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

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Message-ID: <bcd0cc5153457fb52566519a76e7b5b4@walle.cc>
Date:   Fri, 02 Sep 2022 16:01:36 +0200
From:   Michael Walle <michael@...le.cc>
To:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>
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()

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?

-michael

>  	if (!rootdir)
>  		rootdir = debugfs_create_dir(SPI_NOR_DEBUGFS_ROOT, NULL);