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Message-ID: <53ec7656-d5d7-460e-a245-0c9598a71f26@amd.com>
Date: Thu, 4 Sep 2025 13:56:47 +0200
From: Christian König <christian.koenig@....com>
To: phasta@...nel.org, Lyude Paul <lyude@...hat.com>,
Danilo Krummrich <dakr@...nel.org>, David Airlie <airlied@...il.com>,
Simona Vetter <simona@...ll.ch>, Sumit Semwal <sumit.semwal@...aro.org>
Cc: dri-devel@...ts.freedesktop.org, nouveau@...ts.freedesktop.org,
linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2] Revert "drm/nouveau: Remove waitque for sched
teardown"
On 04.09.25 13:12, Philipp Stanner wrote:
> On Thu, 2025-09-04 at 12:27 +0200, Christian König wrote:
>> On 01.09.25 10:31, Philipp Stanner wrote:
>>> This reverts:
>>>
>>> commit bead88002227 ("drm/nouveau: Remove waitque for sched teardown")
>>> commit 5f46f5c7af8c ("drm/nouveau: Add new callback for scheduler teardown")
>>>
>>> from the drm/sched teardown leak fix series:
>>>
>>> https://lore.kernel.org/dri-devel/20250710125412.128476-2-phasta@kernel.org/
>>>
>>> The aforementioned series removed a blocking waitqueue from
>>> nouveau_sched_fini(). It was mistakenly assumed that this waitqueue only
>>> prevents jobs from leaking, which the series fixed.
>>>
>>> The waitqueue, however, also guarantees that all VM_BIND related jobs
>>> are finished in order, cleaning up mappings in the GPU's MMU. These jobs
>>> must be executed sequentially. Without the waitqueue, this is no longer
>>> guaranteed, because entity and scheduler teardown can race with each
>>> other.
>>
>> That sounds like exactly the kind of issues I tried to catch with the recent dma_fence changes.
>
> Link? :)
dma-buf: add warning when dma_fence is signaled from IOCTL
>
>>
>> Going to keep working on that and potentially using this here as blueprint for something it should catch.
>
> This is more like a nouveau-specific issue. The problem is that
> unmapping mappings in the GPU's MMU must be done in a specific order,
> and all the unmappings must be performed, not canceled.
>
> For EXEC jobs, it's perfectly fine to cancel pending jobs, remove the
> waitqueue and just rush through drm_sched_fini().
>
> I don't know the issue you're describing, but I don't think a feature
> in dma_fence could help with that specific Nouveau problem. dma_fence
> can't force the driver to submit jobs in a specific order or to wait
> until they're all completed.
Well the updates are represented by a dma_fence, aren't they?
So the dma_fence framework could potentially warn if a fence from the same context signals out of order.
Regards,
Christian.
>
> Grüße
> P.
>
>>
>> Regards,
>> Christian.
>>
>>>
>>> Revert all patches related to the waitqueue removal.
>>>
>>> Fixes: bead88002227 ("drm/nouveau: Remove waitque for sched teardown")
>>> Suggested-by: Danilo Krummrich <dakr@...nel.org>
>>> Signed-off-by: Philipp Stanner <phasta@...nel.org>
>>> ---
>>> Changes in v2:
>>> - Don't revert commit 89b2675198ab ("drm/nouveau: Make fence container helper usable driver-wide")
>>> - Add Fixes-tag
>>> ---
>>> drivers/gpu/drm/nouveau/nouveau_fence.c | 15 -----------
>>> drivers/gpu/drm/nouveau/nouveau_fence.h | 1 -
>>> drivers/gpu/drm/nouveau/nouveau_sched.c | 35 ++++++++++---------------
>>> drivers/gpu/drm/nouveau/nouveau_sched.h | 9 ++++---
