Re: hard-coded limit on unresolved multicast route cache in ipv4/ipmr.c causes slow, unreliable creation of multicast routes on busy networks

On Mon, Nov 26, 2018 at 10:44:49AM +0530, Sukumar Gopalakrishnan wrote:

Hi,

 There is a patch to make this queue len configurable. Is below mentioned going
to be applied ?

http://lkml.iu.edu/hypermail/linux/kernel/1810.3/02344.html

It looks this topic stuckd again..

Regards,
Sukumar

On Tue, Nov 20, 2018 at 2:55 PM Hangbin Liu [off-list ref] wrote:

    Hi David,

    On Sat, Jul 21, 2018 at 10:03:09PM -0700, David Miller wrote:
    > Yeah that limit is bogus for several reasons.
    ...
    >
    > Therefore, it probably is safe and correct to remove this
    > cache_resolve_queue_len altogether.
    >
    > Something like this:
    >
    > diff --git a/include/linux/mroute_base.h b/include/linux/mroute_base.h
    > index d633f737b3c6..b166465d7c05 100644
    > --- a/include/linux/mroute_base.h
    > +++ b/include/linux/mroute_base.h
    > @@ -234,7 +234,6 @@ struct mr_table_ops {
    >   * @mfc_hash: Hash table of all resolved routes for easy lookup
    >   * @mfc_cache_list: list of resovled routes for possible traversal
    >   * @maxvif: Identifier of highest value vif currently in use
    > - * @cache_resolve_queue_len: current size of unresolved queue
    >   * @mroute_do_assert: Whether to inform userspace on wrong ingress
    >   * @mroute_do_pim: Whether to receive IGMP PIMv1
    >   * @mroute_reg_vif_num: PIM-device vif index
    > @@ -251,7 +250,6 @@ struct mr_table {
    >       struct rhltable         mfc_hash;
    >       struct list_head        mfc_cache_list;
    >       int                     maxvif;
    > -     atomic_t                cache_resolve_queue_len;
    >       bool                    mroute_do_assert;
    >       bool                    mroute_do_pim;
    >       int                     mroute_reg_vif_num;
    > diff --git a/net/ipv4/ipmr.c b/net/ipv4/ipmr.c
    > index 9f79b9803a16..c007cf9bfe82 100644
    > --- a/net/ipv4/ipmr.c
    > +++ b/net/ipv4/ipmr.c
    > @@ -747,8 +747,6 @@ static void ipmr_destroy_unres(struct mr_table *mrt,
    struct mfc_cache *c)
    >       struct sk_buff *skb;
    >       struct nlmsgerr *e;
    > 
    > -     atomic_dec(&mrt->cache_resolve_queue_len);
    > -
    >       while ((skb = skb_dequeue(&c->_c.mfc_un.unres.unresolved))) {
    >               if (ip_hdr(skb)->version == 0) {
    >                       struct nlmsghdr *nlh = skb_pull(skb,
    > @@ -1135,9 +1133,11 @@ static int ipmr_cache_unresolved(struct mr_table
    *mrt, vifi_t vifi,
    >       }
    > 
    >       if (!found) {
    > +             bool was_empty;
    > +
    >               /* Create a new entry if allowable */
    > -             if (atomic_read(&mrt->cache_resolve_queue_len) >= 10 ||
    > -                 (c = ipmr_cache_alloc_unres()) == NULL) {
    > +             c = ipmr_cache_alloc_unres();
    > +             if (!c) {
    >                       spin_unlock_bh(&mfc_unres_lock);
    > 
    >                       kfree_skb(skb);
    > @@ -1163,11 +1163,11 @@ static int ipmr_cache_unresolved(struct mr_table
    *mrt, vifi_t vifi,
    >                       return err;
    >               }
    > 
    > -             atomic_inc(&mrt->cache_resolve_queue_len);
    > +             was_empty = list_empty(&mrt->mfc_unres_queue);
    >               list_add(&c->_c.list, &mrt->mfc_unres_queue);
    >               mroute_netlink_event(mrt, c, RTM_NEWROUTE);
    > 
    > -             if (atomic_read(&mrt->cache_resolve_queue_len) == 1)
    > +             if (was_empty)
    >                       mod_timer(&mrt->ipmr_expire_timer,
    >                                 c->_c.mfc_un.unres.expires);

    In ipmr_expire_process() and ipmr_do_expire_process(), they start mod_timer
    when !list_empty(&mrt->mfc_unres_queue), should here also be !was_empty?

    BTW, do you have any plan to apply this patch in kernel?

