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

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Message-ID: <20210126100257.GN3565223@nanopsycho.orion>
Date:   Tue, 26 Jan 2021 11:02:57 +0100
From:   Jiri Pirko <jiri@...nulli.us>
To:     Ivan Vecera <ivecera@...hat.com>
Cc:     netdev@...r.kernel.org, "David S . Miller" <davem@...emloft.net>,
        Cong Wang <xiyou.wangcong@...il.com>,
        Jakub Kicinski <kuba@...nel.org>,
        Saeed Mahameed <saeed@...nel.org>
Subject: Re: [PATCH net] team: protect features update by RCU to avoid
 deadlock

Mon, Jan 25, 2021 at 08:44:16AM CET, 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.
>
>Fixes: 3d249d4ca7d0 ("net: introduce ethernet teaming device")
>Cc: Jiri Pirko <jiri@...nulli.us>
>Cc: David S. Miller <davem@...emloft.net>
>Cc: Cong Wang <xiyou.wangcong@...il.com>
>Cc: Jakub Kicinski <kuba@...nel.org>
>Cc: Saeed Mahameed <saeed@...nel.org>
>Signed-off-by: Ivan Vecera <ivecera@...hat.com>

Reviewed-by: Jiri Pirko <jiri@...dia.com>