linux-kernel - Re: [tip:sched/fifo 44/45] ERROR: modpost: "sched

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Message-ID: <4a0da149-5051-8204-6f34-da4d6e42a78a@arm.com>
Date:   Wed, 29 Jul 2020 12:23:27 +0200
From:   Dietmar Eggemann <dietmar.eggemann@....com>
To:     Qais Yousef <qais.yousef@....com>, peterz@...radead.org
Cc:     Steven Rostedt <rostedt@...dmis.org>,
        kernel test robot <lkp@...el.com>, kbuild-all@...ts.01.org,
        linux-kernel@...r.kernel.org, x86@...nel.org,
        Ingo Molnar <mingo@...nel.org>, sfr@...b.auug.org.au
Subject: Re: [tip:sched/fifo 44/45] ERROR: modpost: "sched_setscheduler"
 undefined!

On 21/07/2020 12:13, Qais Yousef wrote:
> On 07/21/20 10:36, peterz@...radead.org wrote:
>> On Mon, Jul 20, 2020 at 06:19:43PM -0400, Steven Rostedt wrote:
>>> On Mon, 20 Jul 2020 23:49:18 +0200
>>> Peter Zijlstra <peterz@...radead.org> wrote:
>>>
>>>> Steve, would this work for you, or would you prefer renaming the
>>>> parameters as well?
>>>>
>>>
>>> Yeah, that's fine. You don't have any sched_fifo_high() ?
>>
>> Thanks! and no.
>>
>> I'll go write a Changelog and add it to tip/sched/fifo, so that
>> hopefully, sfr can stop complaining about this build fail ;-)
>>
>> I've even argued we should rename fifo_low() to something else, but
>> failed to come up with a sensible name. The intended case is for when
>> you want something above normal but don't particularly care about RT at
>> all.
>>
>> The thing is, once you start adding priorities, even low,med,high, we're
>> back to where we were. And the whole argument is that the kernel cannot
>> set priorities in any sensible fashion.
> 
> Agreed. I am worried about in-kernel users setting random uclamp values too.

Do we really have to restrict in-kernel user?

And avoiding module uclamp abuse is covered by 616d91b68cd5 ("sched:
Remove sched_setscheduler*() EXPORTs").

> This series should do most of the work but there are more pieces needed on-top.
> 
> From what I see we still need to move the sched_setscheduler() from
> include/linux/sched.h to kernel/sched/sched.h. And sched_setattr() too. The
> latter has a single user in kernel/trace/trace_selftest.c to create a deadline
> task. I think that can be easily wrapped with a similar sched_set_dl()
> function and exported instead.

But DL does not have the same issue like the FIFO/RR when it comes to
resource management.
Not sure if we have to restrict in-kernel user.

[...]