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@vger.kernel.org Signed-off-by: Boris Brezillon boris.brezillon@collabora.com --- 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 = {