Stefan Metzmacher bc16a8abe3 lib/tsocket: avoid endless cpu-spinning in tstream_bsd_fde_handler() ... There were some reports that strace output an LDAP server socket is in CLOSE_WAIT state, returning EAGAIN for writev over and over (after a call to epoll() each time). In the tstream_bsd code the problem happens when we have a pending writev_send, while there's no readv_send pending. In that case we still ask for TEVENT_FD_READ in order to notice connection errors early, so we try to call writev even if the socket doesn't report TEVENT_FD_WRITE. And there are situations where we do that over and over again. It happens like this with a Linux kernel: tcp_fin() has this: struct tcp_sock *tp = tcp_sk(sk); inet_csk_schedule_ack(sk); sk->sk_shutdown |= RCV_SHUTDOWN; sock_set_flag(sk, SOCK_DONE); switch (sk->sk_state) { case TCP_SYN_RECV: case TCP_ESTABLISHED: /* Move to CLOSE_WAIT */ tcp_set_state(sk, TCP_CLOSE_WAIT); inet_csk_enter_pingpong_mode(sk); break; It means RCV_SHUTDOWN gets set as well as TCP_CLOSE_WAIT, but sk->sk_err is not changed to indicate an error. tcp_sendmsg_locked has this: ... err = -EPIPE; if (sk->sk_err || (sk->sk_shutdown & SEND_SHUTDOWN)) goto do_error; while (msg_data_left(msg)) { int copy = 0; skb = tcp_write_queue_tail(sk); if (skb) copy = size_goal - skb->len; if (copy <= 0 || !tcp_skb_can_collapse_to(skb)) { bool first_skb; new_segment: if (!sk_stream_memory_free(sk)) goto wait_for_space; ... wait_for_space: set_bit(SOCK_NOSPACE, &sk->sk_socket->flags); if (copied) tcp_push(sk, flags & ~MSG_MORE, mss_now, TCP_NAGLE_PUSH, size_goal); err = sk_stream_wait_memory(sk, &timeo); if (err != 0) goto do_error; It means if (sk->sk_err || (sk->sk_shutdown & SEND_SHUTDOWN)) doesn't hit as we only have RCV_SHUTDOWN and sk_stream_wait_memory returns -EAGAIN. tcp_poll has this: if (sk->sk_shutdown & RCV_SHUTDOWN) mask |= EPOLLIN | EPOLLRDNORM | EPOLLRDHUP; So we'll get EPOLLIN | EPOLLRDNORM | EPOLLRDHUP triggering TEVENT_FD_READ and writev/sendmsg keeps getting EAGAIN. So we need to always clear TEVENT_FD_READ if we don't have readable handler in order to avoid burning cpu. But we turn it on again after a timeout of 1 second in order to monitor the error state of the connection. And now that our tsocket_bsd_error() helper checks for POLLRDHUP, we can check if the socket is in an error state before calling the writable handler when TEVENT_FD_READ was reported. Only on error we'll call the writable handler, which will pick the error without calling writev(). BUG: https://bugzilla.samba.org/show_bug.cgi?id=15202 Signed-off-by: Stefan Metzmacher <metze@samba.org> Reviewed-by: Ralph Boehme <slow@samba.org> (cherry picked from commit e232ba946f)		2022-10-31 14:30:09 +00:00
..
tests	lib/tsocket: Add tests for loop on EAGAIN	2022-10-31 14:30:08 +00:00
doxy.config
tsocket_bsd.c	lib/tsocket: avoid endless cpu-spinning in tstream_bsd_fde_handler()	2022-10-31 14:30:09 +00:00
tsocket_guide.txt	tsocket: Fix a few typos	2021-01-14 13:29:35 +00:00
tsocket_helpers.c	lib/tsocket: Free subreq as soon as possible	2021-07-08 10:21:25 +00:00
tsocket_internal.h
tsocket.c
tsocket.h	lib/tsocket: new function to parse host port strs.	2021-09-28 09:44:35 +00:00
wscript_build	lib/tsocket: Add tests for loop on EAGAIN	2022-10-31 14:30:08 +00:00