>>> drivers/gpu/drm/nouveau/nouveau_uvmm.c | 8 +++---
>>> 5 files changed, 24 insertions(+), 44 deletions(-)
>>>
>>> diff --git a/drivers/gpu/drm/nouveau/nouveau_fence.c b/drivers/gpu/drm/nouveau/nouveau_fence.c
>>> index 9f345a008717..869d4335c0f4 100644
>>> --- a/drivers/gpu/drm/nouveau/nouveau_fence.c
>>> +++ b/drivers/gpu/drm/nouveau/nouveau_fence.c
>>> @@ -240,21 +240,6 @@ nouveau_fence_emit(struct nouveau_fence *fence)
>>> return ret;
>>> }
>>>
>>> -void
>>> -nouveau_fence_cancel(struct nouveau_fence *fence)
>>> -{
>>> - struct nouveau_fence_chan *fctx = nouveau_fctx(fence);
>>> - unsigned long flags;
>>> -
>>> - spin_lock_irqsave(&fctx->lock, flags);
>>> - if (!dma_fence_is_signaled_locked(&fence->base)) {
>>> - dma_fence_set_error(&fence->base, -ECANCELED);
>>> - if (nouveau_fence_signal(fence))
>>> - nvif_event_block(&fctx->event);
>>> - }
>>> - spin_unlock_irqrestore(&fctx->lock, flags);
>>> -}
>>> -
>>> bool
>>> nouveau_fence_done(struct nouveau_fence *fence)
>>> {
>>> diff --git a/drivers/gpu/drm/nouveau/nouveau_fence.h b/drivers/gpu/drm/nouveau/nouveau_fence.h
>>> index 9957a919bd38..183dd43ecfff 100644
>>> --- a/drivers/gpu/drm/nouveau/nouveau_fence.h
>>> +++ b/drivers/gpu/drm/nouveau/nouveau_fence.h
>>> @@ -29,7 +29,6 @@ void nouveau_fence_unref(struct nouveau_fence **);
>>>
>>> int nouveau_fence_emit(struct nouveau_fence *);
>>> bool nouveau_fence_done(struct nouveau_fence *);
>>> -void nouveau_fence_cancel(struct nouveau_fence *fence);
>>> int nouveau_fence_wait(struct nouveau_fence *, bool lazy, bool intr);
>>> int nouveau_fence_sync(struct nouveau_bo *, struct nouveau_channel *, bool exclusive, bool intr);
>>>
>>> diff --git a/drivers/gpu/drm/nouveau/nouveau_sched.c b/drivers/gpu/drm/nouveau/nouveau_sched.c
>>> index 0cc0bc9f9952..e60f7892f5ce 100644
>>> --- a/drivers/gpu/drm/nouveau/nouveau_sched.c
>>> +++ b/drivers/gpu/drm/nouveau/nouveau_sched.c
>>> @@ -11,7 +11,6 @@
>>> #include "nouveau_exec.h"
>>> #include "nouveau_abi16.h"
>>> #include "nouveau_sched.h"
>>> -#include "nouveau_chan.h"
>>>
>>> #define NOUVEAU_SCHED_JOB_TIMEOUT_MS 10000
>>>
>>> @@ -122,9 +121,11 @@ nouveau_job_done(struct nouveau_job *job)
>>> {
>>> struct nouveau_sched *sched = job->sched;
>>>
>>> - spin_lock(&sched->job_list.lock);
>>> + spin_lock(&sched->job.list.lock);
>>> list_del(&job->entry);
>>> - spin_unlock(&sched->job_list.lock);
>>> + spin_unlock(&sched->job.list.lock);
>>> +
>>> + wake_up(&sched->job.wq);
>>> }
>>>
>>> void
>>> @@ -305,9 +306,9 @@ nouveau_job_submit(struct nouveau_job *job)
>>> }
>>>
>>> /* Submit was successful; add the job to the schedulers job list. */
>>> - spin_lock(&sched->job_list.lock);
>>> - list_add(&job->entry, &sched->job_list.head);
>>> - spin_unlock(&sched->job_list.lock);
>>> + spin_lock(&sched->job.list.lock);
>>> + list_add(&job->entry, &sched->job.list.head);
>>> + spin_unlock(&sched->job.list.lock);
>>>
>>> drm_sched_job_arm(&job->base);
>>> job->done_fence = dma_fence_get(&job->base.s_fence->finished);
>>> @@ -392,23 +393,10 @@ nouveau_sched_free_job(struct drm_sched_job *sched_job)
>>> nouveau_job_fini(job);
>>> }
>>>
>>> -static void
>>> -nouveau_sched_cancel_job(struct drm_sched_job *sched_job)
>>> -{
>>> - struct nouveau_fence *fence;
>>> - struct nouveau_job *job;
>>> -
