Race condition on restart

Paul Scott sales at edenusa.com
Fri Apr 28 04:54:37 UTC 2017

This is exactly what I thought.  Every time I restarted MailScanner, it caused this problem and the system had to be restarted.


Paul Scott, Engineer
Eden USA, Incorporated
Event Production Services Since 1995
Los Angeles-Las Vegas-New York
sales at edenusa.com OR edenusasales at gmail.com
Telephone(s): 866.501.3336 OR 951.505.6967
Fax: 866.502.3336 

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-----Original Message-----
From: MailScanner [mailto:mailscanner-bounces+sales=edenusa.com at lists.mailscanner.info] On Behalf Of David While
Sent: Wednesday, April 26, 2017 9:39 AM
To: mailscanner at lists.mailscanner.info
Subject: Race condition on restart

There is a bug in MailScanner which leads to a race condition.

The init script which starts/stops & restarts MailScanner removes the PID file when MailScanner is stopped.

Unfortunately when MailScanner is issued with a SIGTERM (when issuing a restart or stop) then it also removes the PID file (line 1419 in MailScanner).

What is happening is that the init script issues the kill and then continues. This doesn't kill MailScanner but simply sends the signal. 
MailScanner does some processing before dying. Consequently there is now a race as to who will remove the PID file. The worst case is that it is removed after MailScanner has been restarted. This leads to the hourly ms-check constantly restarting MailScanner.

I fixed this in the init script by:

1. Removing the following lines from do_stop

                     # remove pid file
                     if [ -f $PIDFILE ] ; then
                                 rm -f $PIDFILE

2. Moving the following lines from restart to do_stop where the above lines were removed

         while [ "$x" -lt 300 -a -f $PIDFILE ]; do
            i=$(( (i+1) %4 ));
            printf "\r${s:$i:1}";
            sleep .1;

What this does is wait for MailScanner to die and remove the PID file before continuing.

I don't think this is a permament fix as there ought to be a check that it has not timed out before continuing.

David While

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