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Fri, 11 Apr 2025 10:41:59 -0700 (PDT) Date: Fri, 11 Apr 2025 10:41:58 -0700 From: Stanislav Fomichev To: Jakub Kicinski Cc: sdf@fomichev.me, Kuniyuki Iwashima , andrew+netdev@lunn.ch, davem@davemloft.net, edumazet@google.com, horms@kernel.org, hramamurthy@google.com, jdamato@fastly.com, netdev@vger.kernel.org, pabeni@redhat.com Subject: Re: [PATCH net-next v2 6/8] netdev: depend on netdev->lock for xdp features Message-ID: References: <20250408195956.412733-7-kuba@kernel.org> <20250410171019.62128-1-kuniyu@amazon.com> <20250410191028.31a0eaf2@kernel.org> <20250410192326.0a5dbb10@kernel.org> Precedence: bulk X-Mailing-List: netdev@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline In-Reply-To: <20250410192326.0a5dbb10@kernel.org> On 04/10, Jakub Kicinski wrote: > On Thu, 10 Apr 2025 19:10:28 -0700 Jakub Kicinski wrote: > > On Thu, 10 Apr 2025 10:10:01 -0700 Kuniyuki Iwashima wrote: > > > syzkaller reported splats in register_netdevice() and > > > unregister_netdevice_many_notify(). > > > > > > In register_netdevice(), some devices cannot use > > > netdev_assert_locked(). > > > > > > In unregister_netdevice_many_notify(), maybe we need to > > > hold ops lock in UNREGISTER as you initially suggested. > > > Now do_setlink() deadlock does not happen. > > > > Ah... Thank you. > > > > Do you have a reference to use as Reported-by, or its from a > > non-public instance ? > > > > I'll test this shortly: > > > > diff --git a/net/core/netdev-genl.c b/net/core/netdev-genl.c > > index b64c614a00c4..891e2f60922f 100644 > > --- a/net/core/netdev-genl.c > > +++ b/net/core/netdev-genl.c > > @@ -38,7 +38,8 @@ netdev_nl_dev_fill(struct net_device *netdev, struct sk_buff *rsp, > > u64 xdp_rx_meta = 0; > > void *hdr; > > > > - netdev_assert_locked(netdev); /* note: rtnl_lock may not be held! */ > > + /* note: rtnl_lock may or may not be held! */ > > + netdev_assert_locked_or_invisible(netdev); > > > > hdr = genlmsg_iput(rsp, info); > > if (!hdr) > > @@ -966,7 +967,9 @@ static int netdev_genl_netdevice_event(struct notifier_block *nb, > > netdev_genl_dev_notify(netdev, NETDEV_CMD_DEV_ADD_NTF); > > break; > > case NETDEV_UNREGISTER: > > + netdev_lock(netdev); > > netdev_genl_dev_notify(netdev, NETDEV_CMD_DEV_DEL_NTF); > > + netdev_unlock(netdev); > > break; > > case NETDEV_XDP_FEAT_CHANGE: > > netdev_genl_dev_notify(netdev, NETDEV_CMD_DEV_CHANGE_NTF); > > Ugh, REGISTER is ops locked we'd need conditional locking here. > > Stanislav, I can make the REGISTERED notifier fully locked, right? > I suspect any new object we add that's protected by the instance > lock will want to lock the dev. Are you suggesting to do s/netdev_lock_ops/netdev_lock/ around call_netdevice_notifiers in register_netdevice? We can try, the biggest concern, as usual, are the stacking devices (with an extra lock), but casually grepping for NETDEV_REGISTER doesn't bring up anything suspicious. But if you're gonna do conditional locking for NETDEV_UNREGISTER, any reason not to play it safe and add conditional locking to NETDEV_REGISTER in netdev_genl_netdevice_event?