linux-kernel - Re: [GIT pull] sched/urgent for v5.9-rc2

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Message-ID: <20200831072427.GM1362448@hirez.programming.kicks-ass.net>
Date:   Mon, 31 Aug 2020 09:24:27 +0200
From:   peterz@...radead.org
To:     Linus Torvalds <torvalds@...ux-foundation.org>
Cc:     Thomas Gleixner <tglx@...utronix.de>,
        Marco Elver <elver@...gle.com>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        "the arch/x86 maintainers" <x86@...nel.org>
Subject: Re: [GIT pull] sched/urgent for v5.9-rc2

On Sun, Aug 30, 2020 at 11:54:19AM -0700, Linus Torvalds wrote:
> On Sun, Aug 30, 2020 at 11:04 AM Thomas Gleixner <tglx@...utronix.de> wrote:
> >
> >  - Make is_idle_task() __always_inline to prevent the compiler from putting
> >    it out of line into the wrong section because it's used inside noinstr
> >    sections.
> 
> What completely broken compiler uninlined that single-instruction function?
> 
> I've obviously pulled this, but it sounds like there should be a
> compiler bug-report for this insane behavior.
> 
> Or is Marco building the kernel without optimizations or something
> like that? That has not been a supported model, for various good
> reasons..

I think that was Clang with KCSAN on, KCSAN obviously makes this
function a little bigger with the instrumentation for the load(s). But
yes...