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[146.241.232.135]) by smtp.gmail.com with ESMTPSA id g6-20020adfd1e6000000b00203f8effc22sm2242020wrd.63.2022.03.18.08.42.43 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Fri, 18 Mar 2022 08:42:43 -0700 (PDT) Message-ID: <13558e3e0ed23097f04bb90b43c261062dca9107.camel@redhat.com> Subject: Re: [PATCH v2] ipv6: acquire write lock for addr_list in dev_forward_change From: Paolo Abeni To: Niels Dossche , netdev@vger.kernel.org Cc: "David S. Miller" , Hideaki YOSHIFUJI , David Ahern , Jakub Kicinski Date: Fri, 18 Mar 2022 16:42:42 +0100 In-Reply-To: References: <20220317155637.29733-1-dossche.niels@gmail.com> <7bd311d0846269f331a1d401c493f5511491d0df.camel@redhat.com> Content-Type: text/plain; charset="UTF-8" User-Agent: Evolution 3.42.4 (3.42.4-1.fc35) MIME-Version: 1.0 Content-Transfer-Encoding: 7bit Precedence: bulk List-ID: X-Mailing-List: netdev@vger.kernel.org On Fri, 2022-03-18 at 13:48 +0100, Paolo Abeni wrote: > On Fri, 2022-03-18 at 10:13 +0100, Paolo Abeni wrote: > > On Thu, 2022-03-17 at 16:56 +0100, Niels Dossche wrote: > > > No path towards dev_forward_change (common ancestor of paths is in > > > addrconf_fixup_forwarding) acquires idev->lock for idev->addr_list. > > > We need to hold the lock during the whole loop in dev_forward_change. > > > __ipv6_dev_ac_{inc,dec} both acquire the write lock on idev->lock in > > > their function body. Since addrconf_{join,leave}_anycast call to > > > __ipv6_dev_ac_inc and __ipv6_dev_ac_dec respectively, we need to move > > > the responsibility of locking upwards. > > > > > > This patch moves the locking up. For __ipv6_dev_ac_dec, there is one > > > place where the caller can directly acquire the idev->lock, that is in > > > ipv6_dev_ac_dec. The other caller is addrconf_leave_anycast, which now > > > needs to be called under idev->lock, and thus it becomes the > > > responsibility of the callers of addrconf_leave_anycast to hold that > > > lock. For __ipv6_dev_ac_inc, there are also 2 callers, one is > > > ipv6_sock_ac_join, which can acquire the lock during the call to > > > __ipv6_dev_ac_inc. The other caller is addrconf_join_anycast, which now > > > needs to be called under idev->lock, and thus it becomes the > > > responsibility of the callers of addrconf_join_anycast to hold that > > > lock. > > > > > > Signed-off-by: Niels Dossche > > > --- > > > > > > Changes in v2: > > > - Move the locking upwards > > > > > > net/ipv6/addrconf.c | 21 ++++++++++++++++----- > > > net/ipv6/anycast.c | 37 ++++++++++++++++--------------------- > > > 2 files changed, 32 insertions(+), 26 deletions(-) > > > > > > diff --git a/net/ipv6/addrconf.c b/net/ipv6/addrconf.c > > > index f908e2fd30b2..69e9f81e2045 100644 > > > --- a/net/ipv6/addrconf.c > > > +++ b/net/ipv6/addrconf.c > > > @@ -818,6 +818,7 @@ static void dev_forward_change(struct inet6_dev *idev) > > > } > > > } > > > > > > + write_lock_bh(&idev->lock); > > > list_for_each_entry(ifa, &idev->addr_list, if_list) { > > > if (ifa->flags&IFA_F_TENTATIVE) > > > continue; > > > @@ -826,6 +827,7 @@ static void dev_forward_change(struct inet6_dev *idev) > > > else > > > addrconf_leave_anycast(ifa); > > > } > > > + write_unlock_bh(&idev->lock); > > > inet6_netconf_notify_devconf(dev_net(dev), RTM_NEWNETCONF, > > > NETCONFA_FORWARDING, > > > dev->ifindex, &idev->cnf); > > > @@ -2191,7 +2193,7 @@ void addrconf_leave_solict(struct inet6_dev *idev, const struct in6_addr *addr) > > > __ipv6_dev_mc_dec(idev, &maddr); > > > } > > > > > > -/* caller must hold RTNL */ > > > +/* caller must hold RTNL and write lock idev->lock */ > > > static void addrconf_join_anycast(struct inet6_ifaddr *ifp) > > > { > > > struct in6_addr addr; > > > @@ -2204,7 +2206,7 @@ static void addrconf_join_anycast(struct inet6_ifaddr *ifp) > > > __ipv6_dev_ac_inc(ifp->idev, &addr); > > > } > > > > > > -/* caller must hold RTNL */ > > > +/* caller must hold RTNL and write lock idev->lock */ > > > static void addrconf_leave_anycast(struct inet6_ifaddr *ifp) > > > { > > > struct in6_addr addr; > > > @@ -3857,8 +3859,11 @@ static int addrconf_ifdown(struct net_device *dev, bool unregister) > > > __ipv6_ifa_notify(RTM_DELADDR, ifa); > > > inet6addr_notifier_call_chain(NETDEV_DOWN, ifa); > > > } else { > > > - if (idev->cnf.forwarding) > > > + if (idev->cnf.forwarding) { > > > + write_lock_bh(&idev->lock); > > > addrconf_leave_anycast(ifa); > > > + write_unlock_bh(&idev->lock); > > > + } > > > addrconf_leave_solict(ifa->idev, &ifa->addr); > > > } > > > > > > @@ -6136,16 +6141,22 @@ static void __ipv6_ifa_notify(int event, struct inet6_ifaddr *ifp) > > > &ifp->addr, ifp->idev->dev->name); > > > } > > > > > > - if (ifp->idev->cnf.forwarding) > > > + if (ifp->idev->cnf.forwarding) { > > > + write_lock_bh(&ifp->idev->lock); > > > addrconf_join_anycast(ifp); > > > + write_unlock_bh(&ifp->idev->lock); > > > + } > > > if (!ipv6_addr_any(&ifp->peer_addr)) > > > addrconf_prefix_route(&ifp->peer_addr, 128, > > > ifp->rt_priority, ifp->idev->dev, > > > 0, 0, GFP_ATOMIC); > > > break; > > > case RTM_DELADDR: > > > - if (ifp->idev->cnf.forwarding) > > > + if (ifp->idev->cnf.forwarding) { > > > + write_lock_bh(&ifp->idev->lock); > > > addrconf_leave_anycast(ifp); > > > + write_unlock_bh(&ifp->idev->lock); > > > + } > > > addrconf_leave_solict(ifp->idev, &ifp->addr); > > > if (!ipv6_addr_any(&ifp->peer_addr)) { > > > struct fib6_info *rt; > > > diff --git a/net/ipv6/anycast.c b/net/ipv6/anycast.c > > > index dacdea7fcb62..f3017ed6f005 100644 > > > --- a/net/ipv6/anycast.c > > > +++ b/net/ipv6/anycast.c > > > @@ -136,7 +136,9 @@ int ipv6_sock_ac_join(struct sock *sk, int ifindex, const struct in6_addr *addr) > > > goto error; > > > } > > > > > > + write_lock_bh(&idev->lock); > > > err = __ipv6_dev_ac_inc(idev, addr); > > > + write_unlock_bh(&idev->lock); > > > > I feat this is problematic, due this call chain: > > > > __ipv6_dev_ac_inc() -> addrconf_join_solict() -> ipv6_dev_mc_inc -> > > __ipv6_dev_mc_inc -> mutex_lock(&idev->mc_lock); > > > > The latter call requires process context. > > > > One alternarive (likely very hackish way) to solve this could be: > > - adding another list entry into struct inet6_dev, rtnl protected. > > Typo above: the new field should be added to 'struct inet6_ifaddr'. > > > - traverse addr_list under idev->lock and add each entry with > > forwarding on to into a tmp list (e.g. tmp_join) using the field above; > > add the entries with forwarding off into another tmp list (e.g. > > tmp_leave), still using the same field. > > Again confusing text above, sorry. As the forwarding flag is per > device, all the addr entries will land into the same tmp list. > > It's probably better if I sketch up some code... For the records, I mean something alongside the following - completely not tested: --- diff --git a/include/net/if_inet6.h b/include/net/if_inet6.h index 4cfdef6ca4f6..2df3c98b9e55 100644 --- a/include/net/if_inet6.h +++ b/include/net/if_inet6.h @@ -64,6 +64,7 @@ struct inet6_ifaddr { struct hlist_node addr_lst; struct list_head if_list; + struct list_head if_list_aux; struct list_head tmp_list; struct inet6_ifaddr *ifpub; diff --git a/net/ipv6/addrconf.c b/net/ipv6/addrconf.c index b22504176588..27d1081b693e 100644 --- a/net/ipv6/addrconf.c +++ b/net/ipv6/addrconf.c @@ -797,6 +797,7 @@ static void dev_forward_change(struct inet6_dev *idev) { struct net_device *dev; struct inet6_ifaddr *ifa; + LIST_HEAD(tmp); if (!idev) return; @@ -815,9 +816,17 @@ static void dev_forward_change(struct inet6_dev *idev) } } + rcu_read_lock(); list_for_each_entry(ifa, &idev->addr_list, if_list) { if (ifa->flags&IFA_F_TENTATIVE) continue; + list_add_tail(&ifa->if_list_aux, &tmp); + } + rcu_read_unlock(); + + while (!list_empty(&tmp)) { + ifa = list_first_entry(&tmp, struct inet6_ifaddr, if_list_aux); + list_del(&ifa->if_list_aux); if (idev->cnf.forwarding) addrconf_join_anycast(ifa); else