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authorYunsheng Lin <linyunsheng@huawei.com>2021-05-14 11:17:00 +0800
committerDavid S. Miller <davem@davemloft.net>2021-05-14 15:05:46 -0700
commit102b55ee92f9fda4dde7a45d2b20538e6e3e3d1e (patch)
treeb99ff14fdb63b9a505bab2d45f01289a925424a5 /net
parenta90c57f2cedd52a511f739fb55e6244e22e1a2fb (diff)
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net: sched: fix tx action rescheduling issue during deactivation
Currently qdisc_run() checks the STATE_DEACTIVATED of lockless qdisc before calling __qdisc_run(), which ultimately clear the STATE_MISSED when all the skb is dequeued. If STATE_DEACTIVATED is set before clearing STATE_MISSED, there may be rescheduling of net_tx_action() at the end of qdisc_run_end(), see below: CPU0(net_tx_atcion) CPU1(__dev_xmit_skb) CPU2(dev_deactivate) . . . . set STATE_MISSED . . __netif_schedule() . . . set STATE_DEACTIVATED . . qdisc_reset() . . . .<--------------- . synchronize_net() clear __QDISC_STATE_SCHED | . . . | . . . | . some_qdisc_is_busy() . | . return *false* . | . . test STATE_DEACTIVATED | . . __qdisc_run() *not* called | . . . | . . test STATE_MISS | . . __netif_schedule()--------| . . . . . . . . __qdisc_run() is not called by net_tx_atcion() in CPU0 because CPU2 has set STATE_DEACTIVATED flag during dev_deactivate(), and STATE_MISSED is only cleared in __qdisc_run(), __netif_schedule is called at the end of qdisc_run_end(), causing tx action rescheduling problem. qdisc_run() called by net_tx_action() runs in the softirq context, which should has the same semantic as the qdisc_run() called by __dev_xmit_skb() protected by rcu_read_lock_bh(). And there is a synchronize_net() between STATE_DEACTIVATED flag being set and qdisc_reset()/some_qdisc_is_busy in dev_deactivate(), we can safely bail out for the deactived lockless qdisc in net_tx_action(), and qdisc_reset() will reset all skb not dequeued yet. So add the rcu_read_lock() explicitly to protect the qdisc_run() and do the STATE_DEACTIVATED checking in net_tx_action() before calling qdisc_run_begin(). Another option is to do the checking in the qdisc_run_end(), but it will add unnecessary overhead for non-tx_action case, because __dev_queue_xmit() will not see qdisc with STATE_DEACTIVATED after synchronize_net(), the qdisc with STATE_DEACTIVATED can only be seen by net_tx_action() because of __netif_schedule(). The STATE_DEACTIVATED checking in qdisc_run() is to avoid race between net_tx_action() and qdisc_reset(), see: commit d518d2ed8640 ("net/sched: fix race between deactivation and dequeue for NOLOCK qdisc"). As the bailout added above for deactived lockless qdisc in net_tx_action() provides better protection for the race without calling qdisc_run() at all, so remove the STATE_DEACTIVATED checking in qdisc_run(). After qdisc_reset(), there is no skb in qdisc to be dequeued, so clear the STATE_MISSED in dev_reset_queue() too. Fixes: 6b3ba9146fe6 ("net: sched: allow qdiscs to handle locking") Acked-by: Jakub Kicinski <kuba@kernel.org> Signed-off-by: Yunsheng Lin <linyunsheng@huawei.com> V8: Clearing STATE_MISSED before calling __netif_schedule() has avoid the endless rescheduling problem, but there may still be a unnecessary rescheduling, so adjust the commit log. Signed-off-by: David S. Miller <davem@davemloft.net>
Diffstat (limited to 'net')
-rw-r--r--net/core/dev.c26
-rw-r--r--net/sched/sch_generic.c4
2 files changed, 25 insertions, 5 deletions
diff --git a/net/core/dev.c b/net/core/dev.c
index 222b1d322c96..d596cd746353 100644
--- a/net/core/dev.c
+++ b/net/core/dev.c
@@ -5025,25 +5025,43 @@ static __latent_entropy void net_tx_action(struct softirq_action *h)
sd->output_queue_tailp = &sd->output_queue;
local_irq_enable();
+ rcu_read_lock();
+
while (head) {
struct Qdisc *q = head;
spinlock_t *root_lock = NULL;
head = head->next_sched;
- if (!(q->flags & TCQ_F_NOLOCK)) {
- root_lock = qdisc_lock(q);
- spin_lock(root_lock);
- }
/* We need to make sure head->next_sched is read
* before clearing __QDISC_STATE_SCHED
*/
smp_mb__before_atomic();
+
+ if (!(q->flags & TCQ_F_NOLOCK)) {
+ root_lock = qdisc_lock(q);
+ spin_lock(root_lock);
+ } else if (unlikely(test_bit(__QDISC_STATE_DEACTIVATED,
+ &q->state))) {
+ /* There is a synchronize_net() between
+ * STATE_DEACTIVATED flag being set and
+ * qdisc_reset()/some_qdisc_is_busy() in
+ * dev_deactivate(), so we can safely bail out
+ * early here to avoid data race between
+ * qdisc_deactivate() and some_qdisc_is_busy()
+ * for lockless qdisc.
+ */
+ clear_bit(__QDISC_STATE_SCHED, &q->state);
+ continue;
+ }
+
clear_bit(__QDISC_STATE_SCHED, &q->state);
qdisc_run(q);
if (root_lock)
spin_unlock(root_lock);
}
+
+ rcu_read_unlock();
}
xfrm_dev_backlog(sd);
diff --git a/net/sched/sch_generic.c b/net/sched/sch_generic.c
index 795d986e7030..d86c4cca2cab 100644
--- a/net/sched/sch_generic.c
+++ b/net/sched/sch_generic.c
@@ -1177,8 +1177,10 @@ static void dev_reset_queue(struct net_device *dev,
qdisc_reset(qdisc);
spin_unlock_bh(qdisc_lock(qdisc));
- if (nolock)
+ if (nolock) {
+ clear_bit(__QDISC_STATE_MISSED, &qdisc->state);
spin_unlock_bh(&qdisc->seqlock);
+ }
}
static bool some_qdisc_is_busy(struct net_device *dev)