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Date: Thu, 09 Nov 2000 15:27:16 -0500
From: Jeff Garzik <jgarzik@mandrakesoft.com>
Organization: MandrakeSoft
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To: root@chaos.analogic.com
CC: Brian Gerst <bgerst@didntduck.org>,
        Linux kernel <linux-kernel@vger.kernel.org>
Subject: Re: Module open() problems, Linux 2.4.0
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"Richard B. Johnson" wrote:
> 
> On Thu, 9 Nov 2000, Brian Gerst wrote:
> 
> > "Richard B. Johnson" wrote:
> > >
> > > `lsmod` shows that a device is open twice when using Linux-2.4.0-test9
> > > when, in fact, it has been opened only once.
> > >
> 
> > >
> > > When the module is closed, the use-count goes to zero as expected.
> > > However, a single open() causes the use-count to be 2.
> >
> > This is harmless.  It is caused by a try_inc_mod_count(module) in the
> > function calling device_open(), which is the proper way for module
> > locking to be handled when not holding the BKL.  You can keep the
> > MOD_INC_USE_COUNT in the device driver for compatability with 2.2.
> >
> >                               Brian Gerst
> 
> This may be, as you say, "harmless". It is, however, a bug. The
> reporting must be correct or large complex systems can't be
> developed or maintained.
> 
> I had two persons, working nearly a week, trying to find out
> what one of over 200 processes had a device open when only
> one was supposed to have it opened. --Err we have to check
> our work here. The fact that something "works" is not
> sufficient.

There is NO guarantee that module use count == device open count.  Never
has been, AFAIK.  It just happens to work out that way on a lot of
pre-2.4 code.

The kernel is free to bump the module reference count up and down as it
pleases.  For example, if a driver creates a kernel thread, that will
increase its module usage count by one, for the duration of the kernel
thread's lifetime.

The only rule is that you cannot unload a module until its use count it
zero.  

	Jeff


-- 
Jeff Garzik             |
Building 1024           | Would you like a Twinkie?
MandrakeSoft            |
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