linux-kernel - Re: kobject_put vs module unload

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Message-ID: <AANLkTikg7vAG4-E=BD_sC=63R8fDCfEi_wiqnxDnUnK=@mail.gmail.com>
Date:	Sat, 8 Jan 2011 18:23:16 +0100
From:	Kay Sievers <kay.sievers@...y.org>
To:	Mikulas Patocka <mpatocka@...hat.com>
Cc:	Greg KH <gregkh@...e.de>, linux-kernel@...r.kernel.org,
	dm-devel@...hat.com
Subject: Re: kobject_put vs module unload

On Sat, Jan 8, 2011 at 14:19, Mikulas Patocka <mpatocka@...hat.com> wrote:
> On Fri, 7 Jan 2011, Greg KH wrote:

>> > 4) the reference obtained at point 1) is dropped, kobject reference count
>> > reaches zero and the release callback is called. But that callback points
>> > to an unloaded module and causes a crash.
>> >
>> > How is it solved? Am I missing something?
>>
>> You have the code that creates and frees the object, to not be in the
>> module that could have been unloaded.  It's really just that simple.
>
> If the whole device mapper subsystem can be a module, where can I put the
> code?
>
> I think a similar bug exists in md, it can also be unloaded as a module
> and it has "release" method in its module code.

If you still have data structures hanging around, these structures are
supposed to take a reference on the module -- and you can not unload
the module as long as this is the case.

Kay
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