linux-kernel - Re: [PATCH] kfence: use TASK_IDLE when awaiting allocation

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: <YKeBvR0sZGTqX4fG@elver.google.com>
Date:   Fri, 21 May 2021 11:47:41 +0200
From:   Marco Elver <elver@...gle.com>
To:     David Laight <David.Laight@...lab.com>
Cc:     "akpm@...ux-foundation.org" <akpm@...ux-foundation.org>,
        "glider@...gle.com" <glider@...gle.com>,
        "dvyukov@...gle.com" <dvyukov@...gle.com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "linux-mm@...ck.org" <linux-mm@...ck.org>,
        "kasan-dev@...glegroups.com" <kasan-dev@...glegroups.com>,
        Mel Gorman <mgorman@...e.de>,
        "stable@...r.kernel.org" <stable@...r.kernel.org>
Subject: Re: [PATCH] kfence: use TASK_IDLE when awaiting allocation

On Fri, May 21, 2021 at 09:39AM +0000, David Laight wrote:
> From: Marco Elver
> > Sent: 21 May 2021 09:32
> > 
> > Since wait_event() uses TASK_UNINTERRUPTIBLE by default, waiting for an
> > allocation counts towards load. However, for KFENCE, this does not make
> > any sense, since there is no busy work we're awaiting.
> > 
> > Instead, use TASK_IDLE via wait_event_idle() to not count towards load.
> 
> Doesn't that let the process be interruptible by a signal.
> Which is probably not desirable.
> 
> There really ought to be a way of sleeping with TASK_UNINTERRUPTIBLE
> without changing the load-average.

That's what TASK_IDLE is:

	include/linux/sched.h:#define TASK_IDLE                 (TASK_UNINTERRUPTIBLE | TASK_NOLOAD)

See https://lore.kernel.org/lkml/alpine.LFD.2.11.1505112154420.1749@ja.home.ssi.bg/T/

Thanks,
-- Marco

> IIRC the load-average is really intended to include processes
> that are waiting for disk - especially for swap.
> 
> 	David
> 
> -
> Registered Address Lakeside, Bramley Road, Mount Farm, Milton Keynes, MK1 1PT, UK
> Registration No: 1397386 (Wales)