io_uring: refactor io_arm_poll_handler()

gcc 11 goes a weird path and duplicates most of io_arm_poll_handler()
for READ and WRITE cases. Help it and move all pollin vs pollout
specific bits under a single if-else, so there is no temptation for this
kind of unfolding.

before vs after:
   text    data     bss     dec     hex filename
  85362   12650       8   98020   17ee4 ./fs/io_uring.o
  85186   12650       8   97844   17e34 ./fs/io_uring.o

Signed-off-by: Pavel Begunkov <asml.silence@gmail.com>
Link: https://lore.kernel.org/r/1deea0037293a922a0358e2958384b2e42437885.1624739600.git.asml.silence@gmail.com
Signed-off-by: Jens Axboe <axboe@kernel.dk>

fs/io_uring.c

@@ -5172,19 +5172,29 @@ static int io_arm_poll_handler(struct io_kiocb *req)
 	struct io_ring_ctx *ctx = req->ctx;
 	struct async_poll *apoll;
 	struct io_poll_table ipt;
-	__poll_t mask, ret;
+	__poll_t ret, mask = EPOLLONESHOT | POLLERR | POLLPRI;
 	int rw;
 
 	if (!req->file || !file_can_poll(req->file))
 		return IO_APOLL_ABORTED;
 	if (req->flags & REQ_F_POLLED)
 		return IO_APOLL_ABORTED;
-	if (def->pollin)
+	if (!def->pollin && !def->pollout)
+		return IO_APOLL_ABORTED;
+
+	if (def->pollin) {
 		rw = READ;
-	else if (def->pollout)
+		mask |= POLLIN | POLLRDNORM;
+
+		/* If reading from MSG_ERRQUEUE using recvmsg, ignore POLLIN */
+		if ((req->opcode == IORING_OP_RECVMSG) &&
+		    (req->sr_msg.msg_flags & MSG_ERRQUEUE))
+			mask &= ~POLLIN;
+	} else {
 		rw = WRITE;
-	else
-		return IO_APOLL_ABORTED;
+		mask |= POLLOUT | POLLWRNORM;
+	}
+
 	/* if we can't nonblock try, then no point in arming a poll handler */
 	if (!io_file_supports_async(req, rw))
 		return IO_APOLL_ABORTED;
@@ -5193,23 +5203,8 @@ static int io_arm_poll_handler(struct io_kiocb *req)
 	if (unlikely(!apoll))
 		return IO_APOLL_ABORTED;
 	apoll->double_poll = NULL;
-
-	req->flags |= REQ_F_POLLED;
 	req->apoll = apoll;
-
-	mask = EPOLLONESHOT;
-	if (def->pollin)
-		mask |= POLLIN | POLLRDNORM;
-	if (def->pollout)
-		mask |= POLLOUT | POLLWRNORM;
-
-	/* If reading from MSG_ERRQUEUE using recvmsg, ignore POLLIN */
-	if ((req->opcode == IORING_OP_RECVMSG) &&
-	    (req->sr_msg.msg_flags & MSG_ERRQUEUE))
-		mask &= ~POLLIN;
-
-	mask |= POLLERR | POLLPRI;
-
+	req->flags |= REQ_F_POLLED;
 	ipt.pt._qproc = io_async_queue_proc;
 
 	ret = __io_arm_poll_handler(req, &apoll->poll, &ipt, mask,