linux-kernel - RFH: stale (f)lock in /proc/locks

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Date:	Wed, 14 Oct 2015 10:30:11 +0200
From:	Philipp Hahn <pmhahn@...ahn.de>
To:	linux-kernel@...r.kernel.org
Subject: RFH: stale (f)lock in /proc/locks - process no longer exists

Hi,

I have several shell scripts using "/usr/bin/flock -x
/run/lock/jenkins-ip.lock" to acquiring the exclusive lock. Today they
hang, while the lock is owned by a process which no longer exists:

# ls -i /run/lock/jenkins-ip.lock
766711440 /run/lock/jenkins-ip.lock

# grep 766711440 /proc/locks
1: FLOCK  ADVISORY  WRITE 1722 00:12:766711440 0 EOF
1: -> FLOCK  ADVISORY  WRITE 1725 00:12:766711440 0 EOF
1: -> FLOCK  ADVISORY  WRITE 20432 00:12:766711440 0 EOF
1: -> FLOCK  ADVISORY  WRITE 20618 00:12:766711440 0 EOF
1: -> FLOCK  ADVISORY  WRITE 16235 00:12:766711440 0 EOF
1: -> FLOCK  ADVISORY  WRITE 21757 00:12:766711440 0 EOF
1: -> FLOCK  ADVISORY  WRITE 29151 00:12:766711440 0 EOF

# lslocks -o COMMAND,PID,TYPE,MODE,PATH,BLOCKER
COMMAND           PID  TYPE MODE   PATH                      BLOCKER
(unknown)        5852 FLOCK WRITE  /run
cron              489 FLOCK WRITE  /run/crond.pid
libvirtd          506 POSIX WRITE  /run/libvirtd.pid
flock           29151 FLOCK WRITE* /run/lock/jenkins-ip.lock    1722
flock           21757 FLOCK WRITE* /run/lock/jenkins-ip.lock    1722
flock           16235 FLOCK WRITE* /run/lock/jenkins-ip.lock    1722
flock           20618 FLOCK WRITE* /run/lock/jenkins-ip.lock    1722
flock           20432 FLOCK WRITE* /run/lock/jenkins-ip.lock    1722
flock            1725 FLOCK WRITE* /run/lock/jenkins-ip.lock    1722
(unknown)        1722 FLOCK WRITE  /run/lock

# ps 1722
  PID TTY      STAT   TIME COMMAND

# uname -a
Linux test4 3.16.0-4-amd64 #1 SMP Debian 3.16.7-ckt11-1+deb8u3
(2015-08-04) x86_64 GNU/Linux

1. How can this happen?
   My understanding is, that all files are closed on process exit and
that all locks are released then. Did I miss something.

2. How can I release that lock?

Thanks in advance
Philipp
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