A flaw in the Linux Kernel found in drivers/media/dvb-core/dvb_frontend.c. There is a blocking operation when a task is in !TASK_RUNNING. In dvb_frontend_get_event, wait_event_interruptible is called; the condition is dvb_frontend_test_event(fepriv,events). In dvb_frontend_test_event, down(&fepriv->sem) is called. However, wait_event_interruptible would put the process to sleep, and down(&fepriv->sem) may block the process.

Reference:
https://lore.kernel.org/all/CA+UBctCu7fXn4q41O_3=id1+OdyQ85tZY1x+TkT-6OVBL6KAUw@mail.gmail.com/