Re: [PATCH v2 01/12] drm/panfrost: Make sure MMU context lifetime is not bound to panfrost_priv

[Boris Brezillon <boris.brezillon@collabora.com>]

On Mon, 21 Jun 2021 15:29:55 +0100
Steven Price <steven.price@arm.com> wrote:

> On 21/06/2021 14:57, Alyssa Rosenzweig wrote:
> >> Jobs can be in-flight when the file descriptor is closed (either because
> >> the process did not terminate properly, or because it didn't wait for
> >> all GPU jobs to be finished), and apparently panfrost_job_close() does
> >> not cancel already running jobs. Let's refcount the MMU context object
> >> so it's lifetime is no longer bound to the FD lifetime and running jobs
> >> can finish properly without generating spurious page faults.  
> > 
> > Remind me - why can't we hard stop in-flight jobs when the fd is closed?
> > I've seen cases where kill -9'ing a badly behaved process doesn't end
> > the fault storm, or unfreeze the desktop.
> >   
> 
> Hard-stopping the in-flight jobs would also make sense. But unless we
> want to actually hang the close() then there will be a period between
> issuing the hard-stop and actually having completed all jobs in the context.

Patch 10 is doing that, I just didn't want to backport all the
dependencies, so I kept it split in 2 halves: one patch fixing the
use-after-free bug, and the other part killing in-flight jobs.

> 
> But equally to be fair I've been cherry-picking this patch myself for
> quite some time, so we should just merge it and improve from there. So
> you can have my:
> 
> Reviewed-by: Steven Price <steven.price@arm.com>