Bug 1465735

Summary: non root user run kdumpctl cause dead loop
Product: [Fedora] Fedora Reporter: Dave Young <ruyang>
Component: kexec-toolsAssignee: Ziyue Yang <ziyang>
Status: CLOSED RAWHIDE QA Contact: Fedora Extras Quality Assurance <extras-qa>
Severity: unspecified Docs Contact:
Priority: unspecified    
Version: rawhideCC: bhe, kdump-team-bugs, ruyang, xlpang
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: 1474174 (view as bug list) Environment:
Last Closed: 2017-07-14 08:11:15 UTC Type: Bug
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Description Dave Young 2017-06-28 04:57:19 UTC
Description of problem:
Run `kdumpctl status` as normal user, get below error messages:

Another app is currently holding the kdump lock; waiting for it to exit...
flock: 9: Bad file descriptor
Another app is currently holding the kdump lock; waiting for it to exit...
flock: 9: Bad file descriptor
Another app is currently holding the kdump lock; waiting for it to exit...
flock: 9: Bad file descriptor
Another app is currently holding the kdump lock; waiting for it to exit...
flock: 9: Bad file descriptor
Another app is currently holding the kdump lock; waiting for it to exit...
flock: 9: Bad file descriptor
Another app is currently holding the kdump lock; waiting for it to exit...
flock: 9: Bad file descriptor
Another app is currently holding the kdump lock; waiting for it to exit...
flock: 9: Bad file descriptor
Another app is currently holding the kdump lock; waiting for it to exit...
flock: 9: Bad file descriptor
Another app is currently holding the kdump lock; waiting for it to exit..

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Comment 1 Ziyue Yang 2017-07-03 07:43:23 UTC
This bug is caused by behavior difference between bash and sh(bash in posix).

In the function single_instance_lock in kdumpctl script, there is

exec 9>/var/lock/kdump

which will fail in user mode. However, this fail will cause script exit under bash and non-exit under sh, causing infinite loop because the flock will always fail.

According to the 15th item in
ftp://ftp.gnu.org/old-gnu/Manuals/bash-2.02/html_node/bashref_66.html

If a POSIX.2 special builtin returns an error status, a non-interactive shell exits.

And according to
https://www.gnu.org/software/bash/manual/html_node/Special-Builtins.html

These are the POSIX special builtins:

break : . continue eval exec exit export readonly return set
shift trap unset

I suggest fixing the bug by checking exec return value.

Comment 2 Ziyue Yang 2017-07-03 07:43:50 UTC
Sorry it should be the 16th item.