Message-ID: <20250307155556.173494-1-ashley.smith@collabora.com>
Date: Fri,  7 Mar 2025 15:55:52 +0000
From: Ashley Smith <ashley.smith@...labora.com>
To: Boris Brezillon <boris.brezillon@...labora.com>,
	Steven Price <steven.price@....com>,
	Liviu Dudau <liviu.dudau@....com>,
	Maarten Lankhorst <maarten.lankhorst@...ux.intel.com>,
	Maxime Ripard <mripard@...nel.org>,
	Thomas Zimmermann <tzimmermann@...e.de>,
	David Airlie <airlied@...il.com>,
	Simona Vetter <simona@...ll.ch>,
	Heiko Stuebner <heiko@...ech.de>
Cc: kernel@...labora.com,
	Ashley Smith <ashley.smith@...labora.com>,
	Daniel Stone <daniels@...labora.com>,
	dri-devel@...ts.freedesktop.org,
	linux-kernel@...r.kernel.org
Subject: [PATCH] drm/panthor: Make the timeout per-queue instead of per-job

The timeout logic provided by drm_sched leads to races when we try
to suspend it while the drm_sched workqueue queues more jobs. Let's
overhaul the timeout handling in panthor to have our own delayed work
that's resumed/suspended when a group is resumed/suspended. When an
actual timeout occurs, we call drm_sched_fault() to report it
through drm_sched, still. But otherwise, the drm_sched timeout is
disabled (set to MAX_SCHEDULE_TIMEOUT), which leaves us in control of
how we protect modifications on the timer.

One issue seems to be when we call drm_sched_suspend_timeout() from
both queue_run_job() and tick_work() which could lead to races due to
drm_sched_suspend_timeout() not having a lock. Another issue seems to
be in queue_run_job() if the group is not scheduled, we suspend the
timeout again which undoes what drm_sched_job_begin() did when calling
drm_sched_start_timeout(). So the timeout does not reset when a job
is finished.

Co-developed-by: Boris Brezillon <boris.brezillon@...labora.com>
Signed-off-by: Boris Brezillon <boris.brezillon@...labora.com>
Tested-by: Daniel Stone <daniels@...labora.com>
Fixes: de8548813824 ("drm/panthor: Add the scheduler logical block")
Signed-off-by: Ashley Smith <ashley.smith@...labora.com>
---
 drivers/gpu/drm/panthor/panthor_sched.c | 233 +++++++++++++++++-------
 1 file changed, 167 insertions(+), 66 deletions(-)

diff --git a/drivers/gpu/drm/panthor/panthor_sched.c b/drivers/gpu/drm/panthor/panthor_sched.c
index 4d31d1967716..95eb5246c246 100644
--- a/drivers/gpu/drm/panthor/panthor_sched.c
+++ b/drivers/gpu/drm/panthor/panthor_sched.c
@@ -360,17 +360,20 @@ struct panthor_queue {
 	/** @entity: DRM scheduling entity used for this queue. */
 	struct drm_sched_entity entity;
 
-	/**
-	 * @remaining_time: Time remaining before the job timeout expires.
-	 *
-	 * The job timeout is suspended when the queue is not scheduled by the
-	 * FW. Every time we suspend the timer, we need to save the remaining
-	 * time so we can restore it later on.
-	 */
-	unsigned long remaining_time;
+	/** @timeout: Queue timeout related fields. */
+	struct {
+		/** @timeout.work: Work executed when a queue timeout occurs. */
+		struct delayed_work work;
 
-	/** @timeout_suspended: True if the job timeout was suspended. */
-	bool timeout_suspended;
+		/**
+		 * @remaining: Time remaining before a queue timeout.
+		 *
+		 * When the timer is running, this value is set to MAX_SCHEDULE_TIMEOUT.
+		 * When the timer is suspended, it's set to the time remaining when the
+		 * timer was suspended.
+		 */
+		unsigned long remaining;
+	} timeout;
 
 	/**
 	 * @doorbell_id: Doorbell assigned to this queue.
@@ -1031,6 +1034,82 @@ group_unbind_locked(struct panthor_group *group)
 	return 0;
 }
 
