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authorYunsheng Lin <linyunsheng@huawei.com>2021-05-14 06:17:00 +0300
committerDavid S. Miller <davem@davemloft.net>2021-05-15 01:05:46 +0300
commit102b55ee92f9fda4dde7a45d2b20538e6e3e3d1e (patch)
treeb99ff14fdb63b9a505bab2d45f01289a925424a5 /include/net/pkt_sched.h
parenta90c57f2cedd52a511f739fb55e6244e22e1a2fb (diff)
downloadlinux-102b55ee92f9fda4dde7a45d2b20538e6e3e3d1e.tar.xz
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 'include/net/pkt_sched.h')
-rw-r--r--include/net/pkt_sched.h7
1 files changed, 1 insertions, 6 deletions
diff --git a/include/net/pkt_sched.h b/include/net/pkt_sched.h
index f5c1bee0cd6a..6d7b12cba015 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);
}
}