linux-kernel - Re: [PATCH v3] skbuff: fix a data race in skb_queue

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Message-ID: <495f79f5-ae27-478a-2a1d-6d3fba2d4334@gmail.com>
Date:   Thu, 6 Feb 2020 10:22:02 -0800
From:   Eric Dumazet <eric.dumazet@...il.com>
To:     "Jason A. Donenfeld" <Jason@...c4.com>,
        Eric Dumazet <eric.dumazet@...il.com>
Cc:     cai@....pw, Netdev <netdev@...r.kernel.org>,
        LKML <linux-kernel@...r.kernel.org>,
        Marco Elver <elver@...gle.com>,
        Dmitry Vyukov <dvyukov@...gle.com>
Subject: Re: [PATCH v3] skbuff: fix a data race in skb_queue_len()



On 2/6/20 10:12 AM, Jason A. Donenfeld wrote:
> On Thu, Feb 6, 2020 at 6:10 PM Eric Dumazet <eric.dumazet@...il.com> wrote:
>> Unfortunately we do not have ADD_ONCE() or something like that.
> 
> I guess normally this is called "atomic_add", unless you're thinking
> instead about something like this, which generates the same
> inefficient code as WRITE_ONCE:
> 
> #define ADD_ONCE(d, s) *(volatile typeof(d) *)&(d) += (s)
> 

Dmitry Vyukov had a nice suggestion few months back how to implement this.

https://lkml.org/lkml/2019/10/5/6