Messages in this thread | ![/](/images/icornerl.gif) | | Date | Thu, 9 Nov 2023 01:09:33 +0100 | Subject | Re: [PATCH] drm/sched: fix potential page fault in drm_sched_job_init() | From | Danilo Krummrich <> |
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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@amd.com 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@redhat.com> >> --- >> 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@mail.gmail.com > >> * 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 >
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