linux-kernel - Re: [PATCH] sched/fair: Use 'unsigned long' for group_shares,group

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Message-ID: <20190415124617.GP11158@hirez.programming.kicks-ass.net>
Date:   Mon, 15 Apr 2019 14:46:17 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     Cheng Jian <cj.chengjian@...wei.com>
Cc:     huawei.libin@...wei.com, xiexiuqi@...wei.com,
        yangyingliang@...wei.com, mingo@...hat.com,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] sched/fair: Use 'unsigned long' for
 group_shares,group_runnable

On Sat, Apr 13, 2019 at 03:32:34AM +0000, Cheng Jian wrote:
> group_share and group_runnable are tracked as 'unsigned long',
> however some functions using them as 'long' which is ultimately
> assigned back to 'unsigned long' variables in reweight_entity.
> 
> Since there is not scope on using a different and signed type,
> this change improves code consistency and avoids further type
> conversions. More important, to prevent undefined behavior
> caused by overflow.

There is no undefined behaviour due to overflow. UBSAN is broken,
upgrade to GCC8 or later.