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Date: Fri, 18 Mar 2022 16:45:33 +0100
From: Niels Dossche <dossche.niels@...il.com>
To: Paolo Abeni <pabeni@...hat.com>, netdev@...r.kernel.org
Cc: "David S. Miller" <davem@...emloft.net>,
Hideaki YOSHIFUJI <yoshfuji@...ux-ipv6.org>,
David Ahern <dsahern@...nel.org>,
Jakub Kicinski <kuba@...nel.org>
Subject: Re: [PATCH v2] ipv6: acquire write lock for addr_list in
dev_forward_change
On 18/03/2022 16:42, Paolo Abeni wrote:
> 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 <dossche.niels@...il.com>
>>>> ---
>>>>
>>>> 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
>
I see, nice small change.
Only thing I notice is that list_for_each_entry_rcu should be used instead of list_for_each_entry inside the rcu lock, right?
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