netdev - Re: [PATCH net-next 11/13] netlink: add net device refcount tracker to struct ethnl_req

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Message-ID: <CANn89iLYo8XQbKGxT=pKQepe8FeELx0pnpMWjKS8n93uHwNJ5Q@mail.gmail.com>
Date:   Tue, 4 Jan 2022 08:22:14 -0800
From:   Eric Dumazet <edumazet@...gle.com>
To:     Johannes Berg <johannes@...solutions.net>
Cc:     Eric Dumazet <eric.dumazet@...il.com>,
        "David S . Miller" <davem@...emloft.net>,
        Jakub Kicinski <kuba@...nel.org>,
        netdev <netdev@...r.kernel.org>
Subject: Re: [PATCH net-next 11/13] netlink: add net device refcount tracker
 to struct ethnl_req_info

On Tue, Jan 4, 2022 at 8:07 AM Johannes Berg <johannes@...solutions.net> wrote:
>
> Hi Eric,
>
> > > > @@ -624,6 +625,7 @@ static void ethnl_default_notify(struct net_device *dev, unsigned int cmd,
> > > >       }
> > > >
> > > >       req_info->dev = dev;
> > > > +     netdev_tracker_alloc(dev, &req_info->dev_tracker, GFP_KERNEL);
> > > >       req_info->flags |= ETHTOOL_FLAG_COMPACT_BITSETS;
> > > >
> > >
> > > I may have missed a follow-up patch (did a search on netdev now, but
> > > ...), but I'm hitting warnings from this and I'm not sure it's right?
> > >
> > > This req_info is just allocated briefly and freed again, and I'm not
> > > even sure there's a dev_get/dev_put involved here, I didn't see any?
> >
> > We had a fix.
> >
> > commit 34ac17ecbf575eb079094d44f1bd30c66897aa21
> > Author: Eric Dumazet <edumazet@...gle.com>
> > Date:   Tue Dec 14 00:42:30 2021 -0800
> >
> >     ethtool: use ethnl_parse_header_dev_put()
> >
>
> Hmm. I have this in my tree, and I don't think it affected
> ethnl_default_notify() anyway?

Strange, syzbot have not reported anything there.

ethnl_parse_header_dev_get() needs to take a ref, but
indeed ethnl_default_notify() does its own allocation/freeing.

diff --git a/net/ethtool/netlink.c b/net/ethtool/netlink.c
index ea23659fab28..5fe8f4ae2ceb 100644
--- a/net/ethtool/netlink.c
+++ b/net/ethtool/netlink.c
@@ -627,7 +627,6 @@ static void ethnl_default_notify(struct net_device
*dev, unsigned int cmd,
        }

        req_info->dev = dev;
-       netdev_tracker_alloc(dev, &req_info->dev_tracker, GFP_KERNEL);
        req_info->flags |= ETHTOOL_FLAG_COMPACT_BITSETS;

        ethnl_init_reply_data(reply_data, ops, dev);