linux-kernel - Re: [Patch V0] x86, mce: Ensure offline CPU's don't participate in mce rendezvous process.

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Message-ID: <CALCETrVw+iYyemu1tEDhRkYc5uTL0E9rvM-2uVeXyrcpvEjGgQ@mail.gmail.com>
Date:	Fri, 4 Dec 2015 14:34:52 -0800
From:	Andy Lutomirski <luto@...capital.net>
To:	"Luck, Tony" <tony.luck@...el.com>
Cc:	Borislav Petkov <bp@...en8.de>, "Raj, Ashok" <ashok.raj@...el.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"linux-edac@...r.kernel.org" <linux-edac@...r.kernel.org>
Subject: Re: [Patch V0] x86, mce: Ensure offline CPU's don't participate in
 mce rendezvous process.

On Fri, Dec 4, 2015 at 9:53 AM, Luck, Tony <tony.luck@...el.com> wrote:
>> I don't mean that - I mean the stuff we do before we call
>> cpu_is_offline() like ist_enter, this_cpu_inc(mce_exception_count),
>> etc. Then we do a whole another bunch of stuff at the "out:" label like
>> printk and whatnot which shouldn't run on an offlined CPU.
>
> ist_enter() is black magic to me. Andy? Would you be worried about executing
> ist_{enter,exit}() on a cpu that was once online, but is currently marked offline
> by Linux?

Offline CPUs are black magic to me.  But as long as the CPU works the
way that the normal specs say it should, then ist_enter is fair game.
In any event, if context tracking blows up on an offline CPU, I'd
argue that's a context tracking bug and needs to be fixed.

But maybe offlined CPUs are supposed to have all interrupts off
(including MCE?) and the argument goes the other way?  Dunno.

--Andy
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