netdev - Re: [PATCH net] net: prevent load/store tearing on sk->sk

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Message-ID: <CANn89i+dqWytEiB+CTsF2drNN3Jg7DY7rbhjTDiiVDWizY3jCQ@mail.gmail.com>
Date:   Tue, 5 Nov 2019 08:50:55 -0800
From:   Eric Dumazet <edumazet@...gle.com>
To:     Deepa Dinamani <deepa.kernel@...il.com>
Cc:     "David S . Miller" <davem@...emloft.net>,
        netdev <netdev@...r.kernel.org>,
        Eric Dumazet <eric.dumazet@...il.com>,
        Arnd Bergmann <arnd@...db.de>
Subject: Re: [PATCH net] net: prevent load/store tearing on sk->sk_stamp

On Tue, Nov 5, 2019 at 8:25 AM Deepa Dinamani <deepa.kernel@...il.com> wrote:

> I do not see any harm with this. Does it cause performance degradation?
>

It does not change compiler output, at least for common GCC versions.

It would change things if a hypothetical caller would do for example :

ktime_t res;

res = sock_read_timestamp(sk);
res = sock_read_timestamp(sk);

Since without  the READ_ONCE(), compiler could remove the first instance.

> Acked-by: Deepa Dinamani <deepa.kernel@...il.com>
>
> -Deepa