linux-kernel - Re: [PATCH RFC 5/5] kdbus: improve tests on incrementing quota

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Message-ID: <CANq1E4ShamZHhCNdwAL2oYEcij-YZifEwcqN_AviV7R7TKLdtQ@mail.gmail.com>
Date:	Sat, 4 Jul 2015 13:48:06 +0200
From:	David Herrmann <dh.herrmann@...il.com>
To:	Sergei Zviagintsev <sergei@...v.net>
Cc:	Djalal Harouni <tixxdz@...ndz.org>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	Daniel Mack <daniel@...que.org>,
	David Herrmann <dh.herrmann@...glemail.com>,
	linux-kernel <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH RFC 5/5] kdbus: improve tests on incrementing quota

Hi

On Thu, Jul 2, 2015 at 7:47 PM, Sergei Zviagintsev <sergei@...v.net> wrote:
> Hi Djalal,
>
> On Thu, Jul 02, 2015 at 03:13:41PM +0100, Djalal Harouni wrote:
> [...]
>> > My journey with this piece of code began from spotting and immediately
>> > "fixing" the overflow issue :) Then I decided to dig into the
>> > out-of-tree repo to find the origin of this line. What I found were
>> > commits af8e2f750985 and ac5c385cc67a in which Djalal "fixed" it as
>> > well, but then reverted back to the original code.
>> >
>> > Surely we can drop this explanation, but if one of kdbus maintainers
>> > experienced difficulties in understanding this piece of code, wouldn't
>> > one who sees this code in the first time have the same issues?
>> Yes there was lot of work in this area to make sure that the quota
>> accounting is correct! the previous commits the one that tried to clean
>> things up and the revert were both correct :-) ,
>
> I cannot agree that commit af8e2f750985 in out-of-tree repo was correct.

Exactly, that's why the commit got reverted. The U32_MAX check is
*not* about overflows of pool-memory, but rather about overflows in
quota-accounting.

Thanks
David
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