[PATCH v4] drm/panfrost: Move the GPU reset bits outside the timeout handler
Steven Price
steven.price at arm.com
Thu Nov 5 13:27:04 UTC 2020
On 04/11/2020 17:07, Boris Brezillon wrote:
> We've fixed many races in panfrost_job_timedout() but some remain.
> Instead of trying to fix it again, let's simplify the logic and move
> the reset bits to a separate work scheduled when one of the queue
> reports a timeout.
>
> v4:
> - Rework the logic to prevent a race between drm_sched_start()
> (reset work) and drm_sched_job_timedout() (timeout work)
> - Drop Steven's R-b
> - Add dma_fence annotation to the panfrost_reset() function (Daniel Vetter)
>
> v3:
> - Replace the atomic_cmpxchg() by an atomic_xchg() (Robin Murphy)
> - Add Steven's R-b
>
> v2:
> - Use atomic_cmpxchg() to conditionally schedule the reset work (Steven Price)
>
> Fixes: 1a11a88cfd9a ("drm/panfrost: Fix job timeout handling")
> Cc: <stable at vger.kernel.org>
> Signed-off-by: Boris Brezillon <boris.brezillon at collabora.com>
Hi Boris,
A couple of nits below, but otherwise looks good.
> ---
> drivers/gpu/drm/panfrost/panfrost_device.c | 1 -
> drivers/gpu/drm/panfrost/panfrost_device.h | 6 +-
> drivers/gpu/drm/panfrost/panfrost_job.c | 190 ++++++++++++++-------
> 3 files changed, 133 insertions(+), 64 deletions(-)
>
> diff --git a/drivers/gpu/drm/panfrost/panfrost_device.c b/drivers/gpu/drm/panfrost/panfrost_device.c
> index 1daf9322954a..fbcf5edbe367 100644
> --- a/drivers/gpu/drm/panfrost/panfrost_device.c
> +++ b/drivers/gpu/drm/panfrost/panfrost_device.c
> @@ -200,7 +200,6 @@ int panfrost_device_init(struct panfrost_device *pfdev)
> struct resource *res;
>
> mutex_init(&pfdev->sched_lock);
> - mutex_init(&pfdev->reset_lock);
> INIT_LIST_HEAD(&pfdev->scheduled_jobs);
> INIT_LIST_HEAD(&pfdev->as_lru_list);
>
> diff --git a/drivers/gpu/drm/panfrost/panfrost_device.h b/drivers/gpu/drm/panfrost/panfrost_device.h
> index 140e004a3790..597cf1459b0a 100644
> --- a/drivers/gpu/drm/panfrost/panfrost_device.h
> +++ b/drivers/gpu/drm/panfrost/panfrost_device.h
> @@ -106,7 +106,11 @@ struct panfrost_device {
> struct panfrost_perfcnt *perfcnt;
>
> struct mutex sched_lock;
> - struct mutex reset_lock;
> +
> + struct {
> + struct work_struct work;
> + atomic_t pending;
> + } reset;
>
> struct mutex shrinker_lock;
> struct list_head shrinker_list;
> diff --git a/drivers/gpu/drm/panfrost/panfrost_job.c b/drivers/gpu/drm/panfrost/panfrost_job.c
> index e75b7d2192f7..643d26854b46 100644
> --- a/drivers/gpu/drm/panfrost/panfrost_job.c
> +++ b/drivers/gpu/drm/panfrost/panfrost_job.c
> @@ -20,12 +20,21 @@
> #include "panfrost_gpu.h"
> #include "panfrost_mmu.h"
>
> +#define JOB_TIMEOUT_MS 500
> +
> #define job_write(dev, reg, data) writel(data, dev->iomem + (reg))
> #define job_read(dev, reg) readl(dev->iomem + (reg))
>
> +enum panfrost_queue_status {
> + PANFROST_QUEUE_STATUS_ACTIVE,
> + PANFROST_QUEUE_STATUS_STOPPED,
> + PANFROST_QUEUE_STATUS_STARTING,
> + PANFROST_QUEUE_STATUS_FAULT_PENDING,
> +};
> +
> struct panfrost_queue_state {
> struct drm_gpu_scheduler sched;
> - bool stopped;
> + atomic_t status;
> struct mutex lock;
> u64 fence_context;
> u64 emit_seqno;
> @@ -373,28 +382,64 @@ void panfrost_job_enable_interrupts(struct panfrost_device *pfdev)
> static bool panfrost_scheduler_stop(struct panfrost_queue_state *queue,
> struct drm_sched_job *bad)
> {
> + enum panfrost_queue_status old_status;
> bool stopped = false;
>
> mutex_lock(&queue->lock);
> - if (!queue->stopped) {
> - drm_sched_stop(&queue->sched, bad);
> - if (bad)
> - drm_sched_increase_karma(bad);
> - queue->stopped = true;
> - stopped = true;
> - }
> + old_status = atomic_xchg(&queue->status,
> + PANFROST_QUEUE_STATUS_STOPPED);
> + WARN_ON(old_status != PANFROST_QUEUE_STATUS_ACTIVE &&
> + old_status != PANFROST_QUEUE_STATUS_STOPPED);
> + if (old_status == PANFROST_QUEUE_STATUS_STOPPED)
> + goto out;
NIT: It's slightly cleaner if you swap the above lines, i.e.:
if (old_status == PANFROST_QUEUE_STATUS_STOPPED)
goto out;
WARN_ON(old_status != PANFROST_QUEUE_STATUS_ACTIVE);
> +
> + drm_sched_stop(&queue->sched, bad);
> + if (bad)
> + drm_sched_increase_karma(bad);
> +
> + stopped = true;
> +
> + /*
> + * Set the timeout to max so the timer doesn't get started
> + * when we return from the timeout handler (restored in
> + * panfrost_scheduler_start()).
