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authorJohn Fastabend <john.fastabend@gmail.com>2018-03-24 22:25:06 -0700
committerDavid S. Miller <davem@davemloft.net>2018-03-26 12:36:23 -0400
commiteb82a994479245a79647d302f9b4eb8e7c9d7ca6 (patch)
treef2b46c8bc079ea5f443c9ecbd082e053b39c0f42 /net/sched
parent743989254ea9f132517806d8893ca9b6cf9dc86b (diff)
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 <jakob.unterwurzacher@theobroma-systems.com> Signed-off-by: John Fastabend <john.fastabend@gmail.com> Signed-off-by: David S. Miller <davem@davemloft.net>
Diffstat (limited to 'net/sched')
-rw-r--r--net/sched/sch_generic.c17
1 files changed, 13 insertions, 4 deletions
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 */
+ if (nolock && test_and_set_bit(__QDISC_STATE_RUNNING, &q->state))
+ return false;
+
skb = dequeue_skb(q, &validate, packets);
- if (unlikely(!skb))
+ if (unlikely(!skb)) {
+ if (nolock)
+ clear_bit(__QDISC_STATE_RUNNING, &q->state);
return false;
+ }
- if (!(q->flags & TCQ_F_NOLOCK))
+ 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)