linux-kernel - Re: smp_call_function

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Message-ID: <CA+55aFyepTTiBoRr1xuc7uVLrdK8ug59sWgQiT7CVm8-oCHJJw@mail.gmail.com>
Date:	Thu, 2 Apr 2015 10:35:43 -0700
From:	Linus Torvalds <torvalds@...ux-foundation.org>
To:	Ingo Molnar <mingo@...nel.org>
Cc:	Chris J Arges <chris.j.arges@...onical.com>,
	Rafael David Tinoco <inaddy@...ntu.com>,
	Peter Anvin <hpa@...or.com>,
	Jiang Liu <jiang.liu@...ux.intel.com>,
	Peter Zijlstra <peterz@...radead.org>,
	LKML <linux-kernel@...r.kernel.org>,
	Jens Axboe <axboe@...nel.dk>,
	Frederic Weisbecker <fweisbec@...il.com>,
	Gema Gomez <gema.gomez-solano@...onical.com>,
	"the arch/x86 maintainers" <x86@...nel.org>
Subject: Re: smp_call_function_single lockups

On Thu, Apr 2, 2015 at 2:55 AM, Ingo Molnar <mingo@...nel.org> wrote:
>
> So another possibility would be that it's the third change causing
> this change in behavior:

Oh, yes, that looks much more likely. I overlooked that small change entirely.

> ... since with this we won't send IPIs in a semi-nested fashion with
> an unacked APIC, which is a good idea to do in general. It's also a
> weird enough hardware pattern that virtualization's APIC emulation
> might get it slightly wrong or slightly different.

Yup, that's more likely than the subtle timing/reordering differences
of just the added debug printouts. I agree.

                             Linus
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