> + */
> + queue->sched.timeout = MAX_SCHEDULE_TIMEOUT;
> +
> +out:
> mutex_unlock(&queue->lock);
>
> return stopped;
> }
>
> +static void panfrost_scheduler_start(struct panfrost_queue_state *queue)
> +{
> + enum panfrost_queue_status old_status;
> +
> + mutex_lock(&queue->lock);
> + old_status = atomic_xchg(&queue->status,
> + PANFROST_QUEUE_STATUS_STARTING);
> + if (WARN_ON(old_status != PANFROST_QUEUE_STATUS_STOPPED))
> + goto out;
The error handling isn't great here - in this case the queue status is
left in _STATUS_STARTING, which at best would lead to another WARN_ON
being hit, but also has the effect of ignoring job faults. Probably the
timeout would eventually get things back to normal.
Obviously this situation will never occur™, but we can do better either
by continuing with the normal logic below, or even better replacing
atomic_xchg() with an atomic_cmpxchg() (so leave the status alone if not
_STOPPED). Both seem like better error recovery options to me. But keep
the WARN_ON because something has clearly gone wrong if this happens.
Thanks,
Steve
> +
> + /* Restore the original timeout before starting the scheduler. */
> + queue->sched.timeout = msecs_to_jiffies(JOB_TIMEOUT_MS);
> + drm_sched_resubmit_jobs(&queue->sched);
> + drm_sched_start(&queue->sched, true);
> + old_status = atomic_xchg(&queue->status,
> + PANFROST_QUEUE_STATUS_ACTIVE);
> + if (old_status == PANFROST_QUEUE_STATUS_FAULT_PENDING)
> + drm_sched_fault(&queue->sched);
> +
> +out:
> + mutex_unlock(&queue->lock);
> +}
> +
> static void panfrost_job_timedout(struct drm_sched_job *sched_job)
> {
> struct panfrost_job *job = to_panfrost_job(sched_job);
> struct panfrost_device *pfdev = job->pfdev;
> int js = panfrost_job_get_slot(job);
> - unsigned long flags;
> - int i;
>
> /*
> * If the GPU managed to complete this jobs fence, the timeout is
> @@ -415,56 +460,9 @@ static void panfrost_job_timedout(struct drm_sched_job *sched_job)
> if (!panfrost_scheduler_stop(&pfdev->js->queue[js], sched_job))
> return;
>
> - if (!mutex_trylock(&pfdev->reset_lock))
> - return;
> -
> - for (i = 0; i < NUM_JOB_SLOTS; i++) {
> - struct drm_gpu_scheduler *sched = &pfdev->js->queue[i].sched;
> -
> - /*
> - * If the queue is still active, make sure we wait for any
> - * pending timeouts.
> - */
> - if (!pfdev->js->queue[i].stopped)
> - 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.
> - */
> - 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;
> - }
> -
> - spin_lock_irqsave(&pfdev->js->job_lock, flags);
> - for (i = 0; i < NUM_JOB_SLOTS; i++) {
> - if (pfdev->jobs[i]) {
> - pm_runtime_put_noidle(pfdev->dev);
> - panfrost_devfreq_record_idle(&pfdev->pfdevfreq);
> - pfdev->jobs[i] = NULL;
> - }
> - }
> - spin_unlock_irqrestore(&pfdev->js->job_lock, flags);
> -
> - panfrost_device_reset(pfdev);
> -
> - for (i = 0; i < NUM_JOB_SLOTS; i++)
> - 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);
> + /* Schedule a reset if there's no reset in progress. */
> + if (!atomic_xchg(&pfdev->reset.pending, 1))
> + schedule_work(&pfdev->reset.work);
> }
>
> static const struct drm_sched_backend_ops panfrost_sched_ops = {
> @@ -496,6 +494,8 @@ static irqreturn_t panfrost_job_irq_handler(int irq, void *data)
> job_write(pfdev, JOB_INT_CLEAR, mask);
>
> if (status & JOB_INT_MASK_ERR(j)) {
> + enum panfrost_queue_status old_status;
> +
> job_write(pfdev, JS_COMMAND_NEXT(j), JS_COMMAND_NOP);
>
> dev_err(pfdev->dev, "js fault, js=%d, status=%s, head=0x%x, tail=0x%x",
> @@ -504,7 +504,18 @@ static irqreturn_t panfrost_job_irq_handler(int irq, void *data)
> job_read(pfdev, JS_HEAD_LO(j)),
> job_read(pfdev, JS_TAIL_LO(j)));
>
> - drm_sched_fault(&pfdev->js->queue[j].sched);
> + /*
> + * When the queue is being restarted we don't report
> + * faults directly to avoid races between the timeout
> + * and reset handlers. panfrost_scheduler_start() will
> + * call drm_sched_fault() after the queue has been
> + * started if status == FAULT_PENDING.
