drm/panfrost: Handle resetting on timeout better

Panfrost uses multiple schedulers (one for each slot, so 2 in reality),
and on a timeout has to stop all the schedulers to safely perform a
reset. However more than one scheduler can trigger a timeout at the same
time. This race condition results in jobs being freed while they are
still in use.

When stopping other slots use cancel_delayed_work_sync() to ensure that
any timeout started for that slot has completed. Also use
mutex_trylock() to obtain reset_lock. This means that only one thread
attempts the reset, the other threads will simply complete without doing
anything (the first thread will wait for this in the call to
cancel_delayed_work_sync()).

While we're here and since the function is already dependent on
sched_job not being NULL, let's remove the unnecessary checks.

Fixes: aa20236784ab ("drm/panfrost: Prevent concurrent resets")
Tested-by: Neil Armstrong <narmstrong@baylibre.com>
Signed-off-by: Steven Price <steven.price@arm.com>
Signed-off-by: Rob Herring <robh@kernel.org>
Link: https://patchwork.freedesktop.org/patch/msgid/20191009094456.9704-1-steven.price@arm.com

diff --git a/drivers/gpu/drm/panfrost/panfrost_job.c b/drivers/gpu/drm/panfrost/panfrost_job.c
index a585516..21f34d4 100644 (file)
--- a/drivers/gpu/drm/panfrost/panfrost_job.c
+++ b/drivers/gpu/drm/panfrost/panfrost_job.c
@@ -381,13 +381,19 @@ static void panfrost_job_timedout(struct drm_sched_job *sched_job)
                job_read(pfdev, JS_TAIL_LO(js)),
                sched_job);
 
-       mutex_lock(&pfdev->reset_lock);
+       if (!mutex_trylock(&pfdev->reset_lock))
+               return;
 
-       for (i = 0; i < NUM_JOB_SLOTS; i++)
-               drm_sched_stop(&pfdev->js->queue[i].sched, sched_job);
+       for (i = 0; i < NUM_JOB_SLOTS; i++) {
+               struct drm_gpu_scheduler *sched = &pfdev->js->queue[i].sched;
+
+               drm_sched_stop(sched, sched_job);
+               if (js != i)
+                       /* Ensure any timeouts on other slots have finished */
+                       cancel_delayed_work_sync(&sched->work_tdr);
+       }
 
-       if (sched_job)
-               drm_sched_increase_karma(sched_job);
+       drm_sched_increase_karma(sched_job);
 
        spin_lock_irqsave(&pfdev->js->job_lock, flags);
        for (i = 0; i < NUM_JOB_SLOTS; i++) {