netdev - Re: [PATCH net] net: systemport: Fix 64-bit stats deadlock

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Message-ID: <C414D433-28B3-4BA4-938B-B5C868918532@gmail.com>
Date:   Fri, 15 Sep 2017 14:28:40 -0700
From:   Florian Fainelli <f.fainelli@...il.com>
To:     David Miller <davem@...emloft.net>
CC:     netdev@...r.kernel.org, edumazet@...gle.com, jqiaoulk@...il.com
Subject: Re: [PATCH net] net: systemport: Fix 64-bit stats deadlock

On September 15, 2017 2:25:11 PM PDT, David Miller <davem@...emloft.net> wrote:
>From: Florian Fainelli <f.fainelli@...il.com>
>Date: Tue, 12 Sep 2017 13:14:26 -0700
>
>> We can enter a deadlock situation because there is no sufficient
>protection
>> when ndo_get_stats64() runs in process context to guard against RX or
>TX NAPI
>> contexts running in softirq, this can lead to the following lockdep
>splat and
>> actual deadlock was experienced as well with an iperf session in the
>background
>> and a while loop doing ifconfig + ethtool.
> ...
>> So just remove the u64_stats_update_begin()/end() pair in
>ndo_get_stats64()
>> since it does not appear to be useful for anything. No inconsistency
>was
>> observed with either ifconfig or ethtool, global TX counts equal the
>sum of
>> per-queue TX counts on a 32-bit architecture.
>> 
>> Fixes: 10377ba7673d ("net: systemport: Support 64bit statistics")
>> Signed-off-by: Florian Fainelli <f.fainelli@...il.com>
>
>Applied.

FYI, there is another patch needed to ensure consistency between ethtool reported stats and netdevice stats, will submit that after some more testing. Thanks!

-- 
Florian