net_sched: sch_codel: implement lockless codel_dump()

Instead of relying on RTNL, codel_dump() can use READ_ONCE()
annotations, paired with WRITE_ONCE() ones in codel_change().

Signed-off-by: Eric Dumazet <edumazet@google.com>
Reviewed-by: Simon Horman <horms@kernel.org>
Signed-off-by: David S. Miller <davem@davemloft.net>

diff --git a/net/sched/sch_codel.c b/net/sched/sch_codel.c
index ecb3f16..3e8d4fe 100644 (file)
--- a/net/sched/sch_codel.c
+++ b/net/sched/sch_codel.c
@@ -118,26 +118,31 @@ static int codel_change(struct Qdisc *sch, struct nlattr *opt,
        if (tb[TCA_CODEL_TARGET]) {
                u32 target = nla_get_u32(tb[TCA_CODEL_TARGET]);
 
-               q->params.target = ((u64)target * NSEC_PER_USEC) >> CODEL_SHIFT;
+               WRITE_ONCE(q->params.target,
+                          ((u64)target * NSEC_PER_USEC) >> CODEL_SHIFT);
        }
 
        if (tb[TCA_CODEL_CE_THRESHOLD]) {
                u64 val = nla_get_u32(tb[TCA_CODEL_CE_THRESHOLD]);
 
-               q->params.ce_threshold = (val * NSEC_PER_USEC) >> CODEL_SHIFT;
+               WRITE_ONCE(q->params.ce_threshold,
+                          (val * NSEC_PER_USEC) >> CODEL_SHIFT);
        }
 
        if (tb[TCA_CODEL_INTERVAL]) {
                u32 interval = nla_get_u32(tb[TCA_CODEL_INTERVAL]);
 
-               q->params.interval = ((u64)interval * NSEC_PER_USEC) >> CODEL_SHIFT;
+               WRITE_ONCE(q->params.interval,
+                          ((u64)interval * NSEC_PER_USEC) >> CODEL_SHIFT);
        }
 
        if (tb[TCA_CODEL_LIMIT])
-               sch->limit = nla_get_u32(tb[TCA_CODEL_LIMIT]);
+               WRITE_ONCE(sch->limit,
+                          nla_get_u32(tb[TCA_CODEL_LIMIT]));
 
        if (tb[TCA_CODEL_ECN])
-               q->params.ecn = !!nla_get_u32(tb[TCA_CODEL_ECN]);
+               WRITE_ONCE(q->params.ecn,
+                          !!nla_get_u32(tb[TCA_CODEL_ECN]));
 
        qlen = sch->q.qlen;
        while (sch->q.qlen > sch->limit) {
@@ -183,6 +188,7 @@ static int codel_init(struct Qdisc *sch, struct nlattr *opt,
 static int codel_dump(struct Qdisc *sch, struct sk_buff *skb)
 {
        struct codel_sched_data *q = qdisc_priv(sch);
+       codel_time_t ce_threshold;
        struct nlattr *opts;
 
        opts = nla_nest_start_noflag(skb, TCA_OPTIONS);
@@ -190,17 +196,18 @@ static int codel_dump(struct Qdisc *sch, struct sk_buff *skb)
                goto nla_put_failure;
 
        if (nla_put_u32(skb, TCA_CODEL_TARGET,
-                       codel_time_to_us(q->params.target)) ||
+                       codel_time_to_us(READ_ONCE(q->params.target))) ||
            nla_put_u32(skb, TCA_CODEL_LIMIT,
-                       sch->limit) ||
+                       READ_ONCE(sch->limit)) ||
            nla_put_u32(skb, TCA_CODEL_INTERVAL,
-                       codel_time_to_us(q->params.interval)) ||
+                       codel_time_to_us(READ_ONCE(q->params.interval))) ||
            nla_put_u32(skb, TCA_CODEL_ECN,
-                       q->params.ecn))
+                       READ_ONCE(q->params.ecn)))
                goto nla_put_failure;
-       if (q->params.ce_threshold != CODEL_DISABLED_THRESHOLD &&
+       ce_threshold = READ_ONCE(q->params.ce_threshold);
+       if (ce_threshold != CODEL_DISABLED_THRESHOLD &&
            nla_put_u32(skb, TCA_CODEL_CE_THRESHOLD,
-                       codel_time_to_us(q->params.ce_threshold)))
+                       codel_time_to_us(ce_threshold)))
                goto nla_put_failure;
        return nla_nest_end(skb, opts);