+static bool
+group_is_idle(struct panthor_group *group)
+{
+	struct panthor_device *ptdev = group->ptdev;
+	u32 inactive_queues;
+
+	if (group->csg_id >= 0)
+		return ptdev->scheduler->csg_slots[group->csg_id].idle;
+
+	inactive_queues = group->idle_queues | group->blocked_queues;
+	return hweight32(inactive_queues) == group->queue_count;
+}
+
+static void
+queue_suspend_timeout(struct panthor_queue *queue)
+{
+	unsigned long qtimeout, now;
+	struct panthor_group *group;
+	struct panthor_job *job;
+	bool timer_was_active;
+
+	spin_lock(&queue->fence_ctx.lock);
+
+	/* Already suspended, nothing to do. */
+	if (queue->timeout.remaining != MAX_SCHEDULE_TIMEOUT)
+		goto out_unlock;
+
+	job = list_first_entry_or_null(&queue->fence_ctx.in_flight_jobs,
+				       struct panthor_job, node);
+	group = job ? job->group : NULL;
+
+	/* If the queue is blocked and the group is idle, we want the timer to
+	 * keep running because the group can't be unblocked by other queues,
+	 * so it has to come from an external source, and we want to timebox
+	 * this external signalling.
+	 */
+	if (group && (group->blocked_queues & BIT(job->queue_idx)) &&
+	    group_is_idle(group))
+		goto out_unlock;
+
+	now = jiffies;
+	qtimeout = queue->timeout.work.timer.expires;
+
+	/* Cancel the timer. */
+	timer_was_active = cancel_delayed_work(&queue->timeout.work);
+	if (!timer_was_active || !job)
+		queue->timeout.remaining = msecs_to_jiffies(JOB_TIMEOUT_MS);
+	else if (time_after(qtimeout, now))
+		queue->timeout.remaining = qtimeout - now;
+	else
+		queue->timeout.remaining = 0;
+
+	if (WARN_ON_ONCE(queue->timeout.remaining > msecs_to_jiffies(JOB_TIMEOUT_MS)))
+		queue->timeout.remaining = msecs_to_jiffies(JOB_TIMEOUT_MS);
+
+out_unlock:
+	spin_unlock(&queue->fence_ctx.lock);
+}
+
+static void
+queue_resume_timeout(struct panthor_queue *queue)
+{
+	spin_lock(&queue->fence_ctx.lock);
+
+	/* When running, the remaining time is set to MAX_SCHEDULE_TIMEOUT. */
+	if (queue->timeout.remaining != MAX_SCHEDULE_TIMEOUT) {
+		mod_delayed_work(queue->scheduler.timeout_wq,
+				 &queue->timeout.work,
+				 queue->timeout.remaining);
+
+		queue->timeout.remaining = MAX_SCHEDULE_TIMEOUT;
+	}
+
+	spin_unlock(&queue->fence_ctx.lock);
+}
+
 /**
  * cs_slot_prog_locked() - Program a queue slot
  * @ptdev: Device.
@@ -1069,10 +1148,8 @@ cs_slot_prog_locked(struct panthor_device *ptdev, u32 csg_id, u32 cs_id)
 			       CS_IDLE_EMPTY |
 			       CS_STATE_MASK |
 			       CS_EXTRACT_EVENT);
-	if (queue->iface.input->insert != queue->iface.input->extract && queue->timeout_suspended) {
-		drm_sched_resume_timeout(&queue->scheduler, queue->remaining_time);
-		queue->timeout_suspended = false;
-	}
+	if (queue->iface.input->insert != queue->iface.input->extract)
+		queue_resume_timeout(queue);
 }
 
 /**
@@ -1099,14 +1176,7 @@ cs_slot_reset_locked(struct panthor_device *ptdev, u32 csg_id, u32 cs_id)
 			       CS_STATE_STOP,
 			       CS_STATE_MASK);
 
