[PATCH net-next 0/2] net/sched: sch_drr: lockless cl->deficit and cl->quantum

[PATCH net-next 0/2] net/sched: sch_drr: lockless cl->deficit and cl->quantum

[Eric Dumazet]

First patch adds missing annotations around cl->deficit.

Second patch makes cl->quantum lockless, to prepare
future lockless qdisc dumps.

Eric Dumazet (2):
  net/sched: sch_drr: annotate data-races around cl->deficit
  net/sched: sch_drr: make cl->quantum lockless

 net/sched/sch_drr.c | 14 ++++++--------
 1 file changed, 6 insertions(+), 8 deletions(-)

-- 
2.54.0.563.g4f69b47b94-goog

[PATCH net-next 1/2] net/sched: sch_drr: annotate data-races around cl->deficit

[Eric Dumazet]

drr_dump_class_stats() runs without qdisc spinlock held.

Add missing READ_ONCE()/WRITE_ONCE() annotations around cl->deficit.

Fixes: edb09eb17ed8 ("net: sched: do not acquire qdisc spinlock in qdisc/class stats dump")
Signed-off-by: Eric Dumazet <edumazet@google.com>
---
 net/sched/sch_drr.c | 8 ++++----
 1 file changed, 4 insertions(+), 4 deletions(-)

diff --git a/net/sched/sch_drr.c b/net/sched/sch_drr.c
index 3f6687fa9666257952be5d44f9e3460845fe2a40..7da8c7c8421b7f2477c7c07d3b5920b375ce029e 100644
--- a/net/sched/sch_drr.c
+++ b/net/sched/sch_drr.c
@@ -270,7 +270,7 @@ static int drr_dump_class_stats(struct Qdisc *sch, unsigned long arg,
 
 	memset(&xstats, 0, sizeof(xstats));
 	if (qlen)
-		xstats.deficit = cl->deficit;
+		xstats.deficit = READ_ONCE(cl->deficit);
 
 	if (gnet_stats_copy_basic(d, NULL, &cl->bstats, true) < 0 ||
 	    gnet_stats_copy_rate_est(d, &cl->rate_est) < 0 ||
@@ -362,7 +362,7 @@ static int drr_enqueue(struct sk_buff *skb, struct Qdisc *sch,
 
 	if (!cl_is_active(cl)) {
 		list_add_tail(&cl->alist, &q->active);
-		cl->deficit = cl->quantum;
+		WRITE_ONCE(cl->deficit, cl->quantum);
 	}
 
 	qstats_backlog_add(sch, len);
@@ -389,7 +389,7 @@ static struct sk_buff *drr_dequeue(struct Qdisc *sch)
 
 		len = qdisc_pkt_len(skb);
 		if (len <= cl->deficit) {
-			cl->deficit -= len;
+			WRITE_ONCE(cl->deficit, cl->deficit - len);
 			skb = qdisc_dequeue_peeked(cl->qdisc);
 			if (unlikely(skb == NULL))
 				goto out;
@@ -403,7 +403,7 @@ static struct sk_buff *drr_dequeue(struct Qdisc *sch)
 			return skb;
 		}
 
-		cl->deficit += cl->quantum;
+		WRITE_ONCE(cl->deficit, cl->deficit + cl->quantum);
 		list_move_tail(&cl->alist, &q->active);
 	}
 out:
-- 
2.54.0.563.g4f69b47b94-goog

[PATCH net-next 2/2] net/sched: sch_drr: make cl->quantum lockless

[Eric Dumazet]

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

Signed-off-by: Eric Dumazet <edumazet@google.com>
---
 net/sched/sch_drr.c | 10 ++++------
 1 file changed, 4 insertions(+), 6 deletions(-)

diff --git a/net/sched/sch_drr.c b/net/sched/sch_drr.c
index 7da8c7c8421b7f2477c7c07d3b5920b375ce029e..020657f959b575667f7a4b4d6aacd05c03c654a0 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:
-- 
2.54.0.563.g4f69b47b94-goog