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From:   Eric Dumazet <edumazet@google.com>
Date:   Thu, 12 Jul 2018 05:35:56 -0700
Message-ID: <CANn89iLJ+LHK2oMAwWiifg1pa=t2JBi7N6794ixe4aSB_vvuJA@mail.gmail.com>
Subject: Re: [net-next, 1/3] tcp: convert icsk_user_timeout from jiffies to msecs
To:     David Laight <David.Laight@aculab.com>
Cc:     jmaxwell37@gmail.com, David Miller <davem@davemloft.net>,
        Neal Cardwell <ncardwell@google.com>,
        Alexey Kuznetsov <kuznet@ms2.inr.ac.ru>,
        Hideaki YOSHIFUJI <yoshfuji@linux-ipv6.org>,
        netdev <netdev@vger.kernel.org>,
        LKML <linux-kernel@vger.kernel.org>, jmaxwell@redhat.com
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On Thu, Jul 12, 2018 at 1:57 AM David Laight <David.Laight@aculab.com> wrote:
>
> From: Jon Maxwell Sent: 12 July 2018 01:36
> ...
> > - (s32)(tcp_time_stamp(tp) - start_ts) >
> > - jiffies_to_msecs(icsk->icsk_user_timeout))
> > + (s32)(tcp_time_stamp(tp) - start_ts) > icsk->icsk_user_timeout)
>
> That has never been tested properly.
> icsk_user_timeout is u32 so the comparison is unsigned and the (s32) cast
> has no effect.
>

The existing code had this ' bug' already.

Please do not blame this patch, and send a patch if you believe there
is an issue ?

In my opinion, the (s32) here is a reminder for the reader of the
width of the expression,
more than anything, since there is no chance the result can be negative.