-	/* If the queue is blocked, we want to keep the timeout running, so
-	 * we can detect unbounded waits and kill the group when that happens.
-	 */
-	if (!(group->blocked_queues & BIT(cs_id)) && !queue->timeout_suspended) {
-		queue->remaining_time = drm_sched_suspend_timeout(&queue->scheduler);
-		queue->timeout_suspended = true;
-		WARN_ON(queue->remaining_time > msecs_to_jiffies(JOB_TIMEOUT_MS));
-	}
+	queue_suspend_timeout(queue);
 
 	return 0;
 }
@@ -1888,19 +1958,6 @@ tick_ctx_is_full(const struct panthor_scheduler *sched,
 	return ctx->group_count == sched->csg_slot_count;
 }
 
-static bool
-group_is_idle(struct panthor_group *group)
-{
-	struct panthor_device *ptdev = group->ptdev;
-	u32 inactive_queues;
-
-	if (group->csg_id >= 0)
-		return ptdev->scheduler->csg_slots[group->csg_id].idle;
-
-	inactive_queues = group->idle_queues | group->blocked_queues;
-	return hweight32(inactive_queues) == group->queue_count;
-}
-
 static bool
 group_can_run(struct panthor_group *group)
 {
@@ -2888,35 +2945,50 @@ void panthor_fdinfo_gather_group_samples(struct panthor_file *pfile)
 	xa_unlock(&gpool->xa);
 }
 
-static void group_sync_upd_work(struct work_struct *work)
+static bool queue_check_job_completion(struct panthor_queue *queue)
 {
-	struct panthor_group *group =
-		container_of(work, struct panthor_group, sync_upd_work);
+	struct panthor_syncobj_64b *syncobj = NULL;
 	struct panthor_job *job, *job_tmp;
+	bool cookie, progress = false;
 	LIST_HEAD(done_jobs);
-	u32 queue_idx;
-	bool cookie;
 
 	cookie = dma_fence_begin_signalling();
-	for (queue_idx = 0; queue_idx < group->queue_count; queue_idx++) {
-		struct panthor_queue *queue = group->queues[queue_idx];
-		struct panthor_syncobj_64b *syncobj;
+	spin_lock(&queue->fence_ctx.lock);
+	list_for_each_entry_safe(job, job_tmp, &queue->fence_ctx.in_flight_jobs, node) {
+		if (!syncobj) {
+			struct panthor_group *group = job->group;
 
-		if (!queue)
-			continue;
+			syncobj = group->syncobjs->kmap +
+				  (job->queue_idx * sizeof(*syncobj));
+		}
 
-		syncobj = group->syncobjs->kmap + (queue_idx * sizeof(*syncobj));
+		if (syncobj->seqno < job->done_fence->seqno)
+			break;
 
-		spin_lock(&queue->fence_ctx.lock);
-		list_for_each_entry_safe(job, job_tmp, &queue->fence_ctx.in_flight_jobs, node) {
-			if (syncobj->seqno < job->done_fence->seqno)
-				break;
+		list_move_tail(&job->node, &done_jobs);
+		dma_fence_signal_locked(job->done_fence);
+	}
 
-			list_move_tail(&job->node, &done_jobs);
-			dma_fence_signal_locked(job->done_fence);
-		}
-		spin_unlock(&queue->fence_ctx.lock);
+	if (list_empty(&queue->fence_ctx.in_flight_jobs)) {
+		/* If we have no job left, we cancel the timer, and reset remaining
+		 * time to its default so it can be restarted next time
+		 * queue_resume_timeout() is called.
+		 */
+		cancel_delayed_work(&queue->timeout.work);
+		queue->timeout.remaining = msecs_to_jiffies(JOB_TIMEOUT_MS);
+
+		/* If there's no job pending, we consider it progress to avoid a
+		 * spurious timeout if the timeout handler and the sync update
+		 * handler raced.
+		 */
+		progress = true;
+	} else if (!list_empty(&done_jobs)) {
+		mod_delayed_work(queue->scheduler.timeout_wq,
+				 &queue->timeout.work,
+				 msecs_to_jiffies(JOB_TIMEOUT_MS));
+		progress = true;
 	}
+	spin_unlock(&queue->fence_ctx.lock);
 	dma_fence_end_signalling(cookie);
 
 	list_for_each_entry_safe(job, job_tmp, &done_jobs, node) {
@@ -2926,6 +2998,27 @@ static void group_sync_upd_work(struct work_struct *work)
 		panthor_job_put(&job->base);
 	}
 
