linux-kernel - Re: [RFC 09/16] kgr: mark task

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Message-ID: <alpine.LNX.2.00.1405012206430.29834@pobox.suse.cz>
Date:	Thu, 1 May 2014 22:17:44 +0200 (CEST)
From:	Jiri Kosina <jkosina@...e.cz>
To:	Tejun Heo <tj@...nel.org>
cc:	Jiri Slaby <jslaby@...e.cz>, linux-kernel@...r.kernel.org,
	jirislaby@...il.com, Vojtech Pavlik <vojtech@...e.cz>,
	Michael Matz <matz@...e.de>,
	Steven Rostedt <rostedt@...dmis.org>,
	Frederic Weisbecker <fweisbec@...il.com>,
	Ingo Molnar <mingo@...hat.com>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	Theodore Ts'o <tytso@....edu>,
	Dipankar Sarma <dipankar@...ibm.com>,
	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
Subject: Re: [RFC 09/16] kgr: mark task_safe in some kthreads

On Thu, 1 May 2014, Tejun Heo wrote:

> > Some threads do not use kthread_should_stop. Before we enable a
> 
> Haven't really following kgraft development but is it safe to assume
> that all kthread_should_stop() usages are clean side-effect-less
> boundaries?  If so, why is that property guaranteed?  Is there any
> mechanism for sanity checks?  Maybe I'm just failing to understand how
> the whole thing is supposed to work but this looks like it could
> devolve into something more broken than the freezer which we haven't
> fully recovered from yet.

Hi Tejun,

first, thanks a lot for review.

I agree that this expectation might really somewhat implicit and is not 
probably properly documented anywhere. The basic observation is "whenever 
kthread_should_stop() is being called, all data structures are in a 
consistent state and don't need any further updates in order to achieve 
consistency, because we can exit the loop immediately here", as 
kthread_should_stop() is the very last thing every freezable kernel thread 
is calling before starting a new iteration.

For the sake of collecting data points -- do you happen to have any 
counter-example to the assumption?

Thanks,

-- 
Jiri Kosina
SUSE Labs
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