From: Eric Dumazet <edumazet@google.com>
Date: Tue, 19 May 2026 09:46:18 +0000 (+0000)
Subject: net/sched: sch_drr: make cl->quantum lockless
X-Git-Url: http://git.ipfire.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=a4d880b85089e12a5f2e8e2fee386310cec5b99a;p=thirdparty%2Flinux.git

net/sched: sch_drr: make cl->quantum lockless

cl->quantum does not need to be protected by RTNL or qdisc spinlock.

Signed-off-by: Eric Dumazet <edumazet@google.com>
Link: https://patch.msgid.link/20260519094618.2632073-3-edumazet@google.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
---

diff --git a/net/sched/sch_drr.c b/net/sched/sch_drr.c
index 7da8c7c8421b..020657f959b5 100644
--- a/net/sched/sch_drr.c
+++ b/net/sched/sch_drr.c
@@ -97,10 +97,8 @@ static int drr_change_class(struct Qdisc *sch, u32 classid, u32 parentid,
 			}
 		}
 
-		sch_tree_lock(sch);
 		if (tb[TCA_DRR_QUANTUM])
-			cl->quantum = quantum;
-		sch_tree_unlock(sch);
+			WRITE_ONCE(cl->quantum, quantum);
 
 		return 0;
 	}
@@ -251,7 +249,7 @@ static int drr_dump_class(struct Qdisc *sch, unsigned long arg,
 	nest = nla_nest_start_noflag(skb, TCA_OPTIONS);
 	if (nest == NULL)
 		goto nla_put_failure;
-	if (nla_put_u32(skb, TCA_DRR_QUANTUM, cl->quantum))
+	if (nla_put_u32(skb, TCA_DRR_QUANTUM, READ_ONCE(cl->quantum)))
 		goto nla_put_failure;
 	return nla_nest_end(skb, nest);
 
@@ -362,7 +360,7 @@ static int drr_enqueue(struct sk_buff *skb, struct Qdisc *sch,
 
 	if (!cl_is_active(cl)) {
 		list_add_tail(&cl->alist, &q->active);
-		WRITE_ONCE(cl->deficit, cl->quantum);
+		WRITE_ONCE(cl->deficit, READ_ONCE(cl->quantum));
 	}
 
 	qstats_backlog_add(sch, len);
@@ -403,7 +401,7 @@ static struct sk_buff *drr_dequeue(struct Qdisc *sch)
 			return skb;
 		}
 
-		WRITE_ONCE(cl->deficit, cl->deficit + cl->quantum);
+		WRITE_ONCE(cl->deficit, cl->deficit + READ_ONCE(cl->quantum));
 		list_move_tail(&cl->alist, &q->active);
 	}
 out: