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Date:   Sun, 30 Aug 2020 13:32:18 -0700
From:   Tom Rix <trix@...hat.com>
To:     Andy Shevchenko <andy.shevchenko@...il.com>
Cc:     pshelar@....org, "David S. Miller" <davem@...emloft.net>,
        Jakub Kicinski <kuba@...nel.org>,
        Nathan Chancellor <natechancellor@...il.com>,
        Nick Desaulniers <ndesaulniers@...gle.com>,
        netdev <netdev@...r.kernel.org>, dev@...nvswitch.org,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] net: openvswitch: pass NULL for unused parameters


On 8/30/20 1:02 PM, Andy Shevchenko wrote:
> On Sun, Aug 30, 2020 at 6:17 PM <trix@...hat.com> wrote:
>> From: Tom Rix <trix@...hat.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
Too many ar's, it must be talk like a pirate day.
>
>> 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@...hat.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?

Yes, it's a bit more complicated but doable.

Tom

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