conceptually makes no sense for a scheduler. > > An atomic counter is used to generate unique device names, since > multiple mock schedulers can exist simultaneously across different > test suites. > > Signed-off-by: Shixiong Ou <oushixiong@kylinos.cn> Didn't you address a fault / bug with that? Cc: stable … Fixes: ? > --- > […] > > +static atomic_t drm_mock_sched_instance = ATOMIC_INIT(0); > + > /** > * drm_mock_sched_entity_new - Create a new mock scheduler entity > * > @@ -296,11 +300,20 @@ struct drm_mock_scheduler *drm_mock_sched_new(struct kunit *test, long timeout) > .name = "drm-mock-scheduler", > }; > struct drm_mock_scheduler *sched; > + char name[64]; > int ret; > > sched = kunit_kzalloc(test, sizeof(*sched), GFP_KERNEL); > KUNIT_ASSERT_NOT_NULL(test, sched); > > + snprintf(name, sizeof(name), "drm-mock-scheduler-%d", You could use args.name here. > + atomic_inc_return(&drm_mock_sched_instance)); Couldn't that atomic be a `static unsigned int` inside this function? Is simpler and limits the scope. And I wouldn't expect that we'll ever call drm_mock_sched_new() multi-threaded, or would we? Besides looks cool, thx P.
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