linux-kernel - Re: [PATCH 3/3] sched/nohz: Remove weird error handling from find_new

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <ZR/o8+EJGLMi3uPr@gmail.com>
Date:   Fri, 6 Oct 2023 13:01:07 +0200
From:   Ingo Molnar <mingo@...nel.org>
To:     Peter Zijlstra <peterz@...radead.org>
Cc:     linux-kernel@...r.kernel.org, Juri Lelli <juri.lelli@...hat.com>,
        Vincent Guittot <vincent.guittot@...aro.org>,
        Dietmar Eggemann <dietmar.eggemann@....com>,
        Steven Rostedt <rostedt@...dmis.org>,
        Ben Segall <bsegall@...gle.com>, Mel Gorman <mgorman@...e.de>,
        Daniel Bristot de Oliveira <bristot@...hat.com>,
        Valentin Schneider <vschneid@...hat.com>,
        Frederic Weisbecker <frederic@...nel.org>,
        Joel Fernandes <joel@...lfernandes.org>,
        Thomas Gleixner <tglx@...utronix.de>
Subject: Re: [PATCH 3/3] sched/nohz: Remove weird error handling from
 find_new_ilb()


* Peter Zijlstra <peterz@...radead.org> wrote:

> On Fri, Oct 06, 2023 at 12:25:18PM +0200, Ingo Molnar wrote:
> > find_new_ilb() returns nr_cpu_ids on failure - which is a weird
> > choice in itself: not only is it a global variable, it is
> > a +1 out of bounds CPU index...
> 
> FWIW this is what all the cpumask bitops return when they've exhausted
> the mask. Eg. no bits left set etc..

yeah, which then results in type-forcing uglies like:

   kernel/events/core.c:	if ((unsigned)cpu >= nr_cpu_ids) {
   kernel/events/core.c:   if ((unsigned)cpu >= nr_cpu_ids) {
   kernel/smp.c:	   if ((unsigned)cpu >= nr_cpu_ids || !cpu_online(cpu)) {

:-/

So I don't think this is a particularly well thought-out interface.

Thanks,

	Ingo