On 30/10/2020 10:53, 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.

v2:
- Use atomic_cmpxchg() to conditionally schedule the reset work (Steven Privce)

Fixes: 1a11a88cfd9a ("drm/panfrost: Fix job timeout handling")
Cc: <sta...@vger.kernel.org>
Signed-off-by: Boris Brezillon <boris.brezil...@collabora.com>

LGTM!

Reviewed-by: Steven Price <steven.pr...@arm.com>

---
  drivers/gpu/drm/panfrost/panfrost_device.c |   1 -
  drivers/gpu/drm/panfrost/panfrost_device.h |   6 +-
  drivers/gpu/drm/panfrost/panfrost_job.c    | 127 ++++++++++++---------
  3 files changed, 79 insertions(+), 55 deletions(-)

diff --git a/drivers/gpu/drm/panfrost/panfrost_device.c 
b/drivers/gpu/drm/panfrost/panfrost_device.c
index ea8d31863c50..a83b2ff5837a 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 4902bc6624c8..14c11293791e 100644
--- a/drivers/gpu/drm/panfrost/panfrost_job.c
+++ b/drivers/gpu/drm/panfrost/panfrost_job.c
@@ -20,6 +20,8 @@
  #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))
@@ -382,19 +384,37 @@ static bool panfrost_scheduler_stop(struct panfrost_queue_state *queue,
                        drm_sched_increase_karma(bad);
                queue->stopped = true;
                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;
        }
        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);
+       /* Restore the original timeout before starting the scheduler. */
+       queue->sched.timeout = msecs_to_jiffies(JOB_TIMEOUT_MS);
+       drm_sched_start(&queue->sched, true);
+       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);
        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 +435,9 @@ 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_cmpxchg(&pfdev->reset.pending, 0, 1))
+               schedule_work(&pfdev->reset.work);
  }
static const struct drm_sched_backend_ops panfrost_sched_ops = {
@@ -531,11 +504,59 @@ 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;
+
+       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 to make sure the timer is not
+                * restarted after the cancellation.
+                */
+               pfdev->js->queue[i].sched.timeout = MAX_SCHEDULE_TIMEOUT;
+               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++) {
+               drm_sched_resubmit_jobs(&pfdev->js->queue[i].sched);
+               panfrost_scheduler_start(&pfdev->js->queue[i]);
+       }
+}
+
  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 +581,7 @@ 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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