io_uring: carve io_poll_check_events fast path

The fast path in io_poll_check_events() is when we have only one
(i.e. master) reference. Move all verification, cancellations
checks, edge case handling and so on under a common if.
Signed-off-by: Pavel Begunkov <asml.silence@gmail.com>
Link: https://lore.kernel.org/r/8c21c5d5e027e32dc553705e88796dec79ff6f93.1669821213.git.asml.silence@gmail.comSigned-off-by: Jens Axboe <axboe@kernel.dk>

io_uring/poll.c

@@ -247,28 +247,31 @@ static int io_poll_check_events(struct io_kiocb *req, bool *locked)
 	do {
 		v = atomic_read(&req->poll_refs);
 
-		/* tw handler should be the owner, and so have some references */
+		if (unlikely(v != 1)) {
+			/* tw should be the owner and so have some refs */
 			if (WARN_ON_ONCE(!(v & IO_POLL_REF_MASK)))
 				return IOU_POLL_DONE;
 			if (v & IO_POLL_CANCEL_FLAG)
 				return -ECANCELED;
 			/*
 			 * cqe.res contains only events of the first wake up
-		 * and all others are be lost. Redo vfs_poll() to get
+			 * and all others are to be lost. Redo vfs_poll() to get
 			 * up to date state.
 			 */
 			if ((v & IO_POLL_REF_MASK) != 1)
 				req->cqe.res = 0;
+
 			if (v & IO_POLL_RETRY_FLAG) {
 				req->cqe.res = 0;
 				/*
 				 * We won't find new events that came in between
-			 * vfs_poll and the ref put unless we clear the flag
-			 * in advance.
+				 * vfs_poll and the ref put unless we clear the
+				 * flag in advance.
 				 */
 				atomic_andnot(IO_POLL_RETRY_FLAG, &req->poll_refs);
 				v &= ~IO_POLL_RETRY_FLAG;
 			}
+		}
 
 		/* the mask was stashed in __io_poll_execute */
 		if (!req->cqe.res) {