netdev - Re: [PATCH] net: optimize cmpxchg in ip_idents

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Message-ID: <20200117180324.GA2623847@rani.riverdale.lan>
Date:   Fri, 17 Jan 2020 13:03:26 -0500
From:   Arvind Sankar <nivedita@...m.mit.edu>
To:     Eric Dumazet <eric.dumazet@...il.com>
Cc:     Peter Zijlstra <peterz@...radead.org>,
        Shaokun Zhang <zhangshaokun@...ilicon.com>,
        David Miller <davem@...emloft.net>, netdev@...r.kernel.org,
        linux-kernel@...r.kernel.org, jinyuqi@...wei.com,
        kuznet@....inr.ac.ru, yoshfuji@...ux-ipv6.org, edumazet@...gle.com,
        guoyang2@...wei.com, Will Deacon <will@...nel.org>
Subject: Re: [PATCH] net: optimize cmpxchg in ip_idents_reserve

On Fri, Jan 17, 2020 at 08:35:07AM -0800, Eric Dumazet wrote:
> 
> 
> On 1/17/20 4:32 AM, Peter Zijlstra wrote:
> 
> > 
> > That's crazy, just accept that UBSAN is taking bonghits and ignore it.
> > Use atomic_add_return() unconditionally.
> > 
> 
> Yes, we might simply add a comment so that people do not bug us if
> their compiler is too old.
> 
> /* If UBSAN reports an error there, please make sure your compiler
>  * supports -fno-strict-overflow before reporting it.
>  */
> return atomic_add_return(segs + delta, p_id) - segs;
> 

Do we need that comment any more? The flag was apparently introduced in
gcc-4.2 and we only support 4.6+ anyway?