io_uring/io-wq: handle !sysctl_hung_task_timeout_secs

If the hung_task_timeout sysctl is set to 0, then we'll end up busy
looping inside io_wq_exit_workers() after an earlier commit switched to
using wait_for_completion_timeout(). Use the maximum schedule timeout
value for that case.

Fixes: 1f29309 ("io_uring/io-wq: don't trigger hung task for syzbot craziness")
Reported-by: Chris Mason <clm@fb.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>

Author: axboe

io_uring/io-wq.c

@@ -1340,6 +1340,8 @@ static void io_wq_exit_workers(struct io_wq *wq)
 	 * up waiting more than IO_URING_EXIT_WAIT_MAX.
 	 */
 	timeout = sysctl_hung_task_timeout_secs * HZ / 2;
+	if (!timeout)
+		timeout = MAX_SCHEDULE_TIMEOUT;
 	warn_timeout = jiffies + IO_URING_EXIT_WAIT_MAX;
 	do {
 		if (wait_for_completion_timeout(&wq->worker_done, timeout))