linux-kernel - Re: [PATCH 0/3] drm: commit

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Message-ID: <20200924161356.5kezxwiqwtbi3o2p@e107158-lin.cambridge.arm.com>
Date:   Thu, 24 Sep 2020 17:15:00 +0100
From:   Qais Yousef <qais.yousef@....com>
To:     Rob Clark <robdclark@...il.com>,
        dri-devel <dri-devel@...ts.freedesktop.org>,
        Rob Clark <robdclark@...omium.org>,
        Peter Zijlstra <peterz@...radead.org>,
        linux-arm-msm <linux-arm-msm@...r.kernel.org>,
        open list <linux-kernel@...r.kernel.org>,
        Tim Murray <timmurray@...gle.com>, Tejun Heo <tj@...nel.org>
Subject: Re: [PATCH 0/3] drm: commit_work scheduling

On 09/24/20 10:49, Daniel Vetter wrote:

[...]

> > > I also thought kernel threads can be distinguished from others, so
> > > userspace shouldn't be able to sneak in and get elevated by accident.
> > 
> > I guess maybe you could look at the parent?  I still would like to
> > think that we could come up with something a bit less shaking than
> > matching thread names by regexp..
> 
> ps marks up kernel threads with [], so there is a way. But I haven't
> looked at what it is exactly that tells kernel threads apart from others.
> 
> But aside from that sounds like "match right kernel thread with regex and
> set its scheduler class" is how this is currently done, if I'm
> understanding what Tejun and Peter said correctly.
> 
> Not pretty, but also *shrug* ...

Isn't there a real danger that a sneaky application names its threads to match
this regex and get a free promotion to RT without having the capability to do
so?

Cheers

--
Qais Yousef