>>> - job = to_nouveau_job(sched_job);
>>> - fence = to_nouveau_fence(job->done_fence);
>>> -
>>> - nouveau_fence_cancel(fence);
>>> -}
>>> -
>>> static const struct drm_sched_backend_ops nouveau_sched_ops = {
>>> .run_job = nouveau_sched_run_job,
>>> .timedout_job = nouveau_sched_timedout_job,
>>> .free_job = nouveau_sched_free_job,
>>> - .cancel_job = nouveau_sched_cancel_job,
>>> };
>>>
>>> static int
>>> @@ -458,8 +446,9 @@ nouveau_sched_init(struct nouveau_sched *sched, struct nouveau_drm *drm,
>>> goto fail_sched;
>>>
>>> mutex_init(&sched->mutex);
>>> - spin_lock_init(&sched->job_list.lock);
>>> - INIT_LIST_HEAD(&sched->job_list.head);
>>> + spin_lock_init(&sched->job.list.lock);
>>> + INIT_LIST_HEAD(&sched->job.list.head);
>>> + init_waitqueue_head(&sched->job.wq);
>>>
>>> return 0;
>>>
>>> @@ -493,12 +482,16 @@ nouveau_sched_create(struct nouveau_sched **psched, struct nouveau_drm *drm,
>>> return 0;
>>> }
>>>
>>> +
>>> static void
>>> nouveau_sched_fini(struct nouveau_sched *sched)
>>> {
>>> struct drm_gpu_scheduler *drm_sched = &sched->base;
>>> struct drm_sched_entity *entity = &sched->entity;
>>>
>>> + rmb(); /* for list_empty to work without lock */
>>> + wait_event(sched->job.wq, list_empty(&sched->job.list.head));
>>> +
>>> drm_sched_entity_fini(entity);
>>> drm_sched_fini(drm_sched);
>>>
>>> diff --git a/drivers/gpu/drm/nouveau/nouveau_sched.h b/drivers/gpu/drm/nouveau/nouveau_sched.h
>>> index b98c3f0bef30..20cd1da8db73 100644
>>> --- a/drivers/gpu/drm/nouveau/nouveau_sched.h
>>> +++ b/drivers/gpu/drm/nouveau/nouveau_sched.h
>>> @@ -103,9 +103,12 @@ struct nouveau_sched {
>>> struct mutex mutex;
>>>
>>> struct {
>>> - struct list_head head;
>>> - spinlock_t lock;
>>> - } job_list;
>>> + struct {
>>> + struct list_head head;
>>> + spinlock_t lock;
>>> + } list;
>>> + struct wait_queue_head wq;
>>> + } job;
>>> };
>>>
>>> int nouveau_sched_create(struct nouveau_sched **psched, struct nouveau_drm *drm,
>>> diff --git a/drivers/gpu/drm/nouveau/nouveau_uvmm.c b/drivers/gpu/drm/nouveau/nouveau_uvmm.c
>>> index d94a85509176..79eefdfd08a2 100644
>>> --- a/drivers/gpu/drm/nouveau/nouveau_uvmm.c
>>> +++ b/drivers/gpu/drm/nouveau/nouveau_uvmm.c
>>> @@ -1019,8 +1019,8 @@ bind_validate_map_sparse(struct nouveau_job *job, u64 addr, u64 range)
>>> u64 end = addr + range;
>>>
>>> again:
>>> - spin_lock(&sched->job_list.lock);
>>> - list_for_each_entry(__job, &sched->job_list.head, entry) {
>>> + spin_lock(&sched->job.list.lock);
>>> + list_for_each_entry(__job, &sched->job.list.head, entry) {
>>> struct nouveau_uvmm_bind_job *bind_job = to_uvmm_bind_job(__job);
>>>
>>> list_for_each_op(op, &bind_job->ops) {
>>> @@ -1030,7 +1030,7 @@ bind_validate_map_sparse(struct nouveau_job *job, u64 addr, u64 range)
>>>
>>> if (!(end <= op_addr || addr >= op_end)) {
>>> nouveau_uvmm_bind_job_get(bind_job);
>>> - spin_unlock(&sched->job_list.lock);
>>> + spin_unlock(&sched->job.list.lock);
>>> wait_for_completion(&bind_job->complete);
>>> nouveau_uvmm_bind_job_put(bind_job);
>>> goto again;
>>> @@ -1038,7 +1038,7 @@ bind_validate_map_sparse(struct nouveau_job *job, u64 addr, u64 range)
>>> }
>>> }
>>> }
>>> - spin_unlock(&sched->job_list.lock);
>>> + spin_unlock(&sched->job.list.lock);
>>> }
>>>
>>> static int
>>
>
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