netdev - Re: [PATCH v2] net-fq: Add WARN

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Message-ID: <99455a63-4a19-e172-a9b4-e7d8935cb1e0@candelatech.com>
Date:   Fri, 8 Jun 2018 07:10:19 -0700
From:   Ben Greear <greearb@...delatech.com>
To:     Cong Wang <xiyou.wangcong@...il.com>
Cc:     Linux Kernel Network Developers <netdev@...r.kernel.org>
Subject: Re: [PATCH v2] net-fq: Add WARN_ON check for null flow.



On 06/07/2018 05:13 PM, Cong Wang wrote:
> On Thu, Jun 7, 2018 at 4:48 PM,  <greearb@...delatech.com> wrote:
>> From: Ben Greear <greearb@...delatech.com>
>>
>> While testing an ath10k firmware that often crashed under load,
>> I was seeing kernel crashes as well.  One of them appeared to
>> be a dereference of a NULL flow object in fq_tin_dequeue.
>>
>> I have since fixed the firmware flaw, but I think it would be
>> worth adding the WARN_ON in case the problem appears again.
>>
>> BUG: unable to handle kernel NULL pointer dereference at 000000000000003c
>> IP: ieee80211_tx_dequeue+0xfb/0xb10 [mac80211]
>
> Instead of adding WARN_ON(), you need to think about
> the locking there, it is suspicious:
>
> fq is from struct ieee80211_local:
>
> struct fq *fq = &local->fq;
>
> tin is from struct txq_info:
>
> struct fq_tin *tin = &txqi->tin;
>
> I don't know if fq and tin are supposed to be 1:1, if not there is
> a bug in the locking, because ->new_flows and ->old_flows are
> both inside tin instead of fq, but they are protected by fq->lock....

Maybe whoever put this code together can take a stab at it.

Thanks,
Ben

-- 
Ben Greear <greearb@...delatech.com>
Candela Technologies Inc  http://www.candelatech.com