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Subject: Re: kobject ->k_name memory leak
From: Kay Sievers <kay.sievers@vrfy.org>
To: Alexey Dobriyan <adobriyan@gmail.com>
Cc: Greg KH <greg@kroah.com>, Greg KH <gregkh@suse.de>,
       Alexey Dobriyan <adobriyan@sw.ru>, akpm@osdl.org,
       linux-kernel@vger.kernel.org
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Date: Sat, 15 Dec 2007 16:19:16 +0100
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On Sat, 2007-12-15 at 16:34 +0300, Alexey Dobriyan wrote:
> On Fri, Dec 14, 2007 at 01:48:23PM -0800, Greg KH wrote:
> > On Mon, Dec 03, 2007 at 01:25:51PM -0800, Greg KH wrote:
> > > On Tue, Dec 04, 2007 at 12:09:59AM +0300, Alexey Dobriyan wrote:
> > > > On Mon, Dec 03, 2007 at 12:47:16PM -0800, Greg KH wrote:
> > > > > On Mon, Dec 03, 2007 at 12:26:07PM +0300, Alexey Dobriyan wrote:
> > > > > > Hi, Greg!
> > > > > > 
> > > > > > Commit ce2c9cb0259acd2aed184499ebe41ab00da13b25 aka
> > > > > > "kobject: remove the static array for the name" introduced memory leak
> > > > > > of a module name after modprobe/rmmod. Apparently for modules ->release
> > > > > > callback is NULL.
> > > > > > 
> > > > > > kobject_cleanup: ->release = 00000000, name = 'foo_sysctl'
> > > > > > Pid: 1927, comm: rmmod Not tainted 2.6.24-rc3-e1cca7e8d484390169777b423a7fe46c7021fec1 #5
> > > > > >  [<c10d4a58>] kobject_cleanup+0xb8/0xc0
> > > > > >  [<c10d4a60>] kobject_release+0x0/0x10
> > > > > >  [<c10d587b>] kref_put+0x2b/0xa0
> > > > > >  [<c11dbe85>] _spin_unlock+0x25/0x40
> > > > > >  [<c1045b78>] free_module+0x78/0xd0
> > > > > >  [<c104773f>] sys_delete_module+0x12f/0x1a0
> > > > > 
> > > > > Hm, _which_ kobject associated with a module, there are 3 of them I
> > > > > think :)
> > > > 
> > > > Ouch!
> > > > 
> > > > > They should all have a release function, and if they do not, we think
> > > > > it's a "static" kobject and it is not safe to free that name.
> > > > > 
> > > > > I've been working on cleaning this up a lot in the -mm tree with over 80
> > > > > patches for the kset/kobject apis and interfaces.
> > > > > 
> > > > > But if we have a dynamic kobject, and we aren't freeing it properly,
> > > > > please let me know which one it is and I'll work to fix it for 2.6.24.
> > > > 
> > > > The one which is passed to kobject_set_name() in mod_sysfs_init()..
> > > 
> > > That one should be set to the module_ktype, which is in kernel/params.c,
> > > so the release function there should... oh crap, there is no release
> > > function.  That's a bug.  After I get out of meetings tonight I'll write
> > > up a patch for that, unless someone beats me to it :)
> > 
> > Ok, this is a mess.  We can't really have a release function for this
> > kobject, as the structure it is embedded it has it's own memory
> > management issues.
> > 
> > To fix this properly is going to take some major kobject/module surgery,
> > it's not a simple fix at all.  I'll tackle it for 2.6.25, as it fits in
> > nicely with the other kobject rework that I've already done in the -mm
> > tree.
> > 
> > So, for now, can we just live with this tiny memory leak on module
> > unload?
> 
> For the record, this leak screws any testing one can do wrt module
> unload races. You can't really leave box overnight running
> modprobe/rmmod in a loop, because OOM killer will finally kick in.
> Hey, this is exactly how it was noticed at all.
> 
> > Or is the above trace something that users will see when unloading
> > modules?
> 
> No, it's added debugging.

Can't we add an empty release function? It would free the name with the
current logic, right?

Kay

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