[PATCH v8 02/12] accel/rocket: wait for a running IRQ handler before resetting a core

[Jiaxing Hu]

rocket_reset() calls drm_sched_stop(), which stops the scheduler and
returns. It does not wait for a threaded handler that is already
running, so the comment that follows, "Remaining interrupts have been
handled", states an assumption rather than something the code arranges.

Call synchronize_irq(core->irq) after drm_sched_stop() and reword the
comment to say what holds afterwards.

It has to go before the scoped_guard(mutex, &core->job_lock) rather than
inside it. rocket_job_handle_irq() takes job_lock, so waiting for the
handler while holding that lock would be waiting for a handler that is
waiting for us. Nothing is held at that point, and both callers,
rocket_job_timedout() and rocket_reset_work(), run in process context,
so sleeping there is allowed.

This does not stop a handler that has already read in_flight_job from
finishing its work on the job the reset is about to drop. That window
needs the check and the register writes to be one step under the lock,
which is what the previous patch does; the two are complementary.

Suggested-by: Igor Paunovic <royalnet026 at gmail.com>
Signed-off-by: Jiaxing Hu <gahing at gahingwoo.com>
---
 drivers/accel/rocket/rocket_job.c | 14 +++++++++++---
 1 file changed, 11 insertions(+), 3 deletions(-)

diff --git a/drivers/accel/rocket/rocket_job.c b/drivers/accel/rocket/rocket_job.c
index 5f0f9682e..d484a3a6f 100644
--- a/drivers/accel/rocket/rocket_job.c
+++ b/drivers/accel/rocket/rocket_job.c
@@ -377,9 +377,17 @@ rocket_reset(struct rocket_core *core, struct drm_sched_job *bad)
 	drm_sched_stop(&core->sched, bad);
 
 	/*
-	 * Remaining interrupts have been handled, but we might still have
-	 * stuck jobs. Let's make sure the PM counters stay balanced by
-	 * manually calling pm_runtime_put_noidle().
+	 * drm_sched_stop() returns without waiting for a threaded handler that
+	 * is already running, so wait for one here. This has to stay outside
+	 * job_lock: the handler takes that lock, so waiting for it while
+	 * holding it would deadlock instead of fencing anything.
+	 */
+	synchronize_irq(core->irq);
+
+	/*
+	 * No handler is running now, but we might still have stuck jobs. Let's
+	 * make sure the PM counters stay balanced by manually calling
+	 * pm_runtime_put_noidle().
 	 */
 	scoped_guard(mutex, &core->job_lock) {
 		if (core->in_flight_job)
-- 
2.43.0