io_uring: allow IO worker threads to be frozen

With the freezer using the proper signaling to notify us of when it's
time to freeze a thread, we can re-enable normal freezer usage for the
IO threads. Ensure that SQPOLL, io-wq, and the io-wq manager call
try_to_freeze() appropriately, and remove the default setting of
PF_NOFREEZE from create_io_thread().
Signed-off-by: Jens Axboe <axboe@kernel.dk>

fs/io-wq.c

@@ -488,6 +488,8 @@ static int io_wqe_worker(void *data)
 	set_task_comm(current, buf);
 
 	while (!test_bit(IO_WQ_BIT_EXIT, &wq->state)) {
+		long ret;
+
 		set_current_state(TASK_INTERRUPTIBLE);
 loop:
 		raw_spin_lock_irq(&wqe->lock);
@@ -498,7 +500,8 @@ static int io_wqe_worker(void *data)
 		__io_worker_idle(wqe, worker);
 		raw_spin_unlock_irq(&wqe->lock);
 		io_flush_signals();
-		if (schedule_timeout(WORKER_IDLE_TIMEOUT))
+		ret = schedule_timeout(WORKER_IDLE_TIMEOUT);
+		if (try_to_freeze() || ret)
 			continue;
 		if (fatal_signal_pending(current))
 			break;
@@ -709,6 +712,7 @@ static int io_wq_manager(void *data)
 		set_current_state(TASK_INTERRUPTIBLE);
 		io_wq_check_workers(wq);
 		schedule_timeout(HZ);
+		try_to_freeze();
 		if (fatal_signal_pending(current))
 			set_bit(IO_WQ_BIT_EXIT, &wq->state);
 	} while (!test_bit(IO_WQ_BIT_EXIT, &wq->state));

fs/io_uring.c

@@ -6752,6 +6752,7 @@ static int io_sq_thread(void *data)
 
 			up_read(&sqd->rw_lock);
 			schedule();
+			try_to_freeze();
 			down_read(&sqd->rw_lock);
 			list_for_each_entry(ctx, &sqd->ctx_list, sqd_list)
 				io_ring_clear_wakeup_flag(ctx);

kernel/fork.c

@@ -2436,7 +2436,6 @@ struct task_struct *create_io_thread(int (*fn)(void *), void *arg, int node)
 	if (!IS_ERR(tsk)) {
 		sigfillset(&tsk->blocked);
 		sigdelsetmask(&tsk->blocked, sigmask(SIGKILL));
-		tsk->flags |= PF_NOFREEZE;
 	}
 	return tsk;
 }