[PATCH] drm/sched: Discourage usage of separate workqueues

[Danilo Krummrich]

On Wed, Jun 04, 2025 at 09:45:00AM -0700, Matthew Brost wrote:
> On Wed, Jun 04, 2025 at 05:07:15PM +0200, Simona Vetter wrote:
> > We should definitely document this trick better though, I didn't find any
> > place where that was documented.
> 
> This is a good idea.

I think - and I also mentioned this a few times in the patch series that added
the workqueue support - we should also really document the pitfalls of this.

If the scheduler shares a workqueue with the driver, the driver needs to take
special care when submitting work that it's not possible to prevent run_job and
free_job work from running by doing this.

For instance, if it's a single threaded workqueue and the driver submits work
that allocates with GFP_KERNEL, this is a deadlock condition.

More generally, if the driver submits N work that, for instance allocates with
GFP_KERNEL, it's also a deadlock condition if N == max_active.