linux-kernel - Re: [PATCH] net: optimize cmpxchg in ip_idents

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Message-ID: <CANn89iJ02iFxGibdqO+YWVYX4q4J=W9vv7HOpMVqNK-qZvHcQw@mail.gmail.com>
Date:   Sat, 18 Jan 2020 20:12:48 -0800
From:   Eric Dumazet <edumazet@...gle.com>
To:     Shaokun Zhang <zhangshaokun@...ilicon.com>
Cc:     Peter Zijlstra <peterz@...radead.org>,
        Eric Dumazet <eric.dumazet@...il.com>,
        David Miller <davem@...emloft.net>,
        netdev <netdev@...r.kernel.org>,
        LKML <linux-kernel@...r.kernel.org>, jinyuqi@...wei.com,
        Alexey Kuznetsov <kuznet@....inr.ac.ru>,
        Hideaki YOSHIFUJI <yoshfuji@...ux-ipv6.org>,
        guoyang2@...wei.com, Will Deacon <will@...nel.org>
Subject: Re: [PATCH] net: optimize cmpxchg in ip_idents_reserve

On Sat, Jan 18, 2020 at 7:47 PM Shaokun Zhang
<zhangshaokun@...ilicon.com> wrote:
>

> We have used the atomic_add_return[1], but it makes the UBSAN unhappy followed
> by the comment.
> It seems that Eric also agreed to do it if some comments are added. I will do
> it later.
>
> Thanks,
> Shaokun
>
> [1] https://lkml.org/lkml/2019/7/26/217
>

In case you have missed it, we needed a proper analysis.
My feedback was quite simple :

<quote>
Have you first checked that current UBSAN versions will not complain anymore ?
</quote>

You never did this work, never replied to my question, and months
later you come back
with a convoluted patch while we simply can proceed with a revert now
we are sure that linux kernels are compiled with the proper option.

As mentioned yesterday, no need for a comment.
Instead the changelog should be explaining why the revert is now safe.