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

[Krzysztof Karas]

Hi Tvrtko,

> 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+
Thanks for explaining. I'll try that out then.

Krzysztof

> 
> 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)