> + */
> + old_status = atomic_cmpxchg(&pfdev->js->queue[j].status,
> + PANFROST_QUEUE_STATUS_STARTING,
> + PANFROST_QUEUE_STATUS_FAULT_PENDING);
> + if (old_status == PANFROST_QUEUE_STATUS_ACTIVE)
> + drm_sched_fault(&pfdev->js->queue[j].sched);
> }
>
> if (status & JOB_INT_MASK_DONE(j)) {
> @@ -531,11 +542,66 @@ static irqreturn_t panfrost_job_irq_handler(int irq, void *data)
> return IRQ_HANDLED;
> }
>
> +static void panfrost_reset(struct work_struct *work)
> +{
> + struct panfrost_device *pfdev = container_of(work,
> + struct panfrost_device,
> + reset.work);
> + unsigned long flags;
> + unsigned int i;
> + bool cookie;
> +
> + cookie = dma_fence_begin_signalling();
> + for (i = 0; i < NUM_JOB_SLOTS; i++) {
> + /*
> + * We want pending timeouts to be handled before we attempt
> + * to stop the scheduler. If we don't do that and the timeout
> + * handler is in flight, it might have removed the bad job
> + * from the list, and we'll lose this job if the reset handler
> + * enters the critical section in panfrost_scheduler_stop()
> + * before the timeout handler.
> + *
> + * Timeout is set to MAX_SCHEDULE_TIMEOUT - 1 because we need
> + * something big enough to make sure the timer will not expire
> + * before we manage to stop the scheduler, but we can't use
> + * MAX_SCHEDULE_TIMEOUT because drm_sched_get_cleanup_job()
> + * considers that as 'timer is not running' and will dequeue
> + * the job without making sure the timeout handler is not
> + * running.
> + */
> + pfdev->js->queue[i].sched.timeout = MAX_SCHEDULE_TIMEOUT - 1;
> + cancel_delayed_work_sync(&pfdev->js->queue[i].sched.work_tdr);
> + panfrost_scheduler_stop(&pfdev->js->queue[i], NULL);
> + }
> +
> + /* All timers have been stopped, we can safely reset the pending state. */
> + atomic_set(&pfdev->reset.pending, 0);
> +
> + spin_lock_irqsave(&pfdev->js->job_lock, flags);
> + for (i = 0; i < NUM_JOB_SLOTS; i++) {
> + if (pfdev->jobs[i]) {
> + pm_runtime_put_noidle(pfdev->dev);
> + panfrost_devfreq_record_idle(&pfdev->pfdevfreq);
> + pfdev->jobs[i] = NULL;
> + }
> + }
> + spin_unlock_irqrestore(&pfdev->js->job_lock, flags);
> +
> + panfrost_device_reset(pfdev);
> +
> + for (i = 0; i < NUM_JOB_SLOTS; i++)
> + panfrost_scheduler_start(&pfdev->js->queue[i]);
> +
> + dma_fence_end_signalling(cookie);
> +}
> +
> int panfrost_job_init(struct panfrost_device *pfdev)
> {
> struct panfrost_job_slot *js;
> int ret, j, irq;
>
> + INIT_WORK(&pfdev->reset.work, panfrost_reset);
> +
> pfdev->js = js = devm_kzalloc(pfdev->dev, sizeof(*js), GFP_KERNEL);
> if (!js)
> return -ENOMEM;
> @@ -560,7 +626,7 @@ int panfrost_job_init(struct panfrost_device *pfdev)
>
> ret = drm_sched_init(&js->queue[j].sched,
> &panfrost_sched_ops,
> - 1, 0, msecs_to_jiffies(500),
> + 1, 0, msecs_to_jiffies(JOB_TIMEOUT_MS),
> "pan_js");
> if (ret) {
> dev_err(pfdev->dev, "Failed to create scheduler: %d.", ret);
>
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