Re: [net PATCH] net/sched: Get stab before calling ops->change()

[wang xiaolei <xiaolei.wang@windriver.com>]

On 5/10/24 11:19 PM, Simon Horman wrote:
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> On Thu, May 09, 2024 at 10:40:43AM +0800, Xiaolei Wang wrote:
>> ops->change() depends on stab, there is such a situation
>> When no parameters are passed in for the first time, stab
>> is omitted, as in configuration 1 below. At this time, a
>> warning "Warning: sch_taprio: Size table not specified, frame
>> length estimates may be inaccurate" will be received. When
>> stab is added for the second time, parameters, like configuration
>> 2 below, because the stab is still empty when ops->change()
>> is running, you will also receive the above warning.
>>
>> 1. tc qdisc replace dev eth1 parent root handle 100 taprio \
>>    num_tc 5 map 0 1 2 3 4 queues 1@0 1@1 1@2 1@3 1@4 base-time 0 \
>>    sched-entry S 1 100000 \
>>    sched-entry S 2 100000 \
>>    sched-entry S 4 100000 \
>>    max-sdu 0 0 0 0 0 0 0 200 \
>>    flags 2
>>
>>    2. tc qdisc replace dev eth1 parent root overhead 24 handle 100 taprio \
>>    num_tc 5 map 0 1 2 3 4 queues 1@0 1@1 1@2 1@3 1@4 base-time 0 \
>>    sched-entry S 1 100000 \
>>    sched-entry S 2 100000 \
>>    sched-entry S 4 100000 \
>>    max-sdu 0 0 0 0 0 0 0 200 \
>>    flags 2
>>
> Hi Xiaolei Wang,
>
> If this is a fix, targeted at the net tree, then it should probably have
> a Fixes tag here (no blank line between it and other tags).
>
>> Signed-off-by: Xiaolei Wang <xiaolei.wang@windriver.com>
>> ---
>>   net/sched/sch_api.c | 20 ++++++++++----------
>>   1 file changed, 10 insertions(+), 10 deletions(-)
>>
>> diff --git a/net/sched/sch_api.c b/net/sched/sch_api.c
>> index 60239378d43f..fec358f497d5 100644
>> --- a/net/sched/sch_api.c
>> +++ b/net/sched/sch_api.c
>> @@ -1404,6 +1404,16 @@ static int qdisc_change(struct Qdisc *sch, struct nlattr **tca,
>>        struct qdisc_size_table *ostab, *stab = NULL;
>>        int err = 0;
>>
>> +     if (tca[TCA_STAB]) {
>> +             stab = qdisc_get_stab(tca[TCA_STAB], extack);
>> +             if (IS_ERR(stab))
>> +                     return PTR_ERR(stab);
>> +     }
>> +
>> +     ostab = rtnl_dereference(sch->stab);
>> +     rcu_assign_pointer(sch->stab, stab);
>> +     qdisc_put_stab(ostab);
>> +
>>        if (tca[TCA_OPTIONS]) {
>>                if (!sch->ops->change) {
>>                        NL_SET_ERR_MSG(extack, "Change operation not supported by specified qdisc");
> I am concerned that in this case the stab will be updated even if the
> change operation is rejected by the following code in the if
> (tca[TCA_OPTIONS]) block, just below the above hunk.
>
>                  if (tca[TCA_INGRESS_BLOCK] || tca[TCA_EGRESS_BLOCK]) {
>                          NL_SET_ERR_MSG(extack, "Change of blocks is not supported");
>                          return -EOPNOTSUPP;
>                  }
> ...

Well, that makes sense, I will research further

thanks

xiaolei

>
> --
> pw-bot: under-review