linux-kernel - Re: [PATCH] mtd: spi-nor: fix memory leak when using debugfs

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Message-ID: <Y+OcZoFhS7HzUifp@kroah.com>
Date:   Wed, 8 Feb 2023 13:58:14 +0100
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     Michael Walle <michael@...le.cc>
Cc:     tudor.ambarus@...rochip.com, pratyush@...nel.org,
        linux-kernel@...r.kernel.org,
        Miquel Raynal <miquel.raynal@...tlin.com>,
        Richard Weinberger <richard@....at>,
        Vignesh Raghavendra <vigneshr@...com>,
        linux-mtd@...ts.infradead.org, stable <stable@...nel.org>
Subject: Re: [PATCH] mtd: spi-nor: fix memory leak when using debugfs_lookup()

On Sat, Sep 24, 2022 at 10:46:22AM +0200, Greg Kroah-Hartman wrote:
> On Fri, Sep 02, 2022 at 04:01:36PM +0200, Michael Walle wrote:
> > Hi,
> > 
> > Am 2022-09-02 15:37, schrieb Greg Kroah-Hartman:
> > > When calling debugfs_lookup() the result must have dput() called on it,
> > > otherwise the memory will leak over time.  Fix this up to be much
> > > simpler logic and only create the root debugfs directory once when the
> > > driver is first accessed.  That resolves the memory leak and makes
> > > things more obvious as to what the intent is.
> > > 
> > > Cc: Tudor Ambarus <tudor.ambarus@...rochip.com>
> > > Cc: Pratyush Yadav <pratyush@...nel.org>
> > > Cc: Michael Walle <michael@...le.cc>
> > > Cc: Miquel Raynal <miquel.raynal@...tlin.com>
> > > Cc: Richard Weinberger <richard@....at>
> > > Cc: Vignesh Raghavendra <vigneshr@...com>
> > > Cc: linux-mtd@...ts.infradead.org
> > > Cc: stable <stable@...nel.org>
> > > Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
> > > ---
> > >  drivers/mtd/spi-nor/debugfs.c | 4 ++--
> > >  1 file changed, 2 insertions(+), 2 deletions(-)
> > > 
> > > diff --git a/drivers/mtd/spi-nor/debugfs.c
> > > b/drivers/mtd/spi-nor/debugfs.c
> > > index df76cb5de3f9..3aab595e82d1 100644
> > > --- a/drivers/mtd/spi-nor/debugfs.c
> > > +++ b/drivers/mtd/spi-nor/debugfs.c
> > > @@ -228,11 +228,11 @@ static void spi_nor_debugfs_unregister(void *data)
> > > 
> > >  void spi_nor_debugfs_register(struct spi_nor *nor)
> > >  {
> > > -	struct dentry *rootdir, *d;
> > > +	static struct dentry *rootdir;
> > > +	struct dentry *d;
> > >  	int ret;
> > > 
> > >  	/* Create rootdir once. Will never be deleted again. */
> > > -	rootdir = debugfs_lookup(SPI_NOR_DEBUGFS_ROOT, NULL);
> > 
> > IIRC I had that one and it didn't work with spi-nor as a module.
> > Wouldn't it try to create the root dir twice if you remove the module
> > and load it again?
> 
> Yes it would, that is a use-model I did not consider at all, thanks.
> I'll rework this.

v2 with this fixed up now sent, thanks.

greg k-h