Re: [Intel-gfx] [PATCH 21/27] drm/i915/guc: Proper xarray usage for contexts_lookup

[Daniele Ceraolo Spurio <daniele.ceraolospurio@intel.com>]

On 8/25/2021 5:41 PM, Matthew Brost wrote:
> On Wed, Aug 25, 2021 at 05:44:11PM -0700, Daniele Ceraolo Spurio wrote:
>>
>> On 8/18/2021 11:16 PM, Matthew Brost wrote:
>>> Lock the xarray and take ref to the context if needed.
>>>
>>> v2:
>>>    (Checkpatch)
>>>     - Add new line after declaration
>>>    (Daniel Vetter)
>>>     - Correct put / get accounting in xa_for_loops
>>>
>>> Signed-off-by: Matthew Brost <matthew.brost@intel.com>
>>> ---
>>>    .../gpu/drm/i915/gt/uc/intel_guc_submission.c | 103 +++++++++++++++---
>>>    1 file changed, 88 insertions(+), 15 deletions(-)
>>>
>>> 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 509b298e7cf3..5f77f25322ca 100644
>>> --- a/drivers/gpu/drm/i915/gt/uc/intel_guc_submission.c
>>> +++ b/drivers/gpu/drm/i915/gt/uc/intel_guc_submission.c
>>> @@ -606,8 +606,18 @@ static void scrub_guc_desc_for_outstanding_g2h(struct intel_guc *guc)
>>>    	unsigned long index, flags;
>>>    	bool pending_disable, pending_enable, deregister, destroyed, banned;
>>> +	xa_lock_irqsave(&guc->context_lookup, flags);
>>>    	xa_for_each(&guc->context_lookup, index, ce) {
>>> -		spin_lock_irqsave(&ce->guc_state.lock, flags);
>>> +		/*
>>> +		 * Corner case where the ref count on the object is zero but and
>>> +		 * deregister G2H was lost. In this case we don't touch the ref
>>> +		 * count and finish the destroy of the context.
>>> +		 */
>>> +		bool do_put = kref_get_unless_zero(&ce->ref);
>>> +
>>> +		xa_unlock(&guc->context_lookup);
>>> +
>>> +		spin_lock(&ce->guc_state.lock);
>>>    		/*
>>>    		 * Once we are at this point submission_disabled() is guaranteed
>>> @@ -623,7 +633,9 @@ static void scrub_guc_desc_for_outstanding_g2h(struct intel_guc *guc)
>>>    		banned = context_banned(ce);
>>>    		init_sched_state(ce);
>>> -		spin_unlock_irqrestore(&ce->guc_state.lock, flags);
>>> +		spin_unlock(&ce->guc_state.lock);
>>> +
>>> +		GEM_BUG_ON(!do_put && !destroyed);
>>>    		if (pending_enable || destroyed || deregister) {
>>>    			decr_outstanding_submission_g2h(guc);
>>> @@ -646,13 +658,19 @@ static void scrub_guc_desc_for_outstanding_g2h(struct intel_guc *guc)
>>>    			}
>>>    			intel_context_sched_disable_unpin(ce);
>>>    			decr_outstanding_submission_g2h(guc);
>>> -			spin_lock_irqsave(&ce->guc_state.lock, flags);
>>> +
>>> +			spin_lock(&ce->guc_state.lock);
>>>    			guc_blocked_fence_complete(ce);
>>> -			spin_unlock_irqrestore(&ce->guc_state.lock, flags);
>>> +			spin_unlock(&ce->guc_state.lock);
>>>    			intel_context_put(ce);
>>>    		}
>>> +
>>> +		if (do_put)
>>> +			intel_context_put(ce);
>> is it safe to do the put outside the xa_lock, in case the refcount goes to
>> zero with this? I know it is unlikely because the refcount was > 0 if do_put
>> is true, but it might've gone down between us checking earlier and now.
>>
> It is safe as xa_for_each indicates it is safe to destroy / delete
> objects from the array while traversing it.

ok.

