linux-kernel - Re: [PATCH] x86/apic: Fix circular locking dependency between console and hrtimer locks

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Date:   Mon, 27 Apr 2020 18:54:10 +0300
From:   Leon Romanovsky <leon@...nel.org>
To:     Thomas Gleixner <tglx@...utronix.de>
Cc:     Ingo Molnar <mingo@...nel.org>, Ingo Molnar <mingo@...hat.com>,
        Borislav Petkov <bp@...en8.de>,
        "H. Peter Anvin" <hpa@...or.com>, x86 <x86@...nel.org>,
        Suresh Siddha <suresh.b.siddha@...el.com>,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] x86/apic: Fix circular locking dependency between
 console and hrtimer locks

On Mon, Apr 27, 2020 at 05:31:21PM +0200, Thomas Gleixner wrote:
> Leon Romanovsky <leon@...nel.org> writes:
> > OK, I consulted with verification people and back then the trigger was:
> > Reproduce when run "echo 1 > /sys/kernel/debug/clear_warn_once" after
> > reboot
>
> That explains it.
>
> > [    0.937310] Freeing SMP alternatives memory: 32K
> > [    0.940471] TSC deadline timer enabled
>
> So here is the first one which sets 'once'. Of course if you clear 'once'
> afterwards then this triggers because the context is completely
> different.
>
> So the right thing to do is to move this out of __setup_APIC_LVTT() and
> be done with it.

Thanks a lot.