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

[wang xiaolei]

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@xxxxxxxxxxxxx>
> > ---
> >   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