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Bug 437416 - dlm_tool lockdump give garbage or no output with large lock counts
dlm_tool lockdump give garbage or no output with large lock counts
Product: Red Hat Enterprise Linux 5
Classification: Red Hat
Component: cman (Show other bugs)
All Linux
low Severity low
: rc
: ---
Assigned To: David Teigland
GFS Bugs
Depends On:
  Show dependency treegraph
Reported: 2008-03-13 18:18 EDT by Dean Jansa
Modified: 2010-01-05 12:49 EST (History)
2 users (show)

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Doc Type: Bug Fix
Doc Text:
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Last Closed: 2010-01-05 12:49:50 EST
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RHEL 7.3 requirements from Atomic Host:
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Description Dean Jansa 2008-03-13 18:18:36 EDT
Description of problem:

If I create > ~ 2930 locks dlm_tool lockdump  either displays garbage data or
nothing at all.  Releasing some of the locks "fixes" the issue.

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

How reproducible:

Every time

Steps to Reproduce:
1. grab more than 3000 locks
2. dlm_tool lockdump myns
Comment 1 Dean Jansa 2008-03-14 16:19:22 EDT
As Dave suggested, a cat of the _locks file in /sys/kerne/debug/dlm shows the

[root@marathon-01 dlm]# pwd
[root@marathon-01 dlm]# cat default_locks 
cat: default_locks: Cannot allocate memory

If you run dlm_tool lockdump default when the above happens you get:
[root@marathon-01 dlm]# dlm_tool lockdump default
invalid debugfs line 0: id nodeid remid pid xid exflags flags sts grmode rqmode
time_ms r_nodeid r_len r_name

The following patch has dlm_tool report an error of the initial fgets returns an
error rather than printing out either the first line of the file or garbage:

[root@marathon-01 dlm_tool]# ./dlm_tool lockdump default
can't read /sys/kernel/debug/dlm/default_locks: Cannot allocate memory
[root@marathon-01 dlm_tool]# 

--- ../main.c   2008-03-14 14:56:03.000000000 -0500
+++ main.c      2008-03-14 15:16:13.000000000 -0500
@@ -332,7 +332,12 @@
        /* skip the header on the first line */
-       fgets(line, LOCK_LINE_MAX, file);
+       if (!fgets(line, LOCK_LINE_MAX, file)) {
+               if (!feof(file)) {
+                       fprintf(stderr, "can't read %s: %s\n", path,
+               }
+               return;
+       }
        while (fgets(line, LOCK_LINE_MAX, file)) {
                rv = sscanf(line, "%x %d %x %u %llu %x %x %hhd %hhd %hhd %u %d %d",


Comment 2 David Teigland 2010-01-05 12:49:50 EST
The reason I've not done anything with this is that I tested with many times this number of locks and never had a problem dumping them all.  Because this is only a cosmetic issue, it's not worth the effort of getting the patch into RHEL and I'm going to just drop it.

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