io_uring/poll: fix POLLERR handling

JIRA: https://issues.redhat.com/browse/RHEL-106845

commit c7cafd5
Author: Pavel Begunkov <asml.silence@gmail.com>
Date:   Wed Jul 16 17:20:17 2025 +0100

    io_uring/poll: fix POLLERR handling

    8c8492c ("io_uring/net: don't retry connect operation on EPOLLERR")
    is a little dirty hack that
    1) wrongfully assumes that POLLERR equals to a failed request, which
    breaks all POLLERR users, e.g. all error queue recv interfaces.
    2) deviates the connection request behaviour from connect(2), and
    3) racy and solved at a wrong level.

    Nothing can be done with 2) now, and 3) is beyond the scope of the
    patch. At least solve 1) by moving the hack out of generic poll handling
    into io_connect().

    Cc: stable@vger.kernel.org
    Fixes: 8c8492c ("io_uring/net: don't retry connect operation on EPOLLERR")
    Signed-off-by: Pavel Begunkov <asml.silence@gmail.com>
    Link: https://lore.kernel.org/r/3dc89036388d602ebd84c28e5042e457bdfc952b.1752682444.git.asml.silence@gmail.com
    Signed-off-by: Jens Axboe <axboe@kernel.dk>

Signed-off-by: Ming Lei <ming.lei@redhat.com>

Author: Ming Lei

io_uring/net.c

@@ -1665,9 +1665,11 @@ int io_connect(struct io_kiocb *req, unsigned int issue_flags)
 	int ret;
 	bool force_nonblock = issue_flags & IO_URING_F_NONBLOCK;
 
-	if (unlikely(req->flags & REQ_F_FAIL)) {
-		ret = -ECONNRESET;
-		goto out;
+	if (connect->in_progress) {
+		struct poll_table_struct pt = { ._key = EPOLLERR };
+
+		if (vfs_poll(req->file, &pt) & EPOLLERR)
+			goto get_sock_err;
 	}
 
 	file_flags = force_nonblock ? O_NONBLOCK : 0;
@@ -1692,8 +1694,10 @@ int io_connect(struct io_kiocb *req, unsigned int issue_flags)
 		 * which means the previous result is good. For both of these,
 		 * grab the sock_error() and use that for the completion.
 		 */
-		if (ret == -EBADFD || ret == -EISCONN)
+		if (ret == -EBADFD || ret == -EISCONN) {
+get_sock_err:
 			ret = sock_error(sock_from_file(req->file)->sk);
+		}
 	}
 	if (ret == -ERESTARTSYS)
 		ret = -EINTR;

io_uring/poll.c

@@ -273,8 +273,6 @@ static int io_poll_check_events(struct io_kiocb *req, io_tw_token_t tw)
 				return IOU_POLL_REISSUE;
 			}
 		}
-		if (unlikely(req->cqe.res & EPOLLERR))
-			req_set_fail(req);
 		if (req->apoll_events & EPOLLONESHOT)
 			return IOU_POLL_DONE;