On Fri, 23 Feb 2024 at 00:45, Danilo Krummrich <dakr@xxxxxxxxxx> 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@xxxxxxxxxx>
probably should go into drm-misc-fixes?
>
> Fixes: 39126abc5e20 ("nouveau: offload fence uevents work to workqueue")
> Signed-off-by: Danilo Krummrich <dakr@xxxxxxxxxx>
> ---
> 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
>
