tree 3b65aa0ce0a8b00ce0fdcf81be16e0d3d0b704f6
parent 726783db183829a7ab4cd0401d493ffd44781f39
author Willy Tarreau <w@1wt.eu> 1625552960 +0200
committer Willy Tarreau <w@1wt.eu> 1625561539 +0200
encoding latin1

BUG/MEDIUM: sock: make sure to never miss early connection failures

As shown in issue #1251, it is possible for a connect() to report an
error directly via the poller without ever reporting send readiness,
but currentlt sock_conn_check() manages to ignore that situation,
leading to high CPU usage as poll() wakes up on these FDs.

The bug was apparently introduced in 1.5-dev22 with commit fd803bb4d
("MEDIUM: connection: add check for readiness in I/O handlers"), but
was likely only woken up by recent changes to conn_fd_handler() that
made use of wakeups instead of direct calls between 1.8 and 1.9,
voiding any chance to catch such errors in the early recv() callback.

The exact sequence that leads to this situation remains obscure though
because the poller does not report send readiness nor does it report an
error. Only HUP and IN are reported on the FD. It is also possible that
some recent kernel updates made this condition appear while it never
used to previously.

This needs to be backported to all stable branches, at least as far
as 2.0. Before 2.2 the code was in tcp_connect_probe() in proto_tcp.c.