From eb82a994479245a79647d302f9b4eb8e7c9d7ca6 Mon Sep 17 00:00:00 2001 From: John Fastabend Date: Sat, 24 Mar 2018 22:25:06 -0700 Subject: [PATCH] net: sched, fix OOO packets with pfifo_fast After the qdisc lock was dropped in pfifo_fast we allow multiple enqueue threads and dequeue threads to run in parallel. On the enqueue side the skb bit ooo_okay is used to ensure all related skbs are enqueued in-order. On the dequeue side though there is no similar logic. What we observe is with fewer queues than CPUs it is possible to re-order packets when two instances of __qdisc_run() are running in parallel. Each thread will dequeue a skb and then whichever thread calls the ndo op first will be sent on the wire. This doesn't typically happen because qdisc_run() is usually triggered by the same core that did the enqueue. However, drivers will trigger __netif_schedule() when queues are transitioning from stopped to awake using the netif_tx_wake_* APIs. When this happens netif_schedule() calls qdisc_run() on the same CPU that did the netif_tx_wake_* which is usually done in the interrupt completion context. This CPU is selected with the irq affinity which is unrelated to the enqueue operations. To resolve this we add a RUNNING bit to the qdisc to ensure only a single dequeue per qdisc is running. Enqueue and dequeue operations can still run in parallel and also on multi queue NICs we can still have a dequeue in-flight per qdisc, which is typically per CPU. Fixes: c5ad119fb6c0 ("net: sched: pfifo_fast use skb_array") Reported-by: Jakob Unterwurzacher Signed-off-by: John Fastabend Signed-off-by: David S. Miller --- include/net/sch_generic.h | 1 + net/sched/sch_generic.c | 19 ++++++++++++++----- 2 files changed, 15 insertions(+), 5 deletions(-) diff --git a/include/net/sch_generic.h b/include/net/sch_generic.h index 2092d33194dd..8da32678ce18 100644 --- a/include/net/sch_generic.h +++ b/include/net/sch_generic.h @@ -30,6 +30,7 @@ struct qdisc_rate_table { enum qdisc_state_t { __QDISC_STATE_SCHED, __QDISC_STATE_DEACTIVATED, + __QDISC_STATE_RUNNING, }; struct qdisc_size_table { diff --git a/net/sched/sch_generic.c b/net/sched/sch_generic.c index 7e3fbe9cc936..39c144b6ff98 100644 --- a/net/sched/sch_generic.c +++ b/net/sched/sch_generic.c @@ -373,24 +373,33 @@ bool sch_direct_xmit(struct sk_buff *skb, struct Qdisc *q, */ static inline bool qdisc_restart(struct Qdisc *q, int *packets) { + bool more, validate, nolock = q->flags & TCQ_F_NOLOCK; spinlock_t *root_lock = NULL; struct netdev_queue *txq; struct net_device *dev; struct sk_buff *skb; - bool validate; /* Dequeue packet */ - skb = dequeue_skb(q, &validate, packets); - if (unlikely(!skb)) + if (nolock && test_and_set_bit(__QDISC_STATE_RUNNING, &q->state)) return false; - if (!(q->flags & TCQ_F_NOLOCK)) + skb = dequeue_skb(q, &validate, packets); + if (unlikely(!skb)) { + if (nolock) + clear_bit(__QDISC_STATE_RUNNING, &q->state); + return false; + } + + if (!nolock) root_lock = qdisc_lock(q); dev = qdisc_dev(q); txq = skb_get_tx_queue(dev, skb); - return sch_direct_xmit(skb, q, dev, txq, root_lock, validate); + more = sch_direct_xmit(skb, q, dev, txq, root_lock, validate); + if (nolock) + clear_bit(__QDISC_STATE_RUNNING, &q->state); + return more; } void __qdisc_run(struct Qdisc *q)