[PATCH stable] net: sch_generic: fix the missing new qdisc assignment bug

[PATCH stable] net: sch_generic: fix the missing new qdisc assignment bug

[Yunsheng Lin]

commit 2fb541c862c9 ("net: sch_generic: aviod concurrent reset and enqueue op for lockless qdisc")

When the above upstream commit is backported to stable kernel,
one assignment is missing, which causes two problems reported
by Joakim and Vishwanath, see [1] and [2].

So add the assignment back to fix it.

1. https://www.spinics.net/lists/netdev/msg693916.html
2. https://www.spinics.net/lists/netdev/msg695131.html

Fixes: 749cc0b0c7f3 ("net: sch_generic: aviod concurrent reset and enqueue op for lockless qdisc")
Signed-off-by: Yunsheng Lin <linyunsheng@huawei.com>
---
 net/sched/sch_generic.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/net/sched/sch_generic.c b/net/sched/sch_generic.c
index 0e275e1..6e6147a 100644
--- a/net/sched/sch_generic.c
+++ b/net/sched/sch_generic.c
@@ -1127,10 +1127,13 @@ static void dev_deactivate_queue(struct net_device *dev,
 				 void *_qdisc_default)
 {
 	struct Qdisc *qdisc = rtnl_dereference(dev_queue->qdisc);
+	struct Qdisc *qdisc_default = _qdisc_default;
 
 	if (qdisc) {
 		if (!(qdisc->flags & TCQ_F_BUILTIN))
 			set_bit(__QDISC_STATE_DEACTIVATED, &qdisc->state);
+
+		rcu_assign_pointer(dev_queue->qdisc, qdisc_default);
 	}
 }
 
-- 
2.7.4

Re: [PATCH stable] net: sch_generic: fix the missing new qdisc assignment bug

[Vishwanath Pai]

On 11/2/20 10:25 PM, Yunsheng Lin wrote:
 > commit 2fb541c862c9 ("net: sch_generic: aviod concurrent reset and 
enqueue op for lockless qdisc")
 >
 > When the above upstream commit is backported to stable kernel,
 > one assignment is missing, which causes two problems reported
 > by Joakim and Vishwanath, see [1] and [2].
 >
 > So add the assignment back to fix it.
 >
 > 1. 
https://urldefense.com/v3/__https://www.spinics.net/lists/netdev/msg693916.html__;!!GjvTz_vk!AqzcoNtwXeDu-vDNRKnOiOWYmi4B-2atZZExjZTvpp2jeJ9asOyQBVUtQyBp$
 > 2. 
https://urldefense.com/v3/__https://www.spinics.net/lists/netdev/msg695131.html__;!!GjvTz_vk!AqzcoNtwXeDu-vDNRKnOiOWYmi4B-2atZZExjZTvpp2jeJ9asOyQBQlaitCQ$
 >
 > Fixes: 749cc0b0c7f3 ("net: sch_generic: aviod concurrent reset and 
enqueue op for lockless qdisc")
 > Signed-off-by: Yunsheng Lin <linyunsheng@huawei.com>
 > ---
 >  net/sched/sch_generic.c | 3 +++
 >  1 file changed, 3 insertions(+)
 >
 > diff --git a/net/sched/sch_generic.c b/net/sched/sch_generic.c
 > index 0e275e1..6e6147a 100644
 > --- a/net/sched/sch_generic.c
 > +++ b/net/sched/sch_generic.c
 > @@ -1127,10 +1127,13 @@ static void dev_deactivate_queue(struct 
net_device *dev,
 >                   void *_qdisc_default)
 >  {
 >      struct Qdisc *qdisc = rtnl_dereference(dev_queue->qdisc);
 > +    struct Qdisc *qdisc_default = _qdisc_default;
 >
 >      if (qdisc) {
 >          if (!(qdisc->flags & TCQ_F_BUILTIN))
 >              set_bit(__QDISC_STATE_DEACTIVATED, &qdisc->state);
 > +
 > +        rcu_assign_pointer(dev_queue->qdisc, qdisc_default);
 >      }
 >  }
 >

I have tested the patch on v5.4.71 and it fixes our issues.

Tested-by: Vishwanath Pai <vpai@akamai.com>

Re: [PATCH stable] net: sch_generic: fix the missing new qdisc assignment bug

[Jakub Kicinski]

On Tue, 3 Nov 2020 11:25:38 +0800 Yunsheng Lin wrote:
> commit 2fb541c862c9 ("net: sch_generic: aviod concurrent reset and enqueue op for lockless qdisc")
> 
> When the above upstream commit is backported to stable kernel,
> one assignment is missing, which causes two problems reported
> by Joakim and Vishwanath, see [1] and [2].
> 
> So add the assignment back to fix it.
> 
> 1. https://www.spinics.net/lists/netdev/msg693916.html
> 2. https://www.spinics.net/lists/netdev/msg695131.html
> 
> Fixes: 749cc0b0c7f3 ("net: sch_generic: aviod concurrent reset and enqueue op for lockless qdisc")
> Signed-off-by: Yunsheng Lin <linyunsheng@huawei.com>

