linux-kernel - RE: livepatch: change to a per-task consistency model

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Message-ID: <alpine.LNX.2.00.1605250042020.31937@cbobk.fhfr.pm>
Date:	Wed, 25 May 2016 00:45:05 +0200 (CEST)
From:	Jiri Kosina <jikos@...nel.org>
To:	David Laight <David.Laight@...LAB.COM>
cc:	Josh Poimboeuf <jpoimboe@...hat.com>,
	"linux-s390@...r.kernel.org" <linux-s390@...r.kernel.org>,
	Jessica Yu <jeyu@...hat.com>,
	Vojtech Pavlik <vojtech@...e.com>,
	Petr Mladek <pmladek@...e.com>,
	Peter Zijlstra <peterz@...radead.org>,
	"x86@...nel.org" <x86@...nel.org>,
	Heiko Carstens <heiko.carstens@...ibm.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Ingo Molnar <mingo@...hat.com>,
	Andy Lutomirski <luto@...nel.org>,
	"live-patching@...r.kernel.org" <live-patching@...r.kernel.org>,
	Jiri Slaby <jslaby@...e.cz>, Miroslav Benes <mbenes@...e.cz>,
	"linuxppc-dev@...ts.ozlabs.org" <linuxppc-dev@...ts.ozlabs.org>,
	Chris J Arges <chris.j.arges@...onical.com>
Subject: RE: livepatch: change to a per-task consistency model

On Tue, 24 May 2016, David Laight wrote:

> > > Related, please can we have a flag for the sleep and/or process so that
> > > an uninterruptible sleep doesn't trigger the 'hung task' detector
> > 
> > TASK_KILLABLE
> 
> Not sure that does what I want.
> It appears to allow some 'kill' actions to wake the process.
> I'm sure I've looked at the 'hung task' code since 2007.

The trick is the 

	if (t->state == TASK_UNINTERRUPTIBLE)

test in check_hung_uninterruptible_tasks(). That makes sure that 
TASK_KILLABLE tasks (e.g. waiting on NFS I/O, but not limited only to 
that; feel free to set it whereever you need) are skipped. Please note 
that TASK_KILLABLE is actually a _mask_ that includes TASK_UNINTERRUPTIBLE 
as well; therefore the '==' test skips such tasks.

-- 
Jiri Kosina
SUSE Labs