net_sched: sch_cbs: implement lockless cbs_dump()

Instead of relying on RTNL, cbs_dump() can use READ_ONCE()
annotations, paired with WRITE_ONCE() ones in cbs_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>

net/sched/sch_cbs.c

@@ -389,11 +389,11 @@ static int cbs_change(struct Qdisc *sch, struct nlattr *opt,
 	}
 
 	/* Everything went OK, save the parameters used. */
-	q->hicredit = qopt->hicredit;
-	q->locredit = qopt->locredit;
-	q->idleslope = qopt->idleslope * BYTES_PER_KBIT;
-	q->sendslope = qopt->sendslope * BYTES_PER_KBIT;
-	q->offload = qopt->offload;
+	WRITE_ONCE(q->hicredit, qopt->hicredit);
+	WRITE_ONCE(q->locredit, qopt->locredit);
+	WRITE_ONCE(q->idleslope, qopt->idleslope * BYTES_PER_KBIT);
+	WRITE_ONCE(q->sendslope, qopt->sendslope * BYTES_PER_KBIT);
+	WRITE_ONCE(q->offload, qopt->offload);
 
 	return 0;
 }
@@ -459,11 +459,11 @@ static int cbs_dump(struct Qdisc *sch, struct sk_buff *skb)
 	if (!nest)
 		goto nla_put_failure;
 
-	opt.hicredit = q->hicredit;
-	opt.locredit = q->locredit;
-	opt.sendslope = div64_s64(q->sendslope, BYTES_PER_KBIT);
-	opt.idleslope = div64_s64(q->idleslope, BYTES_PER_KBIT);
-	opt.offload = q->offload;
+	opt.hicredit = READ_ONCE(q->hicredit);
+	opt.locredit = READ_ONCE(q->locredit);
+	opt.sendslope = div64_s64(READ_ONCE(q->sendslope), BYTES_PER_KBIT);
+	opt.idleslope = div64_s64(READ_ONCE(q->idleslope), BYTES_PER_KBIT);
+	opt.offload = READ_ONCE(q->offload);
 
 	if (nla_put(skb, TCA_CBS_PARMS, sizeof(opt), &opt))
 		goto nla_put_failure;