Acked-by: Jakub Kicinski <kuba@kernel.org>

Re: [PATCH stable] net: sch_generic: fix the missing new qdisc assignment bug

[Greg KH]

On Tue, Nov 03, 2020 at 11:25:38AM +0800, Yunsheng Lin wrote:
> commit 2fb541c862c9 ("net: sch_generic: aviod concurrent reset and enqueue op for lockless qdisc")
> 
> When the above upstream commit is backported to stable kernel,
> one assignment is missing, which causes two problems reported
> by Joakim and Vishwanath, see [1] and [2].
> 
> So add the assignment back to fix it.
> 
> 1. https://www.spinics.net/lists/netdev/msg693916.html
> 2. https://www.spinics.net/lists/netdev/msg695131.html
> 
> Fixes: 749cc0b0c7f3 ("net: sch_generic: aviod concurrent reset and enqueue op for lockless qdisc")
> Signed-off-by: Yunsheng Lin <linyunsheng@huawei.com>
> ---
>  net/sched/sch_generic.c | 3 +++
>  1 file changed, 3 insertions(+)

What kernel tree(s) does this need to be backported to?

thanks,

greg k-h

Re: [PATCH stable] net: sch_generic: fix the missing new qdisc assignment bug

[Yunsheng Lin]

On 2020/11/9 20:46, Greg KH wrote:
> On Tue, Nov 03, 2020 at 11:25:38AM +0800, Yunsheng Lin wrote:
>> commit 2fb541c862c9 ("net: sch_generic: aviod concurrent reset and enqueue op for lockless qdisc")
>>
>> When the above upstream commit is backported to stable kernel,
>> one assignment is missing, which causes two problems reported
>> by Joakim and Vishwanath, see [1] and [2].
>>
>> So add the assignment back to fix it.
>>
>> 1. https://www.spinics.net/lists/netdev/msg693916.html
>> 2. https://www.spinics.net/lists/netdev/msg695131.html
>>
>> Fixes: 749cc0b0c7f3 ("net: sch_generic: aviod concurrent reset and enqueue op for lockless qdisc")
>> Signed-off-by: Yunsheng Lin <linyunsheng@huawei.com>
>> ---
>>  net/sched/sch_generic.c | 3 +++
>>  1 file changed, 3 insertions(+)
> 
> What kernel tree(s) does this need to be backported to?

4.19.x and 5.4.x

Thanks

> 
> thanks,
> 
> greg k-h
> .
> 

Re: [PATCH stable] net: sch_generic: fix the missing new qdisc assignment bug

[Greg KH]

On Tue, Nov 10, 2020 at 08:58:17AM +0800, Yunsheng Lin wrote:
> On 2020/11/9 20:46, Greg KH wrote:
> > On Tue, Nov 03, 2020 at 11:25:38AM +0800, Yunsheng Lin wrote:
> >> commit 2fb541c862c9 ("net: sch_generic: aviod concurrent reset and enqueue op for lockless qdisc")
> >>
> >> When the above upstream commit is backported to stable kernel,
> >> one assignment is missing, which causes two problems reported
> >> by Joakim and Vishwanath, see [1] and [2].
> >>
> >> So add the assignment back to fix it.
> >>
> >> 1. https://www.spinics.net/lists/netdev/msg693916.html
> >> 2. https://www.spinics.net/lists/netdev/msg695131.html
> >>
> >> Fixes: 749cc0b0c7f3 ("net: sch_generic: aviod concurrent reset and enqueue op for lockless qdisc")
> >> Signed-off-by: Yunsheng Lin <linyunsheng@huawei.com>
> >> ---
> >>  net/sched/sch_generic.c | 3 +++
> >>  1 file changed, 3 insertions(+)
> > 
> > What kernel tree(s) does this need to be backported to?
> 
> 4.19.x and 5.4.x

Now queued up, thanks.

greg k-h

Re: [PATCH stable] net: sch_generic: fix the missing new qdisc assignment bug

[Brian Norris]

On Tue, Nov 03, 2020 at 11:25:38AM +0800, Yunsheng Lin wrote:
> commit 2fb541c862c9 ("net: sch_generic: aviod concurrent reset and enqueue op for lockless qdisc")
> 
> When the above upstream commit is backported to stable kernel,
> one assignment is missing, which causes two problems reported
> by Joakim and Vishwanath, see [1] and [2].
> 
> So add the assignment back to fix it.
> 
> 1. https://www.spinics.net/lists/netdev/msg693916.html
> 2. https://www.spinics.net/lists/netdev/msg695131.html
> 
> Fixes: 749cc0b0c7f3 ("net: sch_generic: aviod concurrent reset and enqueue op for lockless qdisc")
> Signed-off-by: Yunsheng Lin <linyunsheng@huawei.com>

For whatever it's worth, we've seen similar problems (particularly,
ENOBUFS on AF_PACKET sockets) and have tested this fix on 4.19.y (we're
also queueing it up on our 5.4.y branch, but haven't tested it as much):

Tested-by: Brian Norris <briannorris@chromium.org>

Thanks!