[PATCH v3] drm/panthor: Fix UAF race between device unplug and FW event processing

[Ketil Johnsen <ketil.johnsen@arm.com>]

The function panthor_fw_unplug() will free the FW memory sections.
The problem is that there could still be pending FW events which are yet
not handled at this point. process_fw_events_work() can in this case try
to access said freed memory.

Simply call disable_work_sync() to both drain and prevent future
invocation of process_fw_events_work().

Signed-off-by: Ketil Johnsen <ketil.johnsen@arm.com>
Fixes: de85488138247 ("drm/panthor: Add the scheduler logical block")
---
v2:
- Followed Boris's advice and handle the race purely within the
  scheduler block (by adding a destroyed state)

v3:
- New approach, one single call to disable_work_sync()
---
 drivers/gpu/drm/panthor/panthor_sched.c | 1 +
 1 file changed, 1 insertion(+)

diff --git a/drivers/gpu/drm/panthor/panthor_sched.c b/drivers/gpu/drm/panthor/panthor_sched.c
index 0cc9055f4ee52..b7595beaa0205 100644
--- a/drivers/gpu/drm/panthor/panthor_sched.c
+++ b/drivers/gpu/drm/panthor/panthor_sched.c
@@ -3880,6 +3880,7 @@ void panthor_sched_unplug(struct panthor_device *ptdev)
 	struct panthor_scheduler *sched = ptdev->scheduler;
 
 	cancel_delayed_work_sync(&sched->tick_work);
+	disable_work_sync(&sched->fw_events_work);
 
 	mutex_lock(&sched->lock);
 	if (sched->pm.has_ref) {
-- 
2.47.2