tree f4bca4916261f40f1f73af771df343825cc4954e
parent beec7eae28a8c776c15f83d9b41c23cb4175693d
author Amaury Denoyelle <adenoyelle@haproxy.com> 1624007496 +0200
committer Christopher Faulet <cfaulet@haproxy.com> 1624456357 +0200

BUG/MAJOR: server: fix deadlock when changing maxconn via agent-check

The server_parse_maxconn_change_request locks the server lock. However,
this function can be called via agent-checks or lua code which already
lock it. This bug has been introduced by the following commit :

  commit 79a88ba3d09f7e2b73ae27cb5d24cc087a548fa6
  BUG/MAJOR: server: prevent deadlock when using 'set maxconn server'

This commit tried to fix another deadlock with can occur because
previoulsy server_parse_maxconn_change_request requires the server lock
to be held. However, it may call internally process_srv_queue which also
locks the server lock. The locking policy has thus been updated. The fix
is functional for the CLI 'set maxconn' but fails to address the
agent-check / lua counterparts.

This new issue is fixed in two steps :
- changes from the above commit have been reverted. This means that
  server_parse_maxconn_change_request must again be called with the
  server lock.

- to counter the deadlock fixed by the above commit, process_srv_queue
  now takes an argument to render the server locking optional if the
  caller already held it. This is only used by
  server_parse_maxconn_change_request.

The above commit was subject to backport up to 1.8. Thus this commit
must be backported in every release where it is already present.

(cherry picked from commit 0274286dd3768c0d5e58588a1cb7e7e710fbc9d4)
Signed-off-by: Christopher Faulet <cfaulet@haproxy.com>