linux-kernel - Re: [BUG] msr-trace.h:42 suspicious rcu_dereference

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Message-ID: <20161130090758.afbfmuqeaiqbhvdp@pd.tnic>
Date:   Wed, 30 Nov 2016 10:07:58 +0100
From:   Borislav Petkov <bp@...en8.de>
To:     Thomas Gleixner <tglx@...utronix.de>
Cc:     Peter Zijlstra <peterz@...radead.org>,
        Steven Rostedt <rostedt@...dmis.org>,
        Jiri Olsa <jolsa@...hat.com>,
        "Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>,
        linux-kernel@...r.kernel.org, Ingo Molnar <mingo@...nel.org>,
        Josh Triplett <josh@...htriplett.org>,
        Andi Kleen <andi@...stfloor.org>,
        Jan Stancek <jstancek@...hat.com>
Subject: Re: [BUG] msr-trace.h:42 suspicious rcu_dereference_check() usage!

On Wed, Nov 30, 2016 at 09:54:58AM +0100, Thomas Gleixner wrote:
> Right, that's the safe bet. But I'm quite sure that the C1E crap only
> starts to work _after_ ACPI initialization.

Yap, I think it is an ACPI decision whether to enter C1E or not. And all
those boxes which are unaffected - they actually are but since the FW
doesn't enter C1E, they don't hit the bug.

> tick_force_broadcast() is irreversible

So if I let the cores in that small window use amd_e400_idle() and
then when I detect the machine doesn't enter C1E after all, I do
tick_broadcast_exit() on all cores in amd_e400_c1e_mask, then clear it
and free it, that would work?

Or do you see a better solution?

Thanks.

-- 
Regards/Gruss,
    Boris.

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