On 11/8/23 06:46, Luben Tuikov wrote:
Hi,
Could you please use my gmail address, the one one I'm responding from--I don't want
to miss any DRM scheduler patches. BTW, the luben.tuikov@xxxxxxx email should bounce
as undeliverable.
On 2023-11-07 21:26, Danilo Krummrich wrote:
Commit 56e449603f0a ("drm/sched: Convert the GPU scheduler to variable
number of run-queues") introduces drm_err() in drm_sched_job_init(), in
order to indicate that the given entity has no runq, however at this
time job->sched is not yet set, likely to be NULL initialized, and hence
shouldn't be used.
Replace the corresponding drm_err() call with pr_err() to avoid a
potential page fault.
While at it, extend the documentation of drm_sched_job_init() to
indicate that job->sched is not a valid pointer until
drm_sched_job_arm() has been called.
Fixes: 56e449603f0a ("drm/sched: Convert the GPU scheduler to variable number of run-queues")
Signed-off-by: Danilo Krummrich <dakr@xxxxxxxxxx>
---
drivers/gpu/drm/scheduler/sched_main.c | 5 ++++-
1 file changed, 4 insertions(+), 1 deletion(-)
diff --git a/drivers/gpu/drm/scheduler/sched_main.c b/drivers/gpu/drm/scheduler/sched_main.c
index 27843e37d9b7..dd28389f0ddd 100644
--- a/drivers/gpu/drm/scheduler/sched_main.c
+++ b/drivers/gpu/drm/scheduler/sched_main.c
@@ -680,6 +680,9 @@ EXPORT_SYMBOL(drm_sched_resubmit_jobs);
* This function returns -ENOENT in this case (which probably should be -EIO as
* a more meanigful return value).
*
+ * Note that job->sched is not a valid pointer until drm_sched_job_arm() has
+ * been called.
+ *
Good catch!
Did you actually get this to page-fault and have a kernel log?
No, I just found it because I was about to make the same mistake.
I'm asking because we see it correctly set in this kernel log coming from AMD,
I think that's because amdgpu just sets job->sched to *some* scheduler instance after
job allocation [1].
[1] https://elixir.bootlin.com/linux/latest/source/drivers/gpu/drm/amd/amdgpu/amdgpu_job.c#L108
[ 11.886024] amdgpu 0000:0a:00.0: [drm] *ERROR* drm_sched_job_init: entity has no rq!
in this email,
https://lore.kernel.org/r/CADnq5_PS64jYS_Y3kGW27m-kuWP+FQFiaVcOaZiB=JLSgPnXBQ@xxxxxxxxxxxxxx
* Returns 0 for success, negative error code otherwise.
*/
int drm_sched_job_init(struct drm_sched_job *job,
@@ -691,7 +694,7 @@ int drm_sched_job_init(struct drm_sched_job *job,
* or worse--a blank screen--leave a trail in the
* logs, so this can be debugged easier.
*/
- drm_err(job->sched, "%s: entity has no rq!\n", __func__);
+ pr_err("%s: entity has no rq!\n", __func__);
Is it feasible to do something like the following?
dev_err(job->sched ? job->sched->dev : NULL, "%s: entity has no rq!\n", __func__);
I don't think that's a good idea. Although I'd assume that every driver zero-initializes its job
structures, I can't see a rule enforcing that. Hence, job->sched can be a random value until
drm_sched_job_arm() is called.
However, I notice there are quite a view more fields of struct drm_sched_job that are never
initialized, hence there are either a couple more potential bugs or missing documentation that
drivers *must* ensure that a job is zero-initialized.
Not quite sure if we really want to rely on the latter for core infrastructure...
return -ENOENT;
}
base-commit: c015fb6d01adb616fb54824feb55ce5ab18e8ca1
