[Bugs] [Bug 1630145] New: Geo-rep: Few workers fails to start with out any failure

[bugzilla at redhat.com]

https://bugzilla.redhat.com/show_bug.cgi?id=1630145

            Bug ID: 1630145
           Summary: Geo-rep: Few workers fails to start with out any
                    failure
           Product: GlusterFS
           Version: 4.1
         Component: geo-replication
          Assignee: bugs at gluster.org
          Reporter: khiremat at redhat.com
                CC: bugs at gluster.org
        Depends On: 1614799
            Blocks: 1623749



+++ This bug was initially created as a clone of Bug #1614799 +++

Description of problem:
Few workers fails to start with out any failure.

Version-Release number of selected component (if applicable):
mainline

How reproducible:
Seen only while running upstream regression test case
prove -v tests/00-geo-rep/georep-basic-dr-rsync.t

Steps to Reproduce:
1. Get upstream gluster source code
2. source install gluster
3. prove -v tests/00-geo-rep/georep-basic-dr-rsync.t

Actual results:
one of the worker fails to start without any log

Expected results:
No worker should fail to start

Additional info:

--- Additional comment from Worker Ant on 2018-08-10 08:41:14 EDT ---

REVIEW: https://review.gluster.org/20704 (geo-rep: Fix deadlock during worker
start) posted (#1) for review on master by Kotresh HR

--- Additional comment from Worker Ant on 2018-08-12 23:52:34 EDT ---

COMMIT: https://review.gluster.org/20704 committed in master by "Amar Tumballi"
<amarts at redhat.com> with a commit message- geo-rep: Fix deadlock during worker
start

Analysis:
Monitor process spawns monitor threads (one per brick).
Each monitor thread, forks worker and agent processes.
Each monitor thread, while intializing, updates the
monitor status file. It is synchronized using flock.
The race is that, some thread can fork worker while
other thread opened the status file resulting in
holding the reference of fd in worker process.

Cause:
flock gets unlocked either by specifically unlocking it
or by closing all duplicate fds referring to the file.
The code was relying on fd close, hence a reference
in worker/agent process by fork could cause the deadlock.

Fix:
1. flock is unlocked specifically.
2. Also made sure to update status file in approriate places so that
the reference is not leaked to worker/agent process.

With this fix, both the deadlock and possible fd
leaks is solved.

fixes: bz#1614799
Change-Id: I0d1ce93072dab07d0dbcc7e779287368cd9f093d
Signed-off-by: Kotresh HR <khiremat at redhat.com>


Referenced Bugs:

https://bugzilla.redhat.com/show_bug.cgi?id=1614799
[Bug 1614799] Geo-rep: Few workers fails to start with out any failure
https://bugzilla.redhat.com/show_bug.cgi?id=1623749
[Bug 1623749] Geo-rep: Few workers fails to start with out any failure
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