linux-kernel - Re: [RFC PATCH v2 05/18] sched: add task flag for preempt IRQ tracking

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Date:	Sat, 30 Apr 2016 00:11:45 +0200 (CEST)
From:	Jiri Kosina <jikos@...nel.org>
To:	Andy Lutomirski <luto@...capital.net>
cc:	Josh Poimboeuf <jpoimboe@...hat.com>, Jessica Yu <jeyu@...hat.com>,
	Miroslav Benes <mbenes@...e.cz>,
	Ingo Molnar <mingo@...hat.com>,
	Peter Zijlstra <peterz@...radead.org>,
	Michael Ellerman <mpe@...erman.id.au>,
	Heiko Carstens <heiko.carstens@...ibm.com>,
	live-patching@...r.kernel.org,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	X86 ML <x86@...nel.org>, linuxppc-dev@...ts.ozlabs.org,
	"linux-s390@...r.kernel.org" <linux-s390@...r.kernel.org>,
	Vojtech Pavlik <vojtech@...e.com>, Jiri Slaby <jslaby@...e.cz>,
	Petr Mladek <pmladek@...e.com>,
	Chris J Arges <chris.j.arges@...onical.com>,
	Andy Lutomirski <luto@...nel.org>
Subject: Re: [RFC PATCH v2 05/18] sched: add task flag for preempt IRQ
 tracking

On Fri, 29 Apr 2016, Andy Lutomirski wrote:

> > NMI, MCE and interrupts aren't a problem because they have dedicated
> > stacks, which are easy to detect.  If the tasks' stack is on an
> > exception stack or an irq stack, we consider it unreliable.
> 
> Only on x86_64.

Well, MCEs are more or less x86-specific as well. But otherwise good 
point, thanks Andy.

So, how does stack layout generally look like in case when NMI is actually 
running on proper kernel stack? I thought it's guaranteed to contain 
pt_regs anyway in all cases. Is that not guaranteed to be the case?

Thanks,

-- 
Jiri Kosina
SUSE Labs