Messages in this thread | | | Date | Wed, 11 Feb 2009 13:55:08 +0300 | Subject | GFS2 file locking issues | From | Kirill Kuvaldin <> |
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Hi,
I'm trying to understand how the FS locking mechanism should work.
I'm running a clustered GFS2 across two nodes, each node is a Xen domU. To check if locking works correctly I wrote the simple perl script below. Basically the script opens a file, locks it to prevent others from writing into it, writes 20 lines into it, then unlocks and closes.
------------------------------------------------------------------------------ #!/usr/bin/perl
# usage: # lock.pl filename uniq # filename - file name being written to # uniq - an unique label to distinguish output of different processes
use strict; use Time::HiRes qw(sleep); use FileHandle; use Fcntl ':flock';
my $filename = $ARGV[0]; my $uniq = $ARGV[1];
open FH, '>>', $filename or die $!; flock(FH,LOCK_EX) or die $!; FH->autoflush(1);
for (1..20) { print FH "$uniq\n"; sleep (0.1); }
flock(FH,LOCK_UN); close FH; ------------------------------------------------------------------------------
I ran that script on both nodes simultaneously with commands:
vm01# perl lock.pl /gfs2/testfile a vm02# perl lock.pl /gfs2/testfile b
Then to my surprise "a"s and "b"s are randomly shuffled in the testfile like
... a a b a b b ...
whereas I supposed it should have been like
... a a a b b b ...
It looks like either locking is broken in my GFS2 (I use kernel 2.6.18-92.el5xen for CentOS 5.2) or my understanding of locking isn't correct. I also tested the script on GFS1 and OCFS2 and it worked well, i.e. the output was correct.
Thanks, Kirill
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