net: openvswitch: pass NULL for unused parameters

From: Tom Rix <trix@redhat.com>

clang static analysis flags these problems

flow_table.c:713:2: warning: The expression is an uninitialized
  value. The computed value will also be garbage
        (*n_mask_hit)++;
        ^~~~~~~~~~~~~~~
flow_table.c:748:5: warning: The expression is an uninitialized
  value. The computed value will also be garbage
                                (*n_cache_hit)++;
                                ^~~~~~~~~~~~~~~~

These are not problems because neither pararmeter is used
by the calling function.

Looking at all of the calling functions, there are many
cases where the results are unused.  Passing unused
parameters is a waste.

To avoid passing unused parameters, rework the
masked_flow_lookup() and flow_lookup() routines to check
for NULL parameters and change the unused parameters to NULL.

Signed-off-by: Tom Rix <trix@redhat.com>
---
 net/openvswitch/flow_table.c | 16 +++++++---------
 1 file changed, 7 insertions(+), 9 deletions(-)

On Sun, Aug 30, 2020 at 6:17 PM <trix@redhat.com> wrote:
>
> From: Tom Rix <trix@redhat.com>
>
> clang static analysis flags these problems
>
> flow_table.c:713:2: warning: The expression is an uninitialized
>   value. The computed value will also be garbage
>         (*n_mask_hit)++;
>         ^~~~~~~~~~~~~~~
> flow_table.c:748:5: warning: The expression is an uninitialized
>   value. The computed value will also be garbage
>                                 (*n_cache_hit)++;
>                                 ^~~~~~~~~~~~~~~~
>
> These are not problems because neither pararmeter is used

parameter

> by the calling function.
>
> Looking at all of the calling functions, there are many
> cases where the results are unused.  Passing unused
> parameters is a waste.
>
> To avoid passing unused parameters, rework the
> masked_flow_lookup() and flow_lookup() routines to check
> for NULL parameters and change the unused parameters to NULL.
>
> Signed-off-by: Tom Rix <trix@redhat.com>
> ---
>  net/openvswitch/flow_table.c | 16 +++++++---------
>  1 file changed, 7 insertions(+), 9 deletions(-)
>
> diff --git a/net/openvswitch/flow_table.c b/net/openvswitch/flow_table.c
> index e2235849a57e..18e7fa3aa67e 100644
> --- a/net/openvswitch/flow_table.c
> +++ b/net/openvswitch/flow_table.c
> @@ -710,7 +710,8 @@ static struct sw_flow *masked_flow_lookup(struct table_instance *ti,
>         ovs_flow_mask_key(&masked_key, unmasked, false, mask);
>         hash = flow_hash(&masked_key, &mask->range);
>         head = find_bucket(ti, hash);
> -       (*n_mask_hit)++;
> +       if (n_mask_hit)
> +               (*n_mask_hit)++;
>
>         hlist_for_each_entry_rcu(flow, head, flow_table.node[ti->node_ver],
>                                 lockdep_ovsl_is_held()) {
> @@ -745,7 +746,8 @@ static struct sw_flow *flow_lookup(struct flow_table *tbl,
>                                 u64_stats_update_begin(&ma->syncp);
>                                 usage_counters[*index]++;
>                                 u64_stats_update_end(&ma->syncp);
> -                               (*n_cache_hit)++;
> +                               if (n_cache_hit)
> +                                       (*n_cache_hit)++;
>                                 return flow;
>                         }
>                 }
> @@ -798,9 +800,8 @@ struct sw_flow *ovs_flow_tbl_lookup_stats(struct flow_table *tbl,
>         *n_cache_hit = 0;

>         if (unlikely(!skb_hash || mc->cache_size == 0)) {
>                 u32 mask_index = 0;
> -               u32 cache = 0;
>
> -               return flow_lookup(tbl, ti, ma, key, n_mask_hit, &cache,
> +               return flow_lookup(tbl, ti, ma, key, n_mask_hit, NULL,
>                                    &mask_index);

Can it be done for mask_index as well?

>         }
>
> @@ -849,11 +850,9 @@ struct sw_flow *ovs_flow_tbl_lookup(struct flow_table *tbl,
>  {
>         struct table_instance *ti = rcu_dereference_ovsl(tbl->ti);
>         struct mask_array *ma = rcu_dereference_ovsl(tbl->mask_array);
> -       u32 __always_unused n_mask_hit;
> -       u32 __always_unused n_cache_hit;
>         u32 index = 0;
>

> -       return flow_lookup(tbl, ti, ma, key, &n_mask_hit, &n_cache_hit, &index);
> +       return flow_lookup(tbl, ti, ma, key, NULL, NULL, &index);

Ditto.

>  }
>
>  struct sw_flow *ovs_flow_tbl_lookup_exact(struct flow_table *tbl,
> @@ -865,7 +864,6 @@ struct sw_flow *ovs_flow_tbl_lookup_exact(struct flow_table *tbl,
>         /* Always called under ovs-mutex. */
>         for (i = 0; i < ma->max; i++) {
>                 struct table_instance *ti = rcu_dereference_ovsl(tbl->ti);
> -               u32 __always_unused n_mask_hit;
>                 struct sw_flow_mask *mask;
>                 struct sw_flow *flow;
>
> @@ -873,7 +871,7 @@ struct sw_flow *ovs_flow_tbl_lookup_exact(struct flow_table *tbl,
>                 if (!mask)
>                         continue;
>
> -               flow = masked_flow_lookup(ti, match->key, mask, &n_mask_hit);
> +               flow = masked_flow_lookup(ti, match->key, mask, NULL);
>                 if (flow && ovs_identifier_is_key(&flow->id) &&
>                     ovs_flow_cmp_unmasked_key(flow, match)) {
>                         return flow;
> --
> 2.18.1
>