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    SubjectRe: [PATCH 5.19 005/192] net: mvpp2: debugfs: fix memory leak when using debugfs_lookup()
    On Tue, Sep 13, 2022 at 05:48:58PM +0100, Russell King (Oracle) wrote:
    > On Tue, Sep 13, 2022 at 04:01:51PM +0200, Greg Kroah-Hartman wrote:
    > > From: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
    > >
    > > commit fe2c9c61f668cde28dac2b188028c5299cedcc1e upstream.
    > >
    > > 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: Marcin Wojtas <mw@semihalf.com>
    > > Cc: Russell King <linux@armlinux.org.uk>
    > > Cc: "David S. Miller" <davem@davemloft.net>
    > > Cc: Eric Dumazet <edumazet@google.com>
    > > Cc: Jakub Kicinski <kuba@kernel.org>
    > > Cc: Paolo Abeni <pabeni@redhat.com>
    > > Cc: netdev@vger.kernel.org
    > > Cc: stable <stable@kernel.org>
    > > Fixes: 21da57a23125 ("net: mvpp2: add a debugfs interface for the Header Parser")
    > > Signed-off-by: David S. Miller <davem@davemloft.net>
    > > Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
    > > ---
    > > drivers/net/ethernet/marvell/mvpp2/mvpp2_debugfs.c | 4 ++--
    > > 1 file changed, 2 insertions(+), 2 deletions(-)
    > >
    > > --- a/drivers/net/ethernet/marvell/mvpp2/mvpp2_debugfs.c
    > > +++ b/drivers/net/ethernet/marvell/mvpp2/mvpp2_debugfs.c
    > > @@ -700,10 +700,10 @@ void mvpp2_dbgfs_cleanup(struct mvpp2 *p
    > >
    > > void mvpp2_dbgfs_init(struct mvpp2 *priv, const char *name)
    > > {
    > > - struct dentry *mvpp2_dir, *mvpp2_root;
    > > + static struct dentry *mvpp2_root;
    > > + struct dentry *mvpp2_dir;
    > > int ret, i;
    > >
    > > - mvpp2_root = debugfs_lookup(MVPP2_DRIVER_NAME, NULL);
    > > if (!mvpp2_root)
    > > mvpp2_root = debugfs_create_dir(MVPP2_DRIVER_NAME, NULL);
    >
    > This looks broken to me.
    >
    > What happens if this is built as a module, and the module is loaded,
    > binds (and creates the directory), then is removed, and then re-
    > inserted? Nothing removes the old directory, so doesn't
    > debugfs_create_dir() fail, resulting in subsequent failure to add
    > any subsequent debugfs entries?
    >
    > I don't think this patch should be backported to stable trees until
    > this point is addressed.

    I'll drop this for now and get back to the fixup next week.

    thanks,

    greg k-h

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