+	return progress;
+}
+
+static void group_sync_upd_work(struct work_struct *work)
+{
+	struct panthor_group *group =
+		container_of(work, struct panthor_group, sync_upd_work);
+	u32 queue_idx;
+	bool cookie;
+
+	cookie = dma_fence_begin_signalling();
+	for (queue_idx = 0; queue_idx < group->queue_count; queue_idx++) {
+		struct panthor_queue *queue = group->queues[queue_idx];
+
+		if (!queue)
+			continue;
+
+		queue_check_job_completion(queue);
+	}
+	dma_fence_end_signalling(cookie);
+
 	group_put(group);
 }
 
@@ -3173,17 +3266,6 @@ queue_run_job(struct drm_sched_job *sched_job)
 	queue->iface.input->insert = job->ringbuf.end;
 
 	if (group->csg_id < 0) {
-		/* If the queue is blocked, we want to keep the timeout running, so we
-		 * can detect unbounded waits and kill the group when that happens.
-		 * Otherwise, we suspend the timeout so the time we spend waiting for
-		 * a CSG slot is not counted.
-		 */
-		if (!(group->blocked_queues & BIT(job->queue_idx)) &&
-		    !queue->timeout_suspended) {
-			queue->remaining_time = drm_sched_suspend_timeout(&queue->scheduler);
-			queue->timeout_suspended = true;
-		}
-
 		group_schedule_locked(group, BIT(job->queue_idx));
 	} else {
 		gpu_write(ptdev, CSF_DOORBELL(queue->doorbell_id), 1);
@@ -3192,6 +3274,7 @@ queue_run_job(struct drm_sched_job *sched_job)
 			pm_runtime_get(ptdev->base.dev);
 			sched->pm.has_ref = true;
 		}
+		queue_resume_timeout(queue);
 		panthor_devfreq_record_busy(sched->ptdev);
 	}
 
@@ -3241,6 +3324,11 @@ queue_timedout_job(struct drm_sched_job *sched_job)
 
 	queue_start(queue);
 
+	/* We already flagged the queue as faulty, make sure we don't get
+	 * called again.
+	 */
+	queue->scheduler.timeout = MAX_SCHEDULE_TIMEOUT;
+
 	return DRM_GPU_SCHED_STAT_NOMINAL;
 }
 
@@ -3283,6 +3371,17 @@ static u32 calc_profiling_ringbuf_num_slots(struct panthor_device *ptdev,
 	return DIV_ROUND_UP(cs_ringbuf_size, min_profiled_job_instrs * sizeof(u64));
 }
 
+static void queue_timeout_work(struct work_struct *work)
+{
+	struct panthor_queue *queue = container_of(work, struct panthor_queue,
+						   timeout.work.work);
+	bool progress;
+
+	progress = queue_check_job_completion(queue);
+	if (!progress)
+		drm_sched_fault(&queue->scheduler);
+}
+
 static struct panthor_queue *
 group_create_queue(struct panthor_group *group,
 		   const struct drm_panthor_queue_create *args)
@@ -3298,7 +3397,7 @@ group_create_queue(struct panthor_group *group,
 		 * their profiling status.
 		 */
 		.credit_limit = args->ringbuf_size / sizeof(u64),
-		.timeout = msecs_to_jiffies(JOB_TIMEOUT_MS),
+		.timeout = MAX_SCHEDULE_TIMEOUT,
 		.timeout_wq = group->ptdev->reset.wq,
 		.name = "panthor-queue",
 		.dev = group->ptdev->base.dev,
@@ -3321,6 +3420,8 @@ group_create_queue(struct panthor_group *group,
 	if (!queue)
 		return ERR_PTR(-ENOMEM);
 
+	queue->timeout.remaining = msecs_to_jiffies(JOB_TIMEOUT_MS);
+	INIT_DELAYED_WORK(&queue->timeout.work, queue_timeout_work);
 	queue->fence_ctx.id = dma_fence_context_alloc(1);
 	spin_lock_init(&queue->fence_ctx.lock);
 	INIT_LIST_HEAD(&queue->fence_ctx.in_flight_jobs);

base-commit: b72f66f22c0e39ae6684c43fead774c13db24e73
-- 
2.43.0

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