linux-kernel - module refcnt underflow

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Message-ID: <CAKi4VA+RBToB3fO21N-QWdPZeqGpg1ASHzn3vwB9t64ApdwrsA@mail.gmail.com>
Date:	Wed, 26 Jun 2013 13:20:16 -0300
From:	Lucas De Marchi <lucas.de.marchi@...il.com>
To:	lkml <linux-kernel@...r.kernel.org>,
	Rusty Russell <rusty@...tcorp.com.au>,
	linux-modules <linux-modules@...r.kernel.org>
Subject: module refcnt underflow

Hi,

While checking somethings for a next release of kmod I noticed this
strange thing:

cat /sys/module/acpi_cpufreq/refcnt
18446744073709551614

We outputs this as "-1" in lsmod because we treat the value as signed.
I was just going to change it to unsigned to make it compatible with
what module-init-tools does but... For me it looks like a bug in the
kernel since in this file we just have the output of
kernel/module.c:module_refcount()

I have this behavior on 3.9.2 but judging by the missing commits in
kernel/module.c, this would also happen in latest head. I've never
seen such a value so I guess it might be difficult to reproduce it
again.

Any hints on what could cause decs to be greater than incs in module_refcount()?

--

Lucas De Marchi
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