[ovs-dev] [branch-2.1 branch-2.0 PATCH] datapath: Fix a bug.

Pravin Shelar pshelar at nicira.com
Mon Jun 30 19:00:00 UTC 2014


Good catch.


On Mon, Jun 30, 2014 at 10:59 AM, Alex Wang <alexw at nicira.com> wrote:
> Due to the race condition in userspace, there is chance that two
> overlapping megaflows could be installed in datapath.  And this
> causes userspace unable to delete the less inclusive megaflow flow
> even after it timeout, since the flow_del logic will stop at the
> first match of masked flow.
>
> This commit fixes the bug by making the kernel flow_del logic check
> all masks in that case.
>
> Signed-off-by: Alex Wang <alexw at nicira.com>
Can you also give specific subject for this patch?

> ---
>  datapath/datapath.c   |    4 ++--
>  datapath/flow_table.c |   16 ++++++++++++++++
>  datapath/flow_table.h |    3 +++
>  3 files changed, 21 insertions(+), 2 deletions(-)
>
> diff --git a/datapath/datapath.c b/datapath/datapath.c
> index c15ded9..cb66ff3 100644
> --- a/datapath/datapath.c
> +++ b/datapath/datapath.c
> @@ -974,8 +974,8 @@ static int ovs_flow_cmd_del(struct sk_buff *skb, struct genl_info *info)
>         if (err)
>                 goto unlock;
>
> -       flow = ovs_flow_tbl_lookup(&dp->table, &key);
> -       if (!flow || !ovs_flow_cmp_unmasked_key(flow, &match)) {
> +       flow = ovs_flow_tbl_lookup_exact(&dp->table, &key, &match);

match has ref to key, so you can just pass match as argument to this function.

> +       if (!flow) {
>                 err = -ENOENT;
>                 goto unlock;
>         }

> diff --git a/datapath/flow_table.c b/datapath/flow_table.c
> index fa7ad36..a0d1ea7 100644
> --- a/datapath/flow_table.c
> +++ b/datapath/flow_table.c
> @@ -482,6 +482,22 @@ struct sw_flow *ovs_flow_tbl_lookup(struct flow_table *tbl,
>         return ovs_flow_tbl_lookup_stats(tbl, key, &n_mask_hit);
>  }
>
> +struct sw_flow *ovs_flow_tbl_lookup_exact(struct flow_table *tbl,
> +                                         const struct sw_flow_key *key,
> +                                         struct sw_flow_match *match)
> +{
> +       struct table_instance *ti = rcu_dereference_ovsl(tbl->ti);
> +       struct sw_flow_mask *mask;
> +       struct sw_flow *flow;
> +
> +       list_for_each_entry_rcu(mask, &tbl->mask_list, list) {
> +               flow = masked_flow_lookup(ti, key, mask);
> +               if (flow && ovs_flow_cmp_unmasked_key(flow, match))  /* Found */
> +                       return flow;
> +       }
This function is always called under ovs-mutex, so no need to use rcu iterator.

> +       return NULL;
> +}
> +
>  int ovs_flow_tbl_num_masks(const struct flow_table *table)
>  {
>         struct sw_flow_mask *mask;
> diff --git a/datapath/flow_table.h b/datapath/flow_table.h
> index baaeb10..3697427 100644
> --- a/datapath/flow_table.h
> +++ b/datapath/flow_table.h
> @@ -72,6 +72,9 @@ struct sw_flow *ovs_flow_tbl_dump_next(struct table_instance *table,
>  struct sw_flow *ovs_flow_tbl_lookup_stats(struct flow_table *,
>                                     const struct sw_flow_key *,
>                                     u32 *n_mask_hit);
> +struct sw_flow *ovs_flow_tbl_lookup_exact(struct flow_table *tbl,
> +                                         const struct sw_flow_key *key,
> +                                         struct sw_flow_match *match);

We should use same exact-lookup for flow_get and when we try to modify flow.

>  struct sw_flow *ovs_flow_tbl_lookup(struct flow_table *,
>                                     const struct sw_flow_key *);
>
> --
> 1.7.9.5
>



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