    Regards
    Hangbin

    >       }
    > @@ -1274,7 +1274,6 @@ static int ipmr_mfc_add(struct net *net, struct
    mr_table *mrt,
    >               if (uc->mfc_origin == c->mfc_origin &&
    >                   uc->mfc_mcastgrp == c->mfc_mcastgrp) {
    >                       list_del(&_uc->list);
    > -                     atomic_dec(&mrt->cache_resolve_queue_len);
    >                       found = true;
    >                       break;
    >               }
    > @@ -1322,7 +1321,7 @@ static void mroute_clean_tables(struct mr_table
    *mrt, bool all)
    >               mr_cache_put(c);
    >       }
    > 
    > -     if (atomic_read(&mrt->cache_resolve_queue_len) != 0) {
    > +     if (!list_empty(&mrt->mfc_unres_queue)) {
    >               spin_lock_bh(&mfc_unres_lock);
    >               list_for_each_entry_safe(c, tmp, &mrt->mfc_unres_queue,
    list) {
    >                       list_del(&c->list);
    > @@ -2648,9 +2647,19 @@ static int ipmr_rtm_route(struct sk_buff *skb,
    struct nlmsghdr *nlh,
    >               return ipmr_mfc_delete(tbl, &mfcc, parent);
    >  }
    > 
    > +static int queue_count(struct mr_table *mrt)
    > +{
    > +     struct list_head *pos;
    > +     int count = 0;
    > +     
    > +     list_for_each(pos, &mrt->mfc_unres_queue)
    > +             count++;
    > +     return count;
    > +}
    > +
    >  static bool ipmr_fill_table(struct mr_table *mrt, struct sk_buff *skb)
    >  {
    > -     u32 queue_len = atomic_read(&mrt->cache_resolve_queue_len);
    > +     u32 queue_len = queue_count(mrt);
    > 
    >       if (nla_put_u32(skb, IPMRA_TABLE_ID, mrt->id) ||
    >           nla_put_u32(skb, IPMRA_TABLE_CACHE_RES_QUEUE_LEN, queue_len) ||
    > diff --git a/net/ipv6/ip6mr.c b/net/ipv6/ip6mr.c
    > index 0d0f0053bb11..75e9c5a3e7ea 100644
    > --- a/net/ipv6/ip6mr.c
    > +++ b/net/ipv6/ip6mr.c
    > @@ -759,8 +759,6 @@ static void ip6mr_destroy_unres(struct mr_table *mrt,
    struct mfc6_cache *c)
    >       struct net *net = read_pnet(&mrt->net);
    >       struct sk_buff *skb;
    > 
    > -     atomic_dec(&mrt->cache_resolve_queue_len);
    > -
    >       while ((skb = skb_dequeue(&c->_c.mfc_un.unres.unresolved)) != NULL)
    {
    >               if (ipv6_hdr(skb)->version == 0) {
    >                       struct nlmsghdr *nlh = skb_pull(skb,
    > @@ -1139,8 +1137,8 @@ static int ip6mr_cache_unresolved(struct mr_table
    *mrt, mifi_t mifi,
    >                *      Create a new entry if allowable
    >                */
    > 
    > -             if (atomic_read(&mrt->cache_resolve_queue_len) >= 10 ||
    > -                 (c = ip6mr_cache_alloc_unres()) == NULL) {
    > +             c = ip6mr_cache_alloc_unres();
    > +             if (!c) {
    >                       spin_unlock_bh(&mfc_unres_lock);
    > 
    >                       kfree_skb(skb);
    > @@ -1167,7 +1165,6 @@ static int ip6mr_cache_unresolved(struct mr_table
    *mrt, mifi_t mifi,
    >                       return err;
    >               }
    > 
    > -             atomic_inc(&mrt->cache_resolve_queue_len);
    >               list_add(&c->_c.list, &mrt->mfc_unres_queue);
    >               mr6_netlink_event(mrt, c, RTM_NEWROUTE);
    > 
    > @@ -1455,7 +1452,6 @@ static int ip6mr_mfc_add(struct net *net, struct
    mr_table *mrt,
    >               if (ipv6_addr_equal(&uc->mf6c_origin, &c->mf6c_origin) &&
    >                   ipv6_addr_equal(&uc->mf6c_mcastgrp, &c->mf6c_mcastgrp))
    {
    >                       list_del(&_uc->list);
    > -                     atomic_dec(&mrt->cache_resolve_queue_len);
    >                       found = true;
    >                       break;
    >               }
    > @@ -1502,7 +1498,7 @@ static void mroute_clean_tables(struct mr_table
    *mrt, bool all)
    >               mr_cache_put(c);
    >       }
    > 
    > -     if (atomic_read(&mrt->cache_resolve_queue_len) != 0) {
    > +     if (!list_empty(&mrt->mfc_unres_queue)) {
    >               spin_lock_bh(&mfc_unres_lock);
    >               list_for_each_entry_safe(c, tmp, &mrt->mfc_unres_queue,
    list) {
    >                       list_del(&c->list);