net: sched: Remove Qdisc::running sequence counter

The Qdisc::running sequence counter has two uses:

  1. Reliably reading qdisc's tc statistics while the qdisc is running
     (a seqcount read/retry loop at gnet_stats_add_basic()).

  2. As a flag, indicating whether the qdisc in question is running
     (without any retry loops).

For the first usage, the Qdisc::running sequence counter write section,
qdisc_run_begin() => qdisc_run_end(), covers a much wider area than what
is actually needed: the raw qdisc's bstats update. A u64_stats sync
point was thus introduced (in previous commits) inside the bstats
structure itself. A local u64_stats write section is then started and
stopped for the bstats updates.

Use that u64_stats sync point mechanism for the bstats read/retry loop
at gnet_stats_add_basic().

For the second qdisc->running usage, a __QDISC_STATE_RUNNING bit flag,
accessed with atomic bitops, is sufficient. Using a bit flag instead of
a sequence counter at qdisc_run_begin/end() and qdisc_is_running() leads
to the SMP barriers implicitly added through raw_read_seqcount() and
write_seqcount_begin/end() getting removed. All call sites have been
surveyed though, and no required ordering was identified.

Now that the qdisc->running sequence counter is no longer used, remove
it.

Note, using u64_stats implies no sequence counter protection for 64-bit
architectures. This can lead to the qdisc tc statistics "packets" vs.
"bytes" values getting out of sync on rare occasions. The individual
values will still be valid.

Signed-off-by: Ahmed S. Darwish <a.darwish@linutronix.de>
Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 7 insertions, 7 deletions

diff --git a/net/sched/sch_mqprio.c b/net/sched/sch_mqprio.c
index 3f7f756f92ca..b29f3453c6ea 100644
--- a/net/sched/sch_mqprio.c
+++ b/net/sched/sch_mqprio.c
@@ -402,8 +402,8 @@ static int mqprio_dump(struct Qdisc *sch, struct sk_buff *skb)
 		qdisc = netdev_get_tx_queue(dev, ntx)->qdisc_sleeping;
 		spin_lock_bh(qdisc_lock(qdisc));
 
-		gnet_stats_add_basic(NULL, &sch->bstats, qdisc->cpu_bstats,
-				     &qdisc->bstats);
+		gnet_stats_add_basic(&sch->bstats, qdisc->cpu_bstats,
+				     &qdisc->bstats, false);
 		gnet_stats_add_queue(&sch->qstats, qdisc->cpu_qstats,
 				     &qdisc->qstats);
 		sch->q.qlen += qdisc_qlen(qdisc);
@@ -519,8 +519,8 @@ static int mqprio_dump_class_stats(struct Qdisc *sch, unsigned long cl,
 
 			spin_lock_bh(qdisc_lock(qdisc));
 
-			gnet_stats_add_basic(NULL, &bstats, qdisc->cpu_bstats,
-					     &qdisc->bstats);
+			gnet_stats_add_basic(&bstats, qdisc->cpu_bstats,
+					     &qdisc->bstats, false);
 			gnet_stats_add_queue(&qstats, qdisc->cpu_qstats,
 					     &qdisc->qstats);
 			sch->q.qlen += qdisc_qlen(qdisc);
@@ -532,15 +532,15 @@ static int mqprio_dump_class_stats(struct Qdisc *sch, unsigned long cl,
 		/* Reclaim root sleeping lock before completing stats */
 		if (d->lock)
 			spin_lock_bh(d->lock);
-		if (gnet_stats_copy_basic(NULL, d, NULL, &bstats) < 0 ||
+		if (gnet_stats_copy_basic(d, NULL, &bstats, false) < 0 ||
 		    gnet_stats_copy_queue(d, NULL, &qstats, qlen) < 0)
 			return -1;
 	} else {
 		struct netdev_queue *dev_queue = mqprio_queue_get(sch, cl);
 
 		sch = dev_queue->qdisc_sleeping;
-		if (gnet_stats_copy_basic(qdisc_root_sleeping_running(sch), d,
-					  sch->cpu_bstats, &sch->bstats) < 0 ||
+		if (gnet_stats_copy_basic(d, sch->cpu_bstats,
+					  &sch->bstats, true) < 0 ||
 		    qdisc_qstats_copy(d, sch) < 0)
 			return -1;
 	}