io_uring: fix false WARN_ONCE

WARNING: CPU: 1 PID: 11749 at fs/io-wq.c:244 io_wqe_wake_worker fs/io-wq.c:244 [inline]
WARNING: CPU: 1 PID: 11749 at fs/io-wq.c:244 io_wqe_enqueue+0x7f6/0x910 fs/io-wq.c:751

A WARN_ON_ONCE() in io_wqe_wake_worker() can be triggered by a valid
userspace setup. Replace it with pr_warn.

Reported-by: syzbot+ea2f1484cffe5109dc10@syzkaller.appspotmail.com
Signed-off-by: Pavel Begunkov <asml.silence@gmail.com>
Link: https://lore.kernel.org/r/f7ede342c3342c4c26668f5168e2993e38bbd99c.1623949695.git.asml.silence@gmail.comSigned-off-by: Jens Axboe <axboe@kernel.dk>

fs/io-wq.c

@@ -240,7 +240,8 @@ static void io_wqe_wake_worker(struct io_wqe *wqe, struct io_wqe_acct *acct)
 	 * Most likely an attempt to queue unbounded work on an io_wq that
 	 * wasn't setup with any unbounded workers.
 	 */
-	WARN_ON_ONCE(!acct->max_workers);
+	if (unlikely(!acct->max_workers))
+		pr_warn_once("io-wq is not configured for unbound workers");
 
 	rcu_read_lock();
 	ret = io_wqe_activate_free_worker(wqe);
@@ -901,6 +902,8 @@ struct io_wq *io_wq_create(unsigned bounded, struct io_wq_data *data)
 
 	if (WARN_ON_ONCE(!data->free_work || !data->do_work))
 		return ERR_PTR(-EINVAL);
+	if (WARN_ON_ONCE(!bounded))
+		return ERR_PTR(-EINVAL);
 
 	wq = kzalloc(struct_size(wq, wqes, nr_node_ids), GFP_KERNEL);
 	if (!wq)