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

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Date:	Fri, 4 Dec 2015 19:00:01 +0100
From:	Borislav Petkov <bp@...en8.de>
To:	"Luck, Tony" <tony.luck@...el.com>
Cc:	"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>,
	"Andy Lutomirski (luto@...capital.net)" <luto@...capital.net>
Subject: Re: [Patch V0] x86, mce: Ensure offline CPU's don't participate in
 mce rendezvous process.

On Fri, Dec 04, 2015 at 05:53:33PM +0000, Luck, Tony 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?

ist_enter() is context tracking functionality.

> Bumping mce_exception_count doesn't look like a big deal either way. It is visible in
> /proc/interrupts so I'd like to keep that honest (if the cpu comes back online again).
> But we could do the offline check before this.
> 
> There will be no printk() executed in the tail of the function. after we clear MCG_STATUS
> at the (new location of) the out: label we will see recover_paddr is still ~0ull and "goto done".

Whether it is kosher or not is beside the point. Why should an offlined
CPU even noodle through all that code if it doesn't need/have to? It can
return immediately instead.

-- 
Regards/Gruss,
    Boris.

ECO tip #101: Trim your mails when you reply.
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