linux-kernel - Re: kGraft to -next [was: 00/21 kGraft]

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Date:	Wed, 2 Jul 2014 15:01:16 +0200 (CEST)
From:	Jiri Kosina <jkosina@...e.cz>
To:	One Thousand Gnomes <gnomes@...rguk.ukuu.org.uk>
cc:	Tejun Heo <tj@...nel.org>, Jiri Slaby <jslaby@...e.cz>,
	Stephen Rothwell <sfr@...b.auug.org.au>,
	linux-kernel@...r.kernel.org, rostedt@...dmis.org,
	mingo@...hat.com, akpm@...ux-foundation.org, andi@...stfloor.org,
	paulmck@...ux.vnet.ibm.com, pavel@....cz, jirislaby@...il.com,
	Vojtech Pavlik <vojtech@...e.cz>, Michael Matz <matz@...e.de>
Subject: Re: kGraft to -next [was: 00/21 kGraft]

On Wed, 2 Jul 2014, One Thousand Gnomes wrote:

> > > > https://git.kernel.org/cgit/linux/kernel/git/jirislaby/kgraft.git/log/?h=kgraft
> > > 
> > > Stephen,
> > > 
> > > may I ask you to add the kGraft tree to -next?
> > > 
> > > git://git.kernel.org/pub/scm/linux/kernel/git/jirislaby/kgraft.git#kgraft
> > 
> > Do we have consensus on the approach?  I personally really don't like
> > the fact that it's adding another aspect to kthread management which
> > is difficult to get right and nearly impossible to verify
> > automatically.
> 
> Nor me. I don't see why it can't use the kernel freeze functionality ?

Well, we are, see the patch no. 9. It all boils down basically to

[ ... ]
diff --git a/include/linux/freezer.h b/include/linux/freezer.h
index 7fd81b8c4897..e08c3bef251b 100644
--- a/include/linux/freezer.h
+++ b/include/linux/freezer.h
@@ -61,6 +61,8 @@ static inline bool try_to_freeze_unsafe(void)
 
 static inline bool try_to_freeze(void)
 {
+       kgr_task_safe(current);
+
        if (!(current->flags & PF_NOFREEZE))
                debug_check_no_locks_held();
        return try_to_freeze_unsafe();
[ ... ]


Then there are non-freezable kernel threads. We are currently handling 
those explicitly, but I agree it can be argued that they might not require 
any special handling at all, given they claimed themselves explicitly 
non-freezable.

-- 
Jiri Kosina
SUSE Labs
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