Date: Fri, 4 Aug 2017 06:40:41 +0000 From: Colin Percival <cperciva@tarsnap.com> To: Hans Petter Selasky <hps@selasky.org>, cem@freebsd.org Cc: src-committers <src-committers@freebsd.org>, svn-src-all@freebsd.org, svn-src-head@freebsd.org Subject: Re: svn commit: r321985 - head/sys/ofed/drivers/infiniband/core Message-ID: <0100015dabf98040-76cfbcc7-5de4-4e35-9a90-60fa54d31563-000000@email.amazonses.com> In-Reply-To: <bd19c6f8-fa97-c9c5-6318-1778e38dd0a9@selasky.org> References: <201708030918.v739IPVY034866@repo.freebsd.org> <CAG6CVpVL49nVqRs5atub=d2P39EGOqcNtx_Raa8fWtV=BFZXbw@mail.gmail.com> <bd19c6f8-fa97-c9c5-6318-1778e38dd0a9@selasky.org>
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On 08/03/17 23:28, Hans Petter Selasky wrote:
> On 08/03/17 16:37, Conrad Meyer wrote:
>> Is it not important that the subtraction and result are evaluated
>> without truncation?
>
> ticks is a circular counter. Assuming time = 0 and jiffies = -1U, then "delay"
> becomes a very large negative value, because long is used, and the delay <= 0
> check, is no longer working like expected.
>
> Casting to "int" or truncating is the right thing to do in this case.
Signed integer overflow is undefined. Using 'int' is liable to cause problems
after 2^32 ticks.
Colin Percival
>>> Log:
>>> Ticks are 32-bit in FreeBSD.
>>>
>>> MFC after: 3 days
>>> Sponsored by: Mellanox Technologies
>>>
>>> Modified:
>>> head/sys/ofed/drivers/infiniband/core/addr.c
>>>
>>> Modified: head/sys/ofed/drivers/infiniband/core/addr.c
>>> ==============================================================================
>>> --- head/sys/ofed/drivers/infiniband/core/addr.c Thu Aug 3 09:14:43
>>> 2017 (r321984)
>>> +++ head/sys/ofed/drivers/infiniband/core/addr.c Thu Aug 3 09:18:25
>>> 2017 (r321985)
>>> @@ -187,10 +187,10 @@ EXPORT_SYMBOL(rdma_translate_ip);
>>>
>>> static void set_timeout(unsigned long time)
>>> {
>>> - unsigned long delay;
>>> + int delay; /* under FreeBSD ticks are 32-bit */
>>>
>>> delay = time - jiffies;
>>> - if ((long)delay <= 0)
>>> + if (delay <= 0)
>>> delay = 1;
>>>
>>> mod_delayed_work(addr_wq, &work, delay);
--
Colin Percival
Security Officer Emeritus, FreeBSD | The power to serve
Founder, Tarsnap | www.tarsnap.com | Online backups for the truly paranoid
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