Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 2620:137:e000::1:20 as permitted sender) client-ip=2620:137:e000::1:20;
Date:   Sat, 24 Sep 2022 10:46:22 +0200
From:   Greg Kroah-Hartman <gregkh@linuxfoundation.org>
To:     Michael Walle <michael@walle.cc>
Cc:     tudor.ambarus@microchip.com, pratyush@kernel.org,
        linux-kernel@vger.kernel.org,
        Miquel Raynal <miquel.raynal@bootlin.com>,
        Richard Weinberger <richard@nod.at>,
        Vignesh Raghavendra <vigneshr@ti.com>,
        linux-mtd@lists.infradead.org, stable <stable@kernel.org>
Subject: Re: [PATCH] mtd: spi-nor: fix memory leak when using debugfs_lookup()
Message-ID: <Yy7D3hmH9dYDUsdR@kroah.com>
References: <20220902133724.278133-1-gregkh@linuxfoundation.org>
 <bcd0cc5153457fb52566519a76e7b5b4@walle.cc>
MIME-Version: 1.0
Content-Type: text/plain; charset=us-ascii
Content-Disposition: inline
In-Reply-To: <bcd0cc5153457fb52566519a76e7b5b4@walle.cc>
Precedence: bulk

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@microchip.com>
> > Cc: Pratyush Yadav <pratyush@kernel.org>
> > Cc: Michael Walle <michael@walle.cc>
> > Cc: Miquel Raynal <miquel.raynal@bootlin.com>
> > Cc: Richard Weinberger <richard@nod.at>
> > Cc: Vignesh Raghavendra <vigneshr@ti.com>
> > Cc: linux-mtd@lists.infradead.org
> > Cc: stable <stable@kernel.org>
> > Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.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.

greg k-h