In our last attempt to fix races in the panfrost_job_timedout() path we
overlooked the case where a re-submitted job immediately triggers a
fault. This lead to a situation where we try to stop a scheduler that's
not resumed yet and lose the 'timedout' event without restarting the
timeout, thus blocking the whole queue.
Let's fix that by tracking timeouts occurring between the
drm_sched_resubmit_jobs() and drm_sched_start() calls.
v2:
- Fix another race (reported by Steven)
Fixes: 1a11a88cfd9a ("drm/panfrost: Fix job timeout handling")
Cc: <stable@xxxxxxxxxxxxxxx>
Signed-off-by: Boris Brezillon <boris.brezillon@xxxxxxxxxxxxx>
---
drivers/gpu/drm/panfrost/panfrost_job.c | 61 +++++++++++++++++--------
1 file changed, 43 insertions(+), 18 deletions(-)
diff --git a/drivers/gpu/drm/panfrost/panfrost_job.c b/drivers/gpu/drm/panfrost/panfrost_job.c
index d0469e944143..0f9a34f5c6d0 100644
--- a/drivers/gpu/drm/panfrost/panfrost_job.c
+++ b/drivers/gpu/drm/panfrost/panfrost_job.c
@@ -26,6 +26,7 @@
struct panfrost_queue_state {
struct drm_gpu_scheduler sched;
bool stopped;
+ bool timedout;
struct mutex lock;
u64 fence_context;
u64 emit_seqno;
@@ -383,11 +384,33 @@ static bool panfrost_scheduler_stop(struct panfrost_queue_state *queue,
queue->stopped = true;
stopped = true;
}
+ queue->timedout = true;
mutex_unlock(&queue->lock);
return stopped;
}
+static void panfrost_scheduler_start(struct panfrost_queue_state *queue)
+{
+ if (WARN_ON(!queue->stopped))
+ return;
+
+ mutex_lock(&queue->lock);
+ drm_sched_start(&queue->sched, true);
+
+ /*
+ * We might have missed fault-timeouts (AKA immediate timeouts) while
+ * the scheduler was stopped. Let's fake a new fault to trigger an
+ * immediate reset.
+ */
+ if (queue->timedout)
+ drm_sched_fault(&queue->sched);
+
+ queue->timedout = false;
+ queue->stopped = false;
+ mutex_unlock(&queue->lock);
+}
+
static void panfrost_job_timedout(struct drm_sched_job *sched_job)
{
struct panfrost_job *job = to_panfrost_job(sched_job);
@@ -422,27 +445,20 @@ static void panfrost_job_timedout(struct drm_sched_job *sched_job)
struct drm_gpu_scheduler *sched = &pfdev->js->queue[i].sched;
/*
- * If the queue is still active, make sure we wait for any
- * pending timeouts.
+ * Stop the scheduler and wait for any pending timeout handler
+ * to return.
*/
- if (!pfdev->js->queue[i].stopped)
+ panfrost_scheduler_stop(&pfdev->js->queue[i], NULL);
+ if (i != js)
cancel_delayed_work_sync(&sched->work_tdr);
/*
- * If the scheduler was not already stopped, there's a tiny
- * chance a timeout has expired just before we stopped it, and
- * drm_sched_stop() does not flush pending works. Let's flush
- * them now so the timeout handler doesn't get called in the
- * middle of a reset.
+ * We do another stop after cancel_delayed_work_sync() to make
+ * sure we don't race against another thread finishing its
+ * reset (the restart queue steps are not protected by the
+ * reset lock).
*/
- if (panfrost_scheduler_stop(&pfdev->js->queue[i], NULL))
- cancel_delayed_work_sync(&sched->work_tdr);
-
- /*
- * Now that we cancelled the pending timeouts, we can safely
- * reset the stopped state.
- */
- pfdev->js->queue[i].stopped = false;
+ panfrost_scheduler_stop(&pfdev->js->queue[i], NULL);
}
spin_lock_irqsave(&pfdev->js->job_lock, flags);
@@ -457,14 +473,23 @@ static void panfrost_job_timedout(struct drm_sched_job *sched_job)
panfrost_device_reset(pfdev);
- for (i = 0; i < NUM_JOB_SLOTS; i++)
+ for (i = 0; i < NUM_JOB_SLOTS; i++) {
+ /*
+ * The GPU is idle, and the scheduler is stopped, we can safely
+ * reset the ->timedout state without taking any lock. We need
+ * to do that before calling drm_sched_resubmit_jobs() though,
+ * because the resubmission might trigger immediate faults
+ * which we want to catch.
+ */
+ pfdev->js->queue[i].timedout = false;
drm_sched_resubmit_jobs(&pfdev->js->queue[i].sched);
+ }
mutex_unlock(&pfdev->reset_lock);
/* restart scheduler after GPU is usable again */
for (i = 0; i < NUM_JOB_SLOTS; i++)
- drm_sched_start(&pfdev->js->queue[i].sched, true);
+ panfrost_scheduler_start(&pfdev->js->queue[i]);
}
static const struct drm_sched_backend_ops panfrost_sched_ops = {
--
2.26.2
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