netdev - Re: [PATCH net] team: protect features update by RCU to avoid deadlock

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Date:   Tue, 26 Jan 2021 07:36:12 +0100
From:   Ivan Vecera <ivecera@...hat.com>
To:     Cong Wang <xiyou.wangcong@...il.com>
Cc:     Linux Kernel Network Developers <netdev@...r.kernel.org>,
        Jiri Pirko <jiri@...nulli.us>,
        "David S . Miller" <davem@...emloft.net>,
        Jakub Kicinski <kuba@...nel.org>,
        Saeed Mahameed <saeed@...nel.org>
Subject: Re: [PATCH net] team: protect features update by RCU to avoid
 deadlock

On Mon, 25 Jan 2021 12:53:22 -0800
Cong Wang <xiyou.wangcong@...il.com> wrote:

> On Sun, Jan 24, 2021 at 11:44 PM Ivan Vecera <ivecera@...hat.com> wrote:
> >
> > Function __team_compute_features() is protected by team->lock
> > mutex when it is called from team_compute_features() used when
> > features of an underlying device is changed. This causes
> > a deadlock when NETDEV_FEAT_CHANGE notifier for underlying device
> > is fired due to change propagated from team driver (e.g. MTU
> > change). It's because callbacks like team_change_mtu() or
> > team_vlan_rx_{add,del}_vid() protect their port list traversal
> > by team->lock mutex.
> >
> > Example (r8169 case where this driver disables TSO for certain MTU
> > values):
> > ...
> > [ 6391.348202]  __mutex_lock.isra.6+0x2d0/0x4a0
> > [ 6391.358602]  team_device_event+0x9d/0x160 [team]
> > [ 6391.363756]  notifier_call_chain+0x47/0x70
> > [ 6391.368329]  netdev_update_features+0x56/0x60
> > [ 6391.373207]  rtl8169_change_mtu+0x14/0x50 [r8169]
> > [ 6391.378457]  dev_set_mtu_ext+0xe1/0x1d0
> > [ 6391.387022]  dev_set_mtu+0x52/0x90
> > [ 6391.390820]  team_change_mtu+0x64/0xf0 [team]
> > [ 6391.395683]  dev_set_mtu_ext+0xe1/0x1d0
> > [ 6391.399963]  do_setlink+0x231/0xf50
> > ...
> >
> > In fact team_compute_features() called from team_device_event()
> > does not need to be protected by team->lock mutex and rcu_read_lock()
> > is sufficient there for port list traversal.  
> 
> Reviewed-by: Cong Wang <xiyou.wangcong@...il.com>
> 
> In the future, please version your patch so that we can easily
> find out which is the latest.

OK, got it... I haven't added a version due to different subjects...

Thanks,
Ivan