tree cf57dab4230918a0116f2fb01d891c7e1a60bc0a
parent 19490907b3836369215a9860f1bd6d2bc3297937
author Willy Tarreau <w@1wt.eu> 1600874242 +0200
committer Willy Tarreau <w@1wt.eu> 1601034407 +0200
encoding latin1

BUG/MEDIUM: listeners: do not pause foreign listeners

There's a nasty case with listeners that belong to foreign processes.
If a proxy is defined this way:

     global
         nbproc 2

     frontend f
         bind :1111 process 1
         bind :2222 process 2

and if stats expose-fd listeners is set, the listeners' FDs will not
be closed on the processes that don't use them. At this point it's not
a big deal, except that they're shared between processes and that a
"disable frontend f" issued on one process will pause all of them and
cause the other process to see accept() fail, turning its own listener
to state LI_LIMITED to try to leave it some time to recover. But it
will never recover, even after an enable.

The root cause of the issue is that the ZOMBIE state doesn't cover
this situation since it's only for a proxy being entirely bound to a
process.

What we do here to address this is that we refrain from pausing a
file descriptor that belongs to a foreign process in pause_listener().
This definitely solves the problem. A similar test is present in
resume_listener() and is the reason why the FD doesn't recover upon the
"enable" action by the way.

This ought to be backported to 1.8 where seamless reload was integrated.

The config above should be sufficient to validate that the fix works;
after a pair of "disable/enable frontend" no process will handle the
traffic to one of the ports anymore.