lkml.org 
[lkml]   [2020]   [Sep]   [2]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
Patch in this message
/
SubjectRe: [PATCH net-next] net: sch_generic: aviod concurrent reset and enqueue op for lockless qdisc
From
Date


On 9/2/20 1:14 AM, Yunsheng Lin wrote:
> On 2020/9/2 15:32, Eric Dumazet wrote:
>>
>>
>> On 9/1/20 11:34 PM, Yunsheng Lin wrote:
>>
>>>
>>> I am not familiar with TCQ_F_CAN_BYPASS.
>>> From my understanding, the problem is that there is no order between
>>> qdisc enqueuing and qdisc reset.
>>
>> Thw qdisc_reset() should be done after rcu grace period, when there is guarantee no enqueue is in progress.
>>
>> qdisc_destroy() already has a qdisc_reset() call, I am not sure why qdisc_deactivate() is also calling qdisc_reset()
>
> That is a good point.
> Do we allow skb left in qdisc when the qdisc is deactivated state?
> And qdisc_destroy() is not always called after qdisc_deactivate() is called.
> If we allow skb left in qdisc when the qdisc is deactivated state, then it is
> huge change of semantics for qdisc_deactivate(), and I am not sure how many
> cases will affected by this change.

All I am saying is that the qdisc_reset() in qdisc_deactivate() seems
at the wrong place.

This certainly can be deferred _after_ the rcu grace period we already have in dev_deactivate_many()

Something like this nicer patch.

net/sched/sch_generic.c | 22 ++++------------------
1 file changed, 4 insertions(+), 18 deletions(-)


diff --git a/net/sched/sch_generic.c b/net/sched/sch_generic.c
index 265a61d011dfaa7ec0f8fb8aaede920784f690c9..0eaa99e4f8de643724c0942ee1a2e9516eed65c0 100644
--- a/net/sched/sch_generic.c
+++ b/net/sched/sch_generic.c
@@ -1131,24 +1131,10 @@ EXPORT_SYMBOL(dev_activate);

static void qdisc_deactivate(struct Qdisc *qdisc)
{
- bool nolock = qdisc->flags & TCQ_F_NOLOCK;
-
if (qdisc->flags & TCQ_F_BUILTIN)
return;
- if (test_bit(__QDISC_STATE_DEACTIVATED, &qdisc->state))
- return;
-
- if (nolock)
- spin_lock_bh(&qdisc->seqlock);
- spin_lock_bh(qdisc_lock(qdisc));

set_bit(__QDISC_STATE_DEACTIVATED, &qdisc->state);
-
- qdisc_reset(qdisc);
-
- spin_unlock_bh(qdisc_lock(qdisc));
- if (nolock)
- spin_unlock_bh(&qdisc->seqlock);
}

static void dev_deactivate_queue(struct net_device *dev,
@@ -1184,6 +1170,9 @@ static bool some_qdisc_is_busy(struct net_device *dev)
val = (qdisc_is_running(q) ||
test_bit(__QDISC_STATE_SCHED, &q->state));

+ if (!val)
+ qdisc_reset(q);
+
spin_unlock_bh(root_lock);

if (val)
@@ -1213,10 +1202,7 @@ void dev_deactivate_many(struct list_head *head)
dev_watchdog_down(dev);
}

- /* Wait for outstanding qdisc-less dev_queue_xmit calls.
- * This is avoided if all devices are in dismantle phase :
- * Caller will call synchronize_net() for us
- */
+ /* Wait for outstanding dev_queue_xmit calls. */
synchronize_net();

/* Wait for outstanding qdisc_run calls. */

\
 
 \ /
  Last update: 2020-09-02 11:21    [W:0.465 / U:0.168 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site