Reviewed-by: Daniele Ceraolo Spurio <daniele.ceraolospurio@intel.com>

Daniele

>>> +		xa_lock(&guc->context_lookup);
>>>    	}
>>> +	xa_unlock_irqrestore(&guc->context_lookup, flags);
>>>    }
>>>    static inline bool
>>> @@ -873,16 +891,29 @@ void intel_guc_submission_reset(struct intel_guc *guc, bool stalled)
>>>    {
>>>    	struct intel_context *ce;
>>>    	unsigned long index;
>>> +	unsigned long flags;
>>>    	if (unlikely(!guc_submission_initialized(guc))) {
>>>    		/* Reset called during driver load? GuC not yet initialised! */
>>>    		return;
>>>    	}
>>> -	xa_for_each(&guc->context_lookup, index, ce)
>>> +	xa_lock_irqsave(&guc->context_lookup, flags);
>>> +	xa_for_each(&guc->context_lookup, index, ce) {
>>> +		if (!kref_get_unless_zero(&ce->ref))
>>> +			continue;
>>> +
>>> +		xa_unlock(&guc->context_lookup);
>>> +
>>>    		if (intel_context_is_pinned(ce))
>>>    			__guc_reset_context(ce, stalled);
>>> +		intel_context_put(ce);
>>> +
>>> +		xa_lock(&guc->context_lookup);
>>> +	}
>>> +	xa_unlock_irqrestore(&guc->context_lookup, flags);
>>> +
>>>    	/* GuC is blown away, drop all references to contexts */
>>>    	xa_destroy(&guc->context_lookup);
>>>    }
>>> @@ -957,11 +988,24 @@ void intel_guc_submission_cancel_requests(struct intel_guc *guc)
>>>    {
>>>    	struct intel_context *ce;
>>>    	unsigned long index;
>>> +	unsigned long flags;
>>> +
>>> +	xa_lock_irqsave(&guc->context_lookup, flags);
>>> +	xa_for_each(&guc->context_lookup, index, ce) {
>>> +		if (!kref_get_unless_zero(&ce->ref))
>>> +			continue;
>>> +
>>> +		xa_unlock(&guc->context_lookup);
>>> -	xa_for_each(&guc->context_lookup, index, ce)
>>>    		if (intel_context_is_pinned(ce))
>>>    			guc_cancel_context_requests(ce);
>>> +		intel_context_put(ce);
>>> +
>>> +		xa_lock(&guc->context_lookup);
>>> +	}
>>> +	xa_unlock_irqrestore(&guc->context_lookup, flags);
>>> +
>>>    	guc_cancel_sched_engine_requests(guc->sched_engine);
>>>    	/* GuC is blown away, drop all references to contexts */
>>> @@ -2850,21 +2894,28 @@ void intel_guc_find_hung_context(struct intel_engine_cs *engine)
>>>    	struct intel_context *ce;
>>>    	struct i915_request *rq;
>>>    	unsigned long index;
>>> +	unsigned long flags;
>>>    	/* Reset called during driver load? GuC not yet initialised! */
>>>    	if (unlikely(!guc_submission_initialized(guc)))
>>>    		return;
>>> +	xa_lock_irqsave(&guc->context_lookup, flags);
>>>    	xa_for_each(&guc->context_lookup, index, ce) {
>>> -		if (!intel_context_is_pinned(ce))
>>> +		if (!kref_get_unless_zero(&ce->ref))
>>>    			continue;
>>> +		xa_unlock(&guc->context_lookup);
>>> +
>>> +		if (!intel_context_is_pinned(ce))
>>> +			goto next;
>>> +
>>>    		if (intel_engine_is_virtual(ce->engine)) {
>>>    			if (!(ce->engine->mask & engine->mask))
>>> -				continue;
>>> +				goto next;
>>>    		} else {
>>>    			if (ce->engine != engine)
>>> -				continue;
>>> +				goto next;
>>>    		}
>>>    		list_for_each_entry(rq, &ce->guc_active.requests, sched.link) {
>>> @@ -2874,9 +2925,17 @@ void intel_guc_find_hung_context(struct intel_engine_cs *engine)
>>>    			intel_engine_set_hung_context(engine, ce);
>>>    			/* Can only cope with one hang at a time... */
>>> -			return;
>>> +			intel_context_put(ce);
>>> +			xa_lock(&guc->context_lookup);
>>> +			goto done;
>>>    		}
>>> +next:
>>> +		intel_context_put(ce);
>>> +		xa_lock(&guc->context_lookup);
>>> +
>> nit: extra newline
>>
> Checkpatch got that one too. Already fixed.
>
> Matt
>
>> Daniele
>>
>>>    	}
>>> +done:
>>> +	xa_unlock_irqrestore(&guc->context_lookup, flags);
>>>    }
>>>    void intel_guc_dump_active_requests(struct intel_engine_cs *engine,
>>> @@ -2892,23 +2951,34 @@ void intel_guc_dump_active_requests(struct intel_engine_cs *engine,
>>>    	if (unlikely(!guc_submission_initialized(guc)))
>>>    		return;
>>> +	xa_lock_irqsave(&guc->context_lookup, flags);
>>>    	xa_for_each(&guc->context_lookup, index, ce) {
>>> -		if (!intel_context_is_pinned(ce))
>>> +		if (!kref_get_unless_zero(&ce->ref))
>>>    			continue;
>>> +		xa_unlock(&guc->context_lookup);
>>> +
>>> +		if (!intel_context_is_pinned(ce))
>>> +			goto next;
>>> +
>>>    		if (intel_engine_is_virtual(ce->engine)) {
>>>    			if (!(ce->engine->mask & engine->mask))
>>> -				continue;
>>> +				goto next;
>>>    		} else {
>>>    			if (ce->engine != engine)
>>> -				continue;
>>> +				goto next;
>>>    		}
>>> -		spin_lock_irqsave(&ce->guc_active.lock, flags);
>>> +		spin_lock(&ce->guc_active.lock);
>>>    		intel_engine_dump_active_requests(&ce->guc_active.requests,
>>>    						  hung_rq, m);
>>> -		spin_unlock_irqrestore(&ce->guc_active.lock, flags);
>>> +		spin_unlock(&ce->guc_active.lock);
>>> +
>>> +next:
>>> +		intel_context_put(ce);
>>> +		xa_lock(&guc->context_lookup);
>>>    	}
>>> +	xa_unlock_irqrestore(&guc->context_lookup, flags);
>>>    }
>>>    void intel_guc_submission_print_info(struct intel_guc *guc,
>>> @@ -2962,7 +3032,9 @@ void intel_guc_submission_print_context_info(struct intel_guc *guc,
>>>    {
>>>    	struct intel_context *ce;
>>>    	unsigned long index;
>>> +	unsigned long flags;
>>> +	xa_lock_irqsave(&guc->context_lookup, flags);
>>>    	xa_for_each(&guc->context_lookup, index, ce) {
>>>    		drm_printf(p, "GuC lrc descriptor %u:\n", ce->guc_id);
>>>    		drm_printf(p, "\tHW Context Desc: 0x%08x\n", ce->lrc.lrca);
>>> @@ -2981,6 +3053,7 @@ void intel_guc_submission_print_context_info(struct intel_guc *guc,
>>>    		guc_log_context_priority(p, ce);
>>>    	}
>>> +	xa_unlock_irqrestore(&guc->context_lookup, flags);
>>>    }
>>>    static struct intel_context *