linux-kernel - Re: [PATCH 2/2] sched: Don't report SCHED_FLAG_SUGOV in sched

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Date:   Wed, 28 Jul 2021 10:39:38 +0100
From:   Quentin Perret <qperret@...gle.com>
To:     Juri Lelli <juri.lelli@...hat.com>
Cc:     Ingo Molnar <mingo@...hat.com>,
        Peter Zijlstra <peterz@...radead.org>,
        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>,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH 2/2] sched: Don't report SCHED_FLAG_SUGOV in
 sched_getattr()

On Wednesday 28 Jul 2021 at 11:12:03 (+0200), Juri Lelli wrote:
> Hi Quentin,
> 
> On 27/07/21 11:11, Quentin Perret wrote:
> > SCHED_FLAG_SUGOV is supposed to be a kernel-only flag that userspace
> > cannot interact with. However, sched_getattr() currently reports it
> > in sched_flags if called on a sugov worker even though it is not
> > actually defined in a UAPI header. To avoid this, make sure to
> > clean-up the sched_flags field in sched_getattr() before returning to
> > userspace.
> > 
> > Signed-off-by: Quentin Perret <qperret@...gle.com>
> > ---
> >  kernel/sched/core.c | 1 +
> >  1 file changed, 1 insertion(+)
> > 
> > diff --git a/kernel/sched/core.c b/kernel/sched/core.c
> > index 2d9ff40f4661..d8f489dcc383 100644
> > --- a/kernel/sched/core.c
> > +++ b/kernel/sched/core.c
> > @@ -7535,6 +7535,7 @@ SYSCALL_DEFINE4(sched_getattr, pid_t, pid, struct sched_attr __user *, uattr,
> >  		kattr.sched_priority = p->rt_priority;
> >  	else
> >  		kattr.sched_nice = task_nice(p);
> > +	kattr.sched_flags &= SCHED_FLAG_ALL;
> 
> Maybe we can do this in the previous patch so that it's kept confined to
> deadline bits?

That works too, it just felt like this could happen again if we start
using non-standard flags outside of deadline for any reason at some
point in the future. But no strong opinion really.

Cheers,
Quentin