[PATCH 5.12 244/296] net: sched: fix tx action reschedule issue with stopped queue

Greg Kroah-Hartman
2021-05-31T16:46:10Z

From: Yunsheng Lin <linyunsheng@huawei.com>

[ Upstream commit dcad9ee9e0663d74a89b25b987f9c7be86432812 ]

The netdev qeueue might be stopped when byte queue limit has
reached or tx hw ring is full, net_tx_action() may still be
rescheduled if STATE_MISSED is set, which consumes unnecessary
cpu without dequeuing and transmiting any skb because the
netdev queue is stopped, see qdisc_run_end().

This patch fixes it by checking the netdev queue state before
calling qdisc_run() and clearing STATE_MISSED if netdev queue is
stopped during qdisc_run(), the net_tx_action() is rescheduled
again when netdev qeueue is restarted, see netif_tx_wake_queue().

As there is time window between netif_xmit_frozen_or_stopped()
checking and STATE_MISSED clearing, between which STATE_MISSED
may set by net_tx_action() scheduled by netif_tx_wake_queue(),
so set the STATE_MISSED again if netdev queue is restarted.

Fixes: 6b3ba9146fe6 ("net: sched: allow qdiscs to handle locking")
Reported-by: Michal Kubecek <mkubecek@suse.cz>
Acked-by: Jakub Kicinski <kuba@kernel.org>
Signed-off-by: Yunsheng Lin <linyunsheng@huawei.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
net/core/dev.c | 3 ++-
net/sched/sch_generic.c | 27 ++++++++++++++++++++++++++-
2 files changed, 28 insertions(+), 2 deletions(-)

diff --git a/net/core/dev.c b/net/core/dev.c
index 30c911357582..963194474058 100644
--- a/net/core/dev.c
+++ b/net/core/dev.c
@@ -3804,7 +3804,8 @@ static inline int __dev_xmit_skb(struct sk_buff *skb, struct Qdisc *q,

if (q->flags & TCQ_F_NOLOCK) {
rc = q->enqueue(skb, q, &to_free) & NET_XMIT_MASK;
- qdisc_run(q);
+ if (likely(!netif_xmit_frozen_or_stopped(txq)))
+ qdisc_run(q);

if (unlikely(to_free))
kfree_skb_list(to_free);
diff --git a/net/sched/sch_generic.c b/net/sched/sch_generic.c
index e6844d3567ca..854d2b38db85 100644
--- a/net/sched/sch_generic.c
+++ b/net/sched/sch_generic.c
@@ -35,6 +35,25 @@
const struct Qdisc_ops *default_qdisc_ops = &pfifo_fast_ops;
EXPORT_SYMBOL(default_qdisc_ops);

+static void qdisc_maybe_clear_missed(struct Qdisc *q,
+ const struct netdev_queue *txq)
+{
+ clear_bit(__QDISC_STATE_MISSED, &q->state);
+
+ /* Make sure the below netif_xmit_frozen_or_stopped()
+ * checking happens after clearing STATE_MISSED.
+ */
+ smp_mb__after_atomic();
+
+ /* Checking netif_xmit_frozen_or_stopped() again to
+ * make sure STATE_MISSED is set if the STATE_MISSED
+ * set by netif_tx_wake_queue()'s rescheduling of
+ * net_tx_action() is cleared by the above clear_bit().
+ */
+ if (!netif_xmit_frozen_or_stopped(txq))
+ set_bit(__QDISC_STATE_MISSED, &q->state);
+}
+
/* Main transmission queue. */

/* Modifications to data participating in scheduling must be protected with
@@ -74,6 +93,7 @@ static inline struct sk_buff *__skb_dequeue_bad_txq(struct Qdisc *q)
}
} else {
skb = SKB_XOFF_MAGIC;
+ qdisc_maybe_clear_missed(q, txq);
}
}

@@ -242,6 +262,7 @@ static struct sk_buff *dequeue_skb(struct Qdisc *q, bool *validate,
}
} else {
skb = NULL;
+ qdisc_maybe_clear_missed(q, txq);
}
if (lock)
spin_unlock(lock);
@@ -251,8 +272,10 @@ validate:
*validate = true;

if ((q->flags & TCQ_F_ONETXQUEUE) &&
- netif_xmit_frozen_or_stopped(txq))
+ netif_xmit_frozen_or_stopped(txq)) {
+ qdisc_maybe_clear_missed(q, txq);
return skb;
+ }

skb = qdisc_dequeue_skb_bad_txq(q);
if (unlikely(skb)) {
@@ -311,6 +334,8 @@ bool sch_direct_xmit(struct sk_buff *skb, struct Qdisc *q,
HARD_TX_LOCK(dev, txq, smp_processor_id());
if (!netif_xmit_frozen_or_stopped(txq))
skb = dev_hard_start_xmit(skb, dev, txq, &ret);
+ else
+ qdisc_maybe_clear_missed(q, txq);

HARD_TX_UNLOCK(dev, txq);
} else {
--
2.30.2