netdev - Re: Soft lockup in tc

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Date:   Tue, 20 Dec 2016 23:03:55 -0800
From:   Cong Wang <xiyou.wangcong@...il.com>
To:     Shahar Klein <shahark@...lanox.com>
Cc:     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 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?


Thanks for debugging!