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References: <201503271326.t2RDQxd3056112@svn.freebsd.org>
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Date: Sun, 29 Mar 2015 08:16:46 -0700
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Subject: Re: svn commit: r280759 - head/sys/netinet
From: Adrian Chadd <adrian@freebsd.org>
To: Hans Petter Selasky <hps@selasky.org>
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Cc: "svn-src-head@freebsd.org" <svn-src-head@freebsd.org>,
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 Fabien Thomas <fabient@freebsd.org>
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On 29 March 2015 at 01:13, Hans Petter Selasky <hps@selasky.org> wrote:
> On 03/28/15 20:16, Gleb Smirnoff wrote:
>>
>> +uint16_t
>> +ip_newid(void)
>> +{
>> +
>> +       counter_u64_add(V_ip_id, 1);
>> +       return (htons((*(uint64_t *)zpcpu_get(V_ip_id)) & 0xffff));
>> +}
>
>
> Technically you would need to enter a critical section here, so that the
> current process doesn't get swapped to a different CPU between the counter
> add and the zpcpu_get.

+10000 here.

You can get preempted and shifted to another CPU at almost any point
in time you're not explicitly asking not to be. It's.. frustrating.




-adrian