io_uring: fix unchecked error in switch_start()

io_rsrc_node_switch_start() can fail, don't forget to check returned
error code.

Reported-by: syzbot+a4715dd4b7c866136f79@syzkaller.appspotmail.com
Fixes: eae071c ("io_uring: prepare fixed rw for dynanic buffers")
Signed-off-by: Pavel Begunkov <asml.silence@gmail.com>
Link: https://lore.kernel.org/r/c4c06e2f3f0c8e43bd8d0a266c79055bcc6b6e60.1619693112.git.asml.silence@gmail.com
Signed-off-by: Jens Axboe <axboe@kernel.dk>

Author: isilence

fs/io_uring.c

@@ -9627,7 +9627,9 @@ static int io_uring_create(unsigned entries, struct io_uring_params *p,
 	if (ret)
 		goto err;
 	/* always set a rsrc node */
-	io_rsrc_node_switch_start(ctx);
+	ret = io_rsrc_node_switch_start(ctx);
+	if (ret)
+		goto err;
 	io_rsrc_node_switch(ctx, NULL);
 
 	memset(&p->sq_off, 0, sizeof(p->sq_off));