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Miller" , Jonathan Toppins , Paolo Abeni , Eric Dumazet , Liang Li , Simon Horman , Miroslav Lichvar Subject: Re: [PATCHv4 net-next] bonding: add software tx timestamping support In-reply-to: <20230414180205.1220135d@kernel.org> References: <20230414083526.1984362-1-liuhangbin@gmail.com> <20230414180205.1220135d@kernel.org> Comments: In-reply-to Jakub Kicinski message dated "Fri, 14 Apr 2023 18:02:05 -0700." X-Mailer: MH-E 8.6+git; nmh 1.6; Emacs 29.0.50 MIME-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-ID: <6104.1681530194.1@famine> Content-Transfer-Encoding: quoted-printable Date: Fri, 14 Apr 2023 20:43:14 -0700 Message-ID: <6105.1681530194@famine> Precedence: bulk List-ID: X-Mailing-List: netdev@vger.kernel.org Jakub Kicinski wrote: >On Fri, 14 Apr 2023 16:35:26 +0800 Hangbin Liu wrote: >> v4: add ASSERT_RTNL to make sure bond_ethtool_get_ts_info() called via >> RTNL. Only check _TX_SOFTWARE for the slaves. > >> + ASSERT_RTNL(); >> + >> rcu_read_lock(); >> real_dev =3D bond_option_active_slave_get_rcu(bond); >> dev_hold(real_dev); >> @@ -5707,10 +5713,36 @@ static int bond_ethtool_get_ts_info(struct net_= device *bond_dev, >> ret =3D ops->get_ts_info(real_dev, info); >> goto out; >> } >> + } else { >> + /* Check if all slaves support software tx timestamping */ >> + rcu_read_lock(); >> + bond_for_each_slave_rcu(bond, slave, iter) { > >> + ret =3D -1; >> + ops =3D slave->dev->ethtool_ops; >> + phydev =3D slave->dev->phydev; >> + >> + if (phy_has_tsinfo(phydev)) >> + ret =3D phy_ts_info(phydev, &ts_info); >> + else if (ops->get_ts_info) >> + ret =3D ops->get_ts_info(slave->dev, &ts_info); > >My comment about this path being under rtnl was to point out that we >don't need the RCU protection to iterate over the slaves. This is = >a bit of a guess, I don't know bonding, but can we not use >bond_for_each_slave() ? Ah, I missed that nuance. And, yes, you're correct, bond_for_each_slave() works with RTNL and we don't need RCU here if RTNL is held. >As a general rule we should let all driver callbacks sleep. Drivers = >may need to consult the FW or read something over a slow asynchronous >bus which requires process / non-atomic context. RCU lock puts us in = >an atomic context. And ->get_ts_info() is a driver callback. Agreed. >It's not a deal breaker if we can't avoid RCU, but if we can - we should >let the drivers sleep. Sorry if I wasn't very clear previously. Understood; I should have remembered this, as it's been an issue arising from the "in the middle" aspect of bonding in the past. -J --- -Jay Vosburgh, jay.vosburgh@canonical.com