Subject: Re: [PATCH net-next] net: sched: set dedicated tcf_walker flag when tp is empty

From: Vlad Buslov <[email-masked]>
Date: Tue, 26 Feb 2019 15:08:45 +0000

On Mon 25 Feb 2019 at 22:52, Cong Wang <[email-masked]> wrote:
> On Mon, Feb 25, 2019 at 7:38 AM Vlad Buslov <[email-masked]> wrote:
>>
>> Using tcf_walker->stop flag to determine when tcf_walker->fn() was called
>> at least once is unreliable. Some classifiers set 'stop' flag on error
>> before calling walker callback, other classifiers used to call it with NULL
>> filter pointer when empty. In order to prevent further regressions, extend
>> tcf_walker structure with dedicated 'nonempty' flag. Set this flag in
>> tcf_walker->fn() implementation that is used to check if classifier has
>> filters configured.
>
>
> So, after this patch commits like 31a998487641 ("net: sched: fw: don't
> set arg->stop in fw_walk() when empty") can be reverted??

Yes, it is safe now to revert following commits:

3027ff41f67c ("net: sched: route: don't set arg->stop in route4_walk() when empty")
31a998487641 ("net: sched: fw: don't set arg->stop in fw_walk() when empty")

>
>
>>
>> Fixes: 8b64678e0af8 ("net: sched: refactor tp insert/delete for concurrent execution")
>> Signed-off-by: Vlad Buslov <[email-masked]>
>> Suggested-by: Cong Wang <[email-masked]>
>> ---
>>  include/net/pkt_cls.h |  1 +
>>  net/sched/cls_api.c   | 13 +++++++++----
>>  2 files changed, 10 insertions(+), 4 deletions(-)
>>
>> diff --git a/include/net/pkt_cls.h b/include/net/pkt_cls.h
>> index 232f801f2a21..422dd8800478 100644
>> --- a/include/net/pkt_cls.h
>> +++ b/include/net/pkt_cls.h
>> @@ -17,6 +17,7 @@ struct tcf_walker {
>>         int     stop;
>>         int     skip;
>>         int     count;
>> +       bool    nonempty;
>>         unsigned long cookie;
>>         int     (*fn)(struct tcf_proto *, void *node, struct tcf_walker *);
>>  };
>> diff --git a/net/sched/cls_api.c b/net/sched/cls_api.c
>> index e2c888961379..3543be31d400 100644
>> --- a/net/sched/cls_api.c
>> +++ b/net/sched/cls_api.c
>> @@ -238,18 +238,23 @@ static void tcf_proto_put(struct tcf_proto *tp, bool rtnl_held,
>>                 tcf_proto_destroy(tp, rtnl_held, extack);
>>  }
>>
>> -static int walker_noop(struct tcf_proto *tp, void *d, struct tcf_walker *arg)
>> +static int walker_check_empty(struct tcf_proto *tp, void *d,
>> +                             struct tcf_walker *arg)
>>  {
>> -       return -1;
>> +       if (tp) {
>> +               arg->nonempty = true;
>> +               return -1;
>> +       }
>> +       return 0;
>
> How does this even work? If we can simply check tp!=NULL as
> non-empty, why do we even need a walker??
>
> For me, it must be pushed down to each implementation to
> determine how it is empty.

Sorry, this is a typo. Intention is to check the filter pointer (void
*d). Sending the fix.

Thanks for spotting this!