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From:   Marco Elver <elver@google.com>
Date:   Mon, 31 Aug 2020 09:38:28 +0200
Message-ID: <CANpmjNP5xPUqkBfR2xu8KvDJeo6Vc2HM46HnBfhgA+asV0dm+A@mail.gmail.com>
Subject: Re: [GIT pull] sched/urgent for v5.9-rc2
To:     Peter Zijlstra <peterz@infradead.org>
Cc:     Linus Torvalds <torvalds@linux-foundation.org>,
        Thomas Gleixner <tglx@linutronix.de>,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
        "the arch/x86 maintainers" <x86@kernel.org>
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On Mon, 31 Aug 2020 at 09:24, <peterz@infradead.org> wrote:
>
> 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@linutronix.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...

I wasn't quite sure myself if it was Clang or GCC, so I re-tested with
the linked config (which says GCC), and it reproduces on both.