From: Yunsheng Lin <linyunsheng@huawei.com>
To: <davem@davemloft.net>, <kuba@kernel.org>
Cc: <olteanv@gmail.com>, <ast@kernel.org>, <daniel@iogearbox.net>,
<andriin@fb.com>, <edumazet@google.com>, <weiwan@google.com>,
<cong.wang@bytedance.com>, <ap420073@gmail.com>,
<netdev@vger.kernel.org>, <linux-kernel@vger.kernel.org>,
<linuxarm@openeuler.org>, <mkl@pengutronix.de>,
<linux-can@vger.kernel.org>, <jhs@mojatatu.com>,
<xiyou.wangcong@gmail.com>, <jiri@resnulli.us>,
<andrii@kernel.org>, <kafai@fb.com>, <songliubraving@fb.com>,
<yhs@fb.com>, <john.fastabend@gmail.com>, <kpsingh@kernel.org>,
<bpf@vger.kernel.org>, <jonas.bonn@netrounds.com>,
<pabeni@redhat.com>, <mzhivich@akamai.com>, <johunt@akamai.com>,
<albcamus@gmail.com>, <kehuan.feng@gmail.com>,
<a.fatoum@pengutronix.de>, <atenart@kernel.org>,
<alexander.duyck@gmail.com>, <hdanton@sina.com>,
<jgross@suse.com>, <JKosina@suse.com>, <mkubecek@suse.cz>,
<bjorn@kernel.org>
Subject: [PATCH net v5 2/3] net: sched: fix endless tx action reschedule during deactivation
Date: Thu, 6 May 2021 09:57:43 +0800 [thread overview]
Message-ID: <1620266264-48109-3-git-send-email-linyunsheng@huawei.com> (raw)
In-Reply-To: <1620266264-48109-1-git-send-email-linyunsheng@huawei.com>
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 endless
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 | . .
. | . .
. | . .
. | . --------->.
. | . | .
test STATE_DEACTIVATED | . | some_qdisc_is_busy()
__qdisc_run() *not* called | . |-----return *true*
. | . .
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 endlessly at the end of qdisc_run_end(), causing endless
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")
Signed-off-by: Yunsheng Lin <linyunsheng@huawei.com>
---
include/net/pkt_sched.h | 7 +------
net/core/dev.c | 26 ++++++++++++++++++++++----
net/sched/sch_generic.c | 4 +++-
3 files changed, 26 insertions(+), 11 deletions(-)
diff --git a/include/net/pkt_sched.h b/include/net/pkt_sched.h
index f5c1bee..6d7b12c 100644
--- a/include/net/pkt_sched.h
+++ b/include/net/pkt_sched.h
@@ -128,12 +128,7 @@ void __qdisc_run(struct Qdisc *q);
static inline void qdisc_run(struct Qdisc *q)
{
if (qdisc_run_begin(q)) {
- /* NOLOCK qdisc must check 'state' under the qdisc seqlock
- * to avoid racing with dev_qdisc_reset()
- */
- if (!(q->flags & TCQ_F_NOLOCK) ||
- likely(!test_bit(__QDISC_STATE_DEACTIVATED, &q->state)))
- __qdisc_run(q);
+ __qdisc_run(q);
qdisc_run_end(q);
}
}
diff --git a/net/core/dev.c b/net/core/dev.c
index 222b1d3..d596cd7 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 9bc73ea..c32ac5b 100644
--- a/net/sched/sch_generic.c
+++ b/net/sched/sch_generic.c
@@ -1170,8 +1170,10 @@ 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)
--
2.7.4
next prev parent reply other threads:[~2021-05-06 1:57 UTC|newest]
Thread overview: 7+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-05-06 1:57 [PATCH net v5 0/3] fix packet stuck problem for lockless qdisc Yunsheng Lin
2021-05-06 1:57 ` [PATCH net v5 1/3] net: sched: " Yunsheng Lin
2021-05-07 23:57 ` Jakub Kicinski
2021-05-08 2:55 ` Yunsheng Lin
2021-05-08 3:05 ` Jakub Kicinski
2021-05-06 1:57 ` Yunsheng Lin [this message]
2021-05-06 1:57 ` [PATCH net v5 3/3] net: sched: fix tx action reschedule issue with stopped queue Yunsheng Lin
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