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From: John Stultz <john.stultz@linaro.org>
To: Liav Rehana <liavr@mellanox.com>
Cc: Thomas Gleixner <tglx@linutronix.de>,
	lkml <linux-kernel@vger.kernel.org>,
	Elad Kanfi <eladkan@mellanox.com>,
	Noam Camus <noamca@mellanox.com>
Subject: Re: [PATCH] timekeeping: Change type of nsec variable to unsigned in its calculation.
Date: Sun, 25 Sep 2016 23:02:04 -0700	[thread overview]
Message-ID: <CALAqxLVAy5mST2ChwQ4hJUXcz8e6wep7y9hYs=fo6ZPtMiGv9Q@mail.gmail.com> (raw)
In-Reply-To: <1474868736-22724-1-git-send-email-liavr@mellanox.com>

On Sun, Sep 25, 2016 at 10:45 PM, Liav Rehana <liavr@mellanox.com> wrote:
> From: Liav Rehana <liavr@mellanox.com>
>
> During the calculation of the nsec variable in the inline function
> timekeeping_delta_to_ns, it may undergo a sign extension if its msb
> is set just before the shift. The sign extension may, in some cases,
> gain it a value near the maximum value of the 64-bit range. This is
> bad when it is later used in a division function, such as
> __iter_div_u64_rem, where the amount of loops it will go through to
> calculate the division will be too large.
> The following commit fixes that chance of sign extension, while
> maintaining the type of the nsec variable as signed for other
> functions that use this variable, for possible legit negative
> time intervals.

Apologies for my foggy memory here (just got off a plane).  But remind
me, is this something that you actually ran into, or is it more of
just a theoretical concern?

If it is something that you did trip on, please describe your case in
the changelog so that the proper urgency is applied when weighing if
such a commit should go into -stable.

thanks
-john

  reply	other threads:[~2016-09-26  6:02 UTC|newest]

Thread overview: 22+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2016-09-26  5:45 [PATCH] timekeeping: Change type of nsec variable to unsigned in its calculation Liav Rehana
2016-09-26  6:02 ` John Stultz [this message]
2016-09-27  0:01 ` Thomas Gleixner
2016-09-27  5:10   ` Liav Rehana
2016-09-27 14:18     ` Thomas Gleixner
2016-09-26  6:13 Liav Rehana
2016-11-19  4:53 John Stultz
2016-11-28 22:50 ` John Stultz
2016-11-29 14:22 ` Thomas Gleixner
2016-11-29 23:57   ` David Gibson
2016-11-30 23:21     ` Thomas Gleixner
2016-12-01  2:12       ` David Gibson
2016-12-01 11:59         ` Thomas Gleixner
2016-12-01 20:23           ` John Stultz
2016-12-01 20:46             ` Thomas Gleixner
2016-12-01 21:19               ` John Stultz
2016-12-01 22:44                 ` Thomas Gleixner
2016-12-01 23:03                   ` John Stultz
2016-12-01 23:08                     ` Thomas Gleixner
2016-12-01 23:32           ` David Gibson
2016-12-02  8:36             ` Thomas Gleixner
2016-12-03  0:33               ` David Gibson

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