[PATCH v2] drm/i915/gt: Ensure irqs' status does not change with spin_unlock

[Tvrtko Ursulin]

Hi,

On 14/01/2025 09:00, Krzysztof Karas wrote:
> spin_unlock() function enables irqs regardless of their state

It doesn't, you confuse spin_unlock with spin_unlock_irq.

> before spin_lock() was called. This might result in an interrupt
> while holding a lock further down in the execution, as seen in
> GitLab issue #13399.
> 
> Try to remedy the problem by saving irq state before spin lock
> acquisition.

Please check guc_lrc_desc_unpin(). It gets called from the 
destroyed_worker_func as  hinted by lockdep in 13399. There is a plain 
spin_lock() in there (in contradiction with itself). Fixing that one may 
be all that is needed to fix this correctly.

If that turns out right then also:

Fixes: 2f2cc53b5fe7 ("drm/i915/guc: Close deregister-context race 
against CT-loss")
Cc: <stable at vger.kernel.org> # v6.9+

Regards,

Tvrtko

> 
> v2: add irqs' state save/restore calls to all locks/unlocks in
>   signal_irq_work() execution (Maciej)
> 
> Signed-off-by: Krzysztof Karas <krzysztof.karas at intel.com>
> ---
> This issue is hit rarely on CI and I was not able to reproduce
> it locally. There might be more places where we should save and
> restore irq state, so I am not adding "Closes" label for the
> issue yet.
> 
>   drivers/gpu/drm/i915/gt/intel_breadcrumbs.c   | 21 ++++++++++++-------
>   .../gpu/drm/i915/gt/uc/intel_guc_submission.c |  5 +++--
>   2 files changed, 16 insertions(+), 10 deletions(-)
> 
> diff --git a/drivers/gpu/drm/i915/gt/intel_breadcrumbs.c b/drivers/gpu/drm/i915/gt/intel_breadcrumbs.c
> index cc866773ba6f..dd5542726b41 100644
> --- a/drivers/gpu/drm/i915/gt/intel_breadcrumbs.c
> +++ b/drivers/gpu/drm/i915/gt/intel_breadcrumbs.c
> @@ -53,13 +53,15 @@ static void __intel_breadcrumbs_arm_irq(struct intel_breadcrumbs *b)
>   
>   static void intel_breadcrumbs_arm_irq(struct intel_breadcrumbs *b)
>   {
> +	unsigned long flags;
> +
>   	if (!b->irq_engine)
>   		return;
>   
> -	spin_lock(&b->irq_lock);
> +	spin_lock_irqsave(&b->irq_lock, flags);
>   	if (!b->irq_armed)
>   		__intel_breadcrumbs_arm_irq(b);
> -	spin_unlock(&b->irq_lock);
> +	spin_unlock_irqrestore(&b->irq_lock, flags);
>   }
>   
>   static void __intel_breadcrumbs_disarm_irq(struct intel_breadcrumbs *b)
> @@ -76,10 +78,12 @@ static void __intel_breadcrumbs_disarm_irq(struct intel_breadcrumbs *b)
>   
>   static void intel_breadcrumbs_disarm_irq(struct intel_breadcrumbs *b)
>   {
> -	spin_lock(&b->irq_lock);
> +	unsigned long flags;
> +
> +	spin_lock_irqsave(&b->irq_lock, flags);
>   	if (b->irq_armed)
>   		__intel_breadcrumbs_disarm_irq(b);
> -	spin_unlock(&b->irq_lock);
> +	spin_unlock_irqrestore(&b->irq_lock, flags);
>   }
>   
>   static void add_signaling_context(struct intel_breadcrumbs *b,
> @@ -173,6 +177,7 @@ static void signal_irq_work(struct irq_work *work)
>   	const ktime_t timestamp = ktime_get();
>   	struct llist_node *signal, *sn;
>   	struct intel_context *ce;
> +	unsigned long flags;
>   
>   	signal = NULL;
>   	if (unlikely(!llist_empty(&b->signaled_requests)))
> @@ -226,10 +231,10 @@ static void signal_irq_work(struct irq_work *work)
>   			 * spinlock as the callback chain may end up adding
>   			 * more signalers to the same context or engine.
>   			 */
> -			spin_lock(&ce->signal_lock);
> +			spin_lock_irqsave(&ce->signal_lock, flags);
>   			list_del_rcu(&rq->signal_link);
>   			release = remove_signaling_context(b, ce);
> -			spin_unlock(&ce->signal_lock);
> +			spin_unlock_irqrestore(&ce->signal_lock, flags);
>   			if (release) {
>   				if (intel_timeline_is_last(ce->timeline, rq))
>   					add_retire(b, ce->timeline);
> @@ -254,11 +259,11 @@ static void signal_irq_work(struct irq_work *work)
>   		if (rq->engine->sched_engine->retire_inflight_request_prio)
>   			rq->engine->sched_engine->retire_inflight_request_prio(rq);
>   
> -		spin_lock(&rq->lock);
> +		spin_lock_irqsave(&rq->lock, flags);
>   		list_replace(&rq->fence.cb_list, &cb_list);
>   		__dma_fence_signal__timestamp(&rq->fence, timestamp);
>   		__dma_fence_signal__notify(&rq->fence, &cb_list);
> -		spin_unlock(&rq->lock);
> +		spin_unlock_irqrestore(&rq->lock, flags);
>   
>   		i915_request_put(rq);
>   	}
> diff --git a/drivers/gpu/drm/i915/gt/uc/intel_guc_submission.c b/drivers/gpu/drm/i915/gt/uc/intel_guc_submission.c
> index 12f1ba7ca9c1..e9102f7246f5 100644
> --- a/drivers/gpu/drm/i915/gt/uc/intel_guc_submission.c
> +++ b/drivers/gpu/drm/i915/gt/uc/intel_guc_submission.c
> @@ -4338,10 +4338,11 @@ static void guc_bump_inflight_request_prio(struct i915_request *rq,
>   static void guc_retire_inflight_request_prio(struct i915_request *rq)
>   {
>   	struct intel_context *ce = request_to_scheduling_context(rq);
> +	unsigned long flags;
>   
> -	spin_lock(&ce->guc_state.lock);
> +	spin_lock_irqsave(&ce->guc_state.lock, flags);
>   	guc_prio_fini(rq, ce);
> -	spin_unlock(&ce->guc_state.lock);
> +	spin_unlock_irqrestore(&ce->guc_state.lock, flags);
>   }
>   
>   static void sanitize_hwsp(struct intel_engine_cs *engine)