netdev - Re: Soft lockup in tc

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Date:   Wed, 21 Dec 2016 13:25:18 +0200
From:   Shahar Klein <shahark@...lanox.com>
To:     Cong Wang <xiyou.wangcong@...il.com>
CC:     <shahark@...lanox.com>, Daniel Borkmann <daniel@...earbox.net>,
        Or Gerlitz <gerlitz.or@...il.com>,
        Linux Netdev List <netdev@...r.kernel.org>,
        Roi Dayan <roid@...lanox.com>,
        David Miller <davem@...emloft.net>,
        Jiri Pirko <jiri@...lanox.com>,
        John Fastabend <john.fastabend@...il.com>,
        Hadar Hen Zion <hadarh@...lanox.com>
Subject: Re: Soft lockup in tc_classify



On 12/21/2016 9:03 AM, Cong Wang wrote:
> On Tue, Dec 20, 2016 at 10:44 PM, Shahar Klein <shahark@...lanox.com> wrote:
>>
>> Tried it with same results
>
> This piece is pretty interesting:
>
> [  408.554689] DEBUGG:SK thread-2853[cpu-1] setting tp_created to 1
> tp=ffff94b5b02805a0 back=ffff94b9ea932060
> [  408.574258] DEBUGG:SK thread-2853[cpu-1] add/change filter by:
> fl_get [cls_flower] tp=ffff94b5b02805a0 tp->next=ffff94b9ea932060
> [  408.587849] DEBUGG:SK destroy ffff94b5b0280780 tcf_destroy:1905
> [  408.595862] DEBUGG:SK thread-2845[cpu-1] add/change filter by:
> fl_get [cls_flower] tp=ffff94b5b02805a0 tp->next=ffff94b5b02805a0
>
> Looks like you added a debug printk inside tcf_destroy() too,
> which seems racy with filter creation, it should not happen since
> in both cases we take RTNL lock.
>
> Don't know if changing all RCU_INIT_POINTER in that file to
> rcu_assign_pointer could help anything or not. Mind to try?
>

Tried it with same results

>
> Thanks for debugging!
>

View attachment "cls_api_no_RCU.c.diff" of type "text/plain" (2704 bytes)