netdev - Re: [PATCH net] net: mvpp2: debugfs: fix problem with previous memory leak fix

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Message-ID: <Yy/8FawjLnaE2Swj@shell.armlinux.org.uk>
Date:   Sun, 25 Sep 2022 07:58:29 +0100
From:   "Russell King (Oracle)" <linux@...linux.org.uk>
To:     Marcin Wojtas <mw@...ihalf.com>
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        netdev@...r.kernel.org, linux-kernel@...r.kernel.org,
        "David S. Miller" <davem@...emloft.net>,
        Eric Dumazet <edumazet@...gle.com>,
        Jakub Kicinski <kuba@...nel.org>,
        Paolo Abeni <pabeni@...hat.com>, stable <stable@...nel.org>
Subject: Re: [PATCH net] net: mvpp2: debugfs: fix problem with previous
 memory leak fix

On Sun, Sep 25, 2022 at 01:27:06AM +0200, Marcin Wojtas wrote:
> Hi Russell,
> 
> czw., 22 wrz 2022 o 19:08 Marcin Wojtas <mw@...ihalf.com> napisał(a):
> >
> > Hi,
> >
> > Thank you both for the patches.
> >
> >
> > czw., 22 wrz 2022 o 18:05 Russell King (Oracle)
> > <linux@...linux.org.uk> napisał(a):
> > >
> > > On Wed, Sep 21, 2022 at 01:44:44PM +0200, Greg Kroah-Hartman wrote:
> > > > In commit fe2c9c61f668 ("net: mvpp2: debugfs: fix memory leak when using
> > > > debugfs_lookup()"), if the module is unloaded, the directory will still
> > > > be present if the module is loaded again and creating the directory will
> > > > fail, causing the creation of additional child debugfs entries for the
> > > > individual devices to fail.
> > > >
> > > > As this module never cleaned up the root directory it created, even when
> > > > loaded, and unloading/loading a module is not a normal operation, none
> > > > of would normally happen.
> > > >
> > > > To clean all of this up, use a tiny reference counted structure to hold
> > > > the root debugfs directory for the driver, and then clean it up when the
> > > > last user of it is removed from the system.  This should resolve the
> > > > previously reported problems, and the original memory leak that
> > > > fe2c9c61f668 ("net: mvpp2: debugfs: fix memory leak when using
> > > > debugfs_lookup()") was attempting to fix.
> > >
> > > For the record... I have a better fix for this, but I haven't been able
> > > to get it into a state suitable for submission yet.
> > >
> > > http://www.home.armlinux.org.uk/~rmk/misc/mvpp2-debugfs.diff
> > >
> > > Not yet against the net tree. Might have time tomorrow to do that, not
> > > sure at the moment. Medical stuff is getting in the way. :(
> > >
> >
> > I'd lean towards this version - it is a bit more compact. I'll try to
> > test that tomorrow or during the weekend.
> >
> 
> I improved the patch compile and work (tested on my CN913x board).
> Feel free to submit (if you wish, I can do it too - please let me know
> your preference):
> https://github.com/semihalf-wojtas-marcin/Linux-Kernel/commit/0abb75115ffb2772f595bb3346573e27e650018b

I don't see what the compile fixes were in that - it looks like my patch
ported onto current -net. Obvious changes:

- moved mvpp2_dbgfs_exit() declaration from after mvpp2_dbgfs_cleanup()
  to before.
- moved definition of mvpp2_root to the top of the file (as no effect
  on the code.)

and the change to port it:

- dropped my mvpp2_dbgfs_init() hunk (because it's different in -net)
- removed static declaration of mvpp2_root in mvpp2_dbgfs_init()

I'm not seeing any other changes.

Note that Sasha has submitted a revert of Greg's original patch for
mainline, so my original patch should apply as-is if that revert
happens - and I don't see any compile issues with it.

-- 
RMK's Patch system: https://www.armlinux.org.uk/developer/patches/
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