Re: [PATCH] drm/nouveau: use dedicated wq for fence uevents work

[Danilo Krummrich <dakr@redhat.com>]

On Fri, Feb 23, 2024 at 10:14:53AM +1000, Dave Airlie wrote:
> On Fri, 23 Feb 2024 at 00:45, Danilo Krummrich <dakr@redhat.com> wrote:
> >
> > Using the kernel global workqueue to signal fences can lead to
> > unexpected deadlocks. Some other work (e.g. from a different driver)
> > could directly or indirectly depend on this fence to be signaled.
> > However, if the WQ_MAX_ACTIVE limit is reached by waiters, this can
> > prevent the work signaling the fence from running.
> >
> > While this seems fairly unlikely, it's potentially exploitable.
> 
> LGTM
> 
> Reviewed-by: Dave Airlie <airlied@redhat.com>
> 
> probably should go into drm-misc-fixes?

Yes, however, 39126abc5e20 went in through drm-fixes directly it seems, since
it's not in drm-misc-fixes.

Guess you want me to cherry-pick 39126abc5e20 to drm-misc-fixes rather than take
this one through drm-fixes as well?

> 
> >
> > Fixes: 39126abc5e20 ("nouveau: offload fence uevents work to workqueue")
> > Signed-off-by: Danilo Krummrich <dakr@redhat.com>
> > ---
> >  drivers/gpu/drm/nouveau/nouveau_drm.c   | 13 +++++++++++--
> >  drivers/gpu/drm/nouveau/nouveau_drv.h   |  3 +++
> >  drivers/gpu/drm/nouveau/nouveau_fence.c |  3 ++-
> >  drivers/gpu/drm/nouveau/nouveau_fence.h |  2 ++
> >  4 files changed, 18 insertions(+), 3 deletions(-)
> >
> > diff --git a/drivers/gpu/drm/nouveau/nouveau_drm.c b/drivers/gpu/drm/nouveau/nouveau_drm.c
> > index 6f6c31a9937b..6be202081077 100644
> > --- a/drivers/gpu/drm/nouveau/nouveau_drm.c
> > +++ b/drivers/gpu/drm/nouveau/nouveau_drm.c
> > @@ -598,9 +598,15 @@ nouveau_drm_device_init(struct drm_device *dev)
> >                 goto fail_alloc;
> >         }
> >
> > +       drm->fence_wq = alloc_workqueue("nouveau_fence_wq", 0, WQ_MAX_ACTIVE);
> > +       if (!drm->fence_wq) {
> > +               ret = -ENOMEM;
> > +               goto fail_sched_wq;
> > +       }
> > +
> >         ret = nouveau_cli_init(drm, "DRM-master", &drm->master);
> >         if (ret)
> > -               goto fail_wq;
> > +               goto fail_fence_wq;
> >
> >         ret = nouveau_cli_init(drm, "DRM", &drm->client);
> >         if (ret)
> > @@ -670,7 +676,9 @@ nouveau_drm_device_init(struct drm_device *dev)
> >         nouveau_cli_fini(&drm->client);
> >  fail_master:
> >         nouveau_cli_fini(&drm->master);
> > -fail_wq:
> > +fail_fence_wq:
> > +       destroy_workqueue(drm->fence_wq);
> > +fail_sched_wq:
> >         destroy_workqueue(drm->sched_wq);
> >  fail_alloc:
> >         nvif_parent_dtor(&drm->parent);
> > @@ -725,6 +733,7 @@ nouveau_drm_device_fini(struct drm_device *dev)
> >
> >         nouveau_cli_fini(&drm->client);
> >         nouveau_cli_fini(&drm->master);
> > +       destroy_workqueue(drm->fence_wq);
> >         destroy_workqueue(drm->sched_wq);
> >         nvif_parent_dtor(&drm->parent);
> >         mutex_destroy(&drm->clients_lock);
> > diff --git a/drivers/gpu/drm/nouveau/nouveau_drv.h b/drivers/gpu/drm/nouveau/nouveau_drv.h
> > index 8a6d94c8b163..b43619a213a4 100644
> > --- a/drivers/gpu/drm/nouveau/nouveau_drv.h
> > +++ b/drivers/gpu/drm/nouveau/nouveau_drv.h
> > @@ -261,6 +261,9 @@ struct nouveau_drm {
> >         /* Workqueue used for channel schedulers. */
> >         struct workqueue_struct *sched_wq;
> >
> > +       /* Workqueue used to signal fences. */
> > +       struct workqueue_struct *fence_wq;
> > +
> >         /* context for accelerated drm-internal operations */
> >         struct nouveau_channel *cechan;
> >         struct nouveau_channel *channel;
> > diff --git a/drivers/gpu/drm/nouveau/nouveau_fence.c b/drivers/gpu/drm/nouveau/nouveau_fence.c
> > index 93f08f9479d8..c3ea3cd933cd 100644
> > --- a/drivers/gpu/drm/nouveau/nouveau_fence.c
> > +++ b/drivers/gpu/drm/nouveau/nouveau_fence.c
> > @@ -174,7 +174,7 @@ static int
> >  nouveau_fence_wait_uevent_handler(struct nvif_event *event, void *repv, u32 repc)
> >  {
> >         struct nouveau_fence_chan *fctx = container_of(event, typeof(*fctx), event);
> > -       schedule_work(&fctx->uevent_work);
> > +       queue_work(fctx->wq, &fctx->uevent_work);
> >         return NVIF_EVENT_KEEP;
> >  }
> >
> > @@ -194,6 +194,7 @@ nouveau_fence_context_new(struct nouveau_channel *chan, struct nouveau_fence_cha
> >         INIT_LIST_HEAD(&fctx->pending);
> >         spin_lock_init(&fctx->lock);
> >         fctx->context = chan->drm->runl[chan->runlist].context_base + chan->chid;
> > +       fctx->wq = chan->drm->fence_wq;
> >
> >         if (chan == chan->drm->cechan)
> >                 strcpy(fctx->name, "copy engine channel");
> > diff --git a/drivers/gpu/drm/nouveau/nouveau_fence.h b/drivers/gpu/drm/nouveau/nouveau_fence.h
> > index 8bc065acfe35..bc13110bdfa4 100644
> > --- a/drivers/gpu/drm/nouveau/nouveau_fence.h
> > +++ b/drivers/gpu/drm/nouveau/nouveau_fence.h
> > @@ -44,7 +44,9 @@ struct nouveau_fence_chan {
> >         u32 context;
> >         char name[32];
> >
> > +       struct workqueue_struct *wq;
> >         struct work_struct uevent_work;
> > +
> >         struct nvif_event event;
> >         int notify_ref, dead, killed;
> >  };
> >
> > base-commit: 1f4c6f11a557642505e5f403e0dfabbaff9c529a
> > --
> > 2.43.0
> >
>