Re: [RFC 09/16] kgr: mark task_safe in some kthreads

From: Jiri Kosina <jkosina@suse.cz>
To: Tejun Heo <tj@kernel.org>
Cc: Jiri Slaby <jslaby@suse.cz>,
	linux-kernel@vger.kernel.org, jirislaby@gmail.com,
	Vojtech Pavlik <vojtech@suse.cz>, Michael Matz <matz@suse.de>,
	Steven Rostedt <rostedt@goodmis.org>,
	Frederic Weisbecker <fweisbec@gmail.com>,
	Ingo Molnar <mingo@redhat.com>,
	Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
	"Theodore Ts'o" <tytso@mit.edu>,
	Dipankar Sarma <dipankar@in.ibm.com>,
	"Paul E. McKenney" <paulmck@linux.vnet.ibm.com>
Subject: Re: [RFC 09/16] kgr: mark task_safe in some kthreads
Date: Thu, 1 May 2014 22:17:44 +0200 (CEST)	[thread overview]
Message-ID: <alpine.LNX.2.00.1405012206430.29834@pobox.suse.cz> (raw)
In-Reply-To: <20140501142414.GA31611@htj.dyndns.org>

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