| Message ID | 20240415132054.3822230-5-edumazet@google.com (mailing list archive) |
|---|---|
| State | Superseded |
| Delegated to: | Netdev Maintainers |
| Headers | show |
| Series | net_sched: first series for RTNL-less qdisc dumps | expand |
On Mon, Apr 15, 2024 at 01:20:44PM +0000, Eric Dumazet wrote: > Instead of relying on RTNL, choke_dump() can use READ_ONCE() > annotations, paired with WRITE_ONCE() ones in choke_change(). > > Also use READ_ONCE(q->limit) in choke_enqueue() as the value > could change from choke_change(). Hi Eric, I'm wondering if you could expand on why q->limit needs this treatment but not other fields, f.e. q->parms.qth_min (aka p->qth_min). > Signed-off-by: Eric Dumazet <edumazet@google.com> > --- > include/net/red.h | 10 +++++----- > net/sched/sch_choke.c | 23 ++++++++++++----------- > 2 files changed, 17 insertions(+), 16 deletions(-) > > diff --git a/include/net/red.h b/include/net/red.h ... > @@ -244,7 +244,7 @@ static inline void red_set_parms(struct red_parms *p, > max_P = red_maxp(Plog); > max_P *= delta; /* max_P = (qth_max - qth_min)/2^Plog */ > } > - p->max_P = max_P; > + WRITE_ONCE(p->max_P, max_P); > max_p_delta = max_P / delta; > max_p_delta = max(max_p_delta, 1U); > p->max_P_reciprocal = reciprocal_value(max_p_delta); A little further down in this function p->Scell_log is set. I think it also needs the WRITE_ONCE() treatment as it is read in choke_dump(). > diff --git a/net/sched/sch_choke.c b/net/sched/sch_choke.c ... > @@ -431,15 +431,16 @@ static int choke_init(struct Qdisc *sch, struct nlattr *opt, > static int choke_dump(struct Qdisc *sch, struct sk_buff *skb) > { > struct choke_sched_data *q = qdisc_priv(sch); > + u8 Wlog = READ_ONCE(q->parms.Wlog); > struct nlattr *opts = NULL; > struct tc_red_qopt opt = { > - .limit = q->limit, > - .flags = q->flags, > - .qth_min = q->parms.qth_min >> q->parms.Wlog, > - .qth_max = q->parms.qth_max >> q->parms.Wlog, > - .Wlog = q->parms.Wlog, > - .Plog = q->parms.Plog, > - .Scell_log = q->parms.Scell_log, > + .limit = READ_ONCE(q->limit), > + .flags = READ_ONCE(q->flags), > + .qth_min = READ_ONCE(q->parms.qth_min) >> Wlog, > + .qth_max = READ_ONCE(q->parms.qth_max) >> Wlog, > + .Wlog = Wlog, > + .Plog = READ_ONCE(q->parms.Plog), > + .Scell_log = READ_ONCE(q->parms.Scell_log), > }; > > opts = nla_nest_start_noflag(skb, TCA_OPTIONS);
On Wed, Apr 17, 2024 at 3:14 PM Simon Horman <horms@kernel.org> wrote: > > On Mon, Apr 15, 2024 at 01:20:44PM +0000, Eric Dumazet wrote: > > Instead of relying on RTNL, choke_dump() can use READ_ONCE() > > annotations, paired with WRITE_ONCE() ones in choke_change(). > > > > Also use READ_ONCE(q->limit) in choke_enqueue() as the value > > could change from choke_change(). > > Hi Eric, > > I'm wondering if you could expand on why q->limit needs this treatment > but not other fields, f.e. q->parms.qth_min (aka p->qth_min). Other fields got their WRITE_ONCE() in red_set_parms() + WRITE_ONCE(p->qth_min, qth_min << Wlog); + WRITE_ONCE(p->qth_max, qth_max << Wlog); + WRITE_ONCE(p->Wlog, Wlog); + WRITE_ONCE(p->Plog, Plog); > > > Signed-off-by: Eric Dumazet <edumazet@google.com> > > --- > > include/net/red.h | 10 +++++----- > > net/sched/sch_choke.c | 23 ++++++++++++----------- > > 2 files changed, 17 insertions(+), 16 deletions(-) > > > > diff --git a/include/net/red.h b/include/net/red.h > > ... > > > @@ -244,7 +244,7 @@ static inline void red_set_parms(struct red_parms *p, > > max_P = red_maxp(Plog); > > max_P *= delta; /* max_P = (qth_max - qth_min)/2^Plog */ > > } > > - p->max_P = max_P; > > + WRITE_ONCE(p->max_P, max_P); > > max_p_delta = max_P / delta; > > max_p_delta = max(max_p_delta, 1U); > > p->max_P_reciprocal = reciprocal_value(max_p_delta); > > A little further down in this function p->Scell_log is set. > I think it also needs the WRITE_ONCE() treatment as it > is read in choke_dump(). > I will squash in v2 the missing WRITE_ONCE(), thanks ! diff --git a/include/net/red.h b/include/net/red.h index 7daf7cf6130aeccf3d81a77600f4445759f174b7..802287d52c9e37e76ba9154539f511629e4b9780 100644 --- a/include/net/red.h +++ b/include/net/red.h @@ -257,7 +257,7 @@ static inline void red_set_parms(struct red_parms *p, p->target_min = qth_min + 2*delta; p->target_max = qth_min + 3*delta; - p->Scell_log = Scell_log; + WRITE_ONCE(p->Scell_log, Scell_log); p->Scell_max = (255 << Scell_log); if (stab)
On Wed, Apr 17, 2024 at 03:41:36PM +0200, Eric Dumazet wrote: > On Wed, Apr 17, 2024 at 3:14 PM Simon Horman <horms@kernel.org> wrote: > > > > On Mon, Apr 15, 2024 at 01:20:44PM +0000, Eric Dumazet wrote: > > > Instead of relying on RTNL, choke_dump() can use READ_ONCE() > > > annotations, paired with WRITE_ONCE() ones in choke_change(). > > > > > > Also use READ_ONCE(q->limit) in choke_enqueue() as the value > > > could change from choke_change(). > > > > Hi Eric, > > > > I'm wondering if you could expand on why q->limit needs this treatment > > but not other fields, f.e. q->parms.qth_min (aka p->qth_min). > > Other fields got their WRITE_ONCE() in red_set_parms() > > + WRITE_ONCE(p->qth_min, qth_min << Wlog); > + WRITE_ONCE(p->qth_max, qth_max << Wlog); > + WRITE_ONCE(p->Wlog, Wlog); > + WRITE_ONCE(p->Plog, Plog); Thanks, understood. I do wonder if other schedulers may need WRITE_ONCE() in their enqueue() function. But I have not analysed this yet. > > > Signed-off-by: Eric Dumazet <edumazet@google.com> > > > --- > > > include/net/red.h | 10 +++++----- > > > net/sched/sch_choke.c | 23 ++++++++++++----------- > > > 2 files changed, 17 insertions(+), 16 deletions(-) > > > > > > diff --git a/include/net/red.h b/include/net/red.h > > > > ... > > > > > @@ -244,7 +244,7 @@ static inline void red_set_parms(struct red_parms *p, > > > max_P = red_maxp(Plog); > > > max_P *= delta; /* max_P = (qth_max - qth_min)/2^Plog */ > > > } > > > - p->max_P = max_P; > > > + WRITE_ONCE(p->max_P, max_P); > > > max_p_delta = max_P / delta; > > > max_p_delta = max(max_p_delta, 1U); > > > p->max_P_reciprocal = reciprocal_value(max_p_delta); > > > > A little further down in this function p->Scell_log is set. > > I think it also needs the WRITE_ONCE() treatment as it > > is read in choke_dump(). > > > > I will squash in v2 the missing WRITE_ONCE(), thanks ! Likewise, thanks. Your proposed update looks good to me. > diff --git a/include/net/red.h b/include/net/red.h > index 7daf7cf6130aeccf3d81a77600f4445759f174b7..802287d52c9e37e76ba9154539f511629e4b9780 > 100644 > --- a/include/net/red.h > +++ b/include/net/red.h > @@ -257,7 +257,7 @@ static inline void red_set_parms(struct red_parms *p, > p->target_min = qth_min + 2*delta; > p->target_max = qth_min + 3*delta; > > - p->Scell_log = Scell_log; > + WRITE_ONCE(p->Scell_log, Scell_log); > p->Scell_max = (255 << Scell_log); > > if (stab) >
