linux-kernel - Re: [PATCH] ntp: fix bug in adjtimex reading time offset

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Message-ID: <87iks7y6f4.ffs@tglx>
Date: Thu, 28 Nov 2024 11:54:55 +0100
From: Thomas Gleixner <tglx@...utronix.de>
To: Richard Cochran <richardcochran@...il.com>
Cc: "Dalmas, Marcelo (GE Vernova)" <marcelo.dalmas@...com>,
 "jstultz@...gle.com" <jstultz@...gle.com>, "sboyd@...nel.org"
 <sboyd@...nel.org>, "linux-kernel@...r.kernel.org"
 <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] ntp: fix bug in adjtimex reading time offset

On Wed, Nov 27 2024 at 18:39, Thomas Gleixner wrote:
> On Wed, Nov 27 2024 at 18:35, Thomas Gleixner wrote:
>> On Wed, Nov 27 2024 at 08:05, Richard Cochran wrote:
>>> On Wed, Nov 27, 2024 at 03:10:30PM +0100, Thomas Gleixner wrote:
>>>     The patch was generated by the following coccinelle script:
>>>
>>>     ...
>>>
>>> So I guess combining random other manual fixes into a patch that
>>> claims to be generated is a bad idea?
>>
>> Indeed. I just figured out why the cast is there. txc::time_offset is of
>> type 'long long', so the division triggers a build fail on 32-bit.
>>
>> It want's to be:
>>
>>    txc->time_offset = div_s64(txc->time_offset, NSEC_PER_USEC);
>
> Or simpler by using a (s32) cast instead, which is sufficient as
> time_offset must be in the range of [INT_MIN ... INT_MAX] because
> NTP_SCALE_SHIFT is 32.

But that requires a comment while div_s64() is self explaining and it
does not matter performance wise as the 32bit implementations reduce it
to a 32bit/32bit division.

Thanks,

        tglx