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@xxxxxxxxxx>
> ---
>  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@xxxxxxxxxx>