diff --git a/include/net/red.h b/include/net/red.h index 425364de0df7913cdd6361a0eb8d18b418372787..7daf7cf6130aeccf3d81a77600f4445759f174b7 100644 --- a/include/net/red.h +++ b/include/net/red.h @@ -233,10 +233,10 @@ static inline void red_set_parms(struct red_parms *p, int delta = qth_max - qth_min; u32 max_p_delta; - p->qth_min = qth_min << Wlog; - p->qth_max = qth_max << Wlog; - p->Wlog = Wlog; - p->Plog = Plog; + WRITE_ONCE(p->qth_min, qth_min << Wlog); + WRITE_ONCE(p->qth_max, qth_max << Wlog); + WRITE_ONCE(p->Wlog, Wlog); + WRITE_ONCE(p->Plog, Plog); if (delta <= 0) delta = 1; p->qth_delta = delta; @@ -244,7 +244,7 @@ static inline void red_set_parms(struct red_parms *p, max_P = red_maxp(Plog); max_P *= delta; /* max_P = (qth_max - qth_min)/2^Plog */ } - p->max_P = max_P; + WRITE_ONCE(p->max_P, max_P); max_p_delta = max_P / delta; max_p_delta = max(max_p_delta, 1U); p->max_P_reciprocal = reciprocal_value(max_p_delta); diff --git a/net/sched/sch_choke.c b/net/sched/sch_choke.c index ea108030c6b410418f0b58ba7ea51e1b524d4df9..51e68c9661727e64862392a76880bed5fa0c27a2 100644 --- a/net/sched/sch_choke.c +++ b/net/sched/sch_choke.c @@ -264,7 +264,7 @@ static int choke_enqueue(struct sk_buff *skb, struct Qdisc *sch, } /* Admit new packet */ - if (sch->q.qlen < q->limit) { + if (sch->q.qlen < READ_ONCE(q->limit)) { q->tab[q->tail] = skb; q->tail = (q->tail + 1) & q->tab_mask; ++sch->q.qlen; @@ -405,8 +405,8 @@ static int choke_change(struct Qdisc *sch, struct nlattr *opt, } else sch_tree_lock(sch); - q->flags = ctl->flags; - q->limit = ctl->limit; + WRITE_ONCE(q->flags, ctl->flags); + WRITE_ONCE(q->limit, ctl->limit); red_set_parms(&q->parms, ctl->qth_min, ctl->qth_max, ctl->Wlog, ctl->Plog, ctl->Scell_log, @@ -431,15 +431,16 @@ static int choke_init(struct Qdisc *sch, struct nlattr *opt, static int choke_dump(struct Qdisc *sch, struct sk_buff *skb) { struct choke_sched_data *q = qdisc_priv(sch); + u8 Wlog = READ_ONCE(q->parms.Wlog); struct nlattr *opts = NULL; struct tc_red_qopt opt = { - .limit = q->limit, - .flags = q->flags, - .qth_min = q->parms.qth_min >> q->parms.Wlog, - .qth_max = q->parms.qth_max >> q->parms.Wlog, - .Wlog = q->parms.Wlog, - .Plog = q->parms.Plog, - .Scell_log = q->parms.Scell_log, + .limit = READ_ONCE(q->limit), + .flags = READ_ONCE(q->flags), + .qth_min = READ_ONCE(q->parms.qth_min) >> Wlog, + .qth_max = READ_ONCE(q->parms.qth_max) >> Wlog, + .Wlog = Wlog, + .Plog = READ_ONCE(q->parms.Plog), + .Scell_log = READ_ONCE(q->parms.Scell_log), }; opts = nla_nest_start_noflag(skb, TCA_OPTIONS); @@ -447,7 +448,7 @@ static int choke_dump(struct Qdisc *sch, struct sk_buff *skb) goto nla_put_failure; if (nla_put(skb, TCA_CHOKE_PARMS, sizeof(opt), &opt) || - nla_put_u32(skb, TCA_CHOKE_MAX_P, q->parms.max_P)) + nla_put_u32(skb, TCA_CHOKE_MAX_P, READ_ONCE(q->parms.max_P))) goto nla_put_failure; return nla_nest_end(skb, opts);
Instead of relying on RTNL, choke_dump() can use READ_ONCE() annotations, paired with WRITE_ONCE() ones in choke_change(). Also use READ_ONCE(q->limit) in choke_enqueue() as the value could change from choke_change(). Signed-off-by: Eric Dumazet <edumazet@google.com> --- include/net/red.h | 10 +++++----- net/sched/sch_choke.c | 23 ++++++++++++----------- 2 files changed, 17 insertions(+), 16 deletions(-)