linux-kernel - Re: [RFC PATCH 0/9] livepatch: consistency model

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Date:	Tue, 10 Feb 2015 08:43:30 -0600
From:	Josh Poimboeuf <jpoimboe@...hat.com>
To:	Jiri Kosina <jkosina@...e.cz>
Cc:	Seth Jennings <sjenning@...hat.com>,
	Vojtech Pavlik <vojtech@...e.cz>,
	Masami Hiramatsu <masami.hiramatsu.pt@...achi.com>,
	live-patching@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [RFC PATCH 0/9] livepatch: consistency model

On Tue, Feb 10, 2015 at 09:57:44AM +0100, Jiri Kosina wrote:
> On Mon, 9 Feb 2015, Josh Poimboeuf wrote:
> 
> > 2) As mentioned above, kthreads which are always sleeping on a patched function
> >    will never transition to the new universe.  This is really a minor issue
> >    (less than 1% of patches).  It's not necessarily something that needs to be
> >    resolved with this patch set, but it would be good to have some discussion
> >    about it regardless.
> >    
> >    To overcome this issue, I have 1/2 an idea: we could add some stack checking
> >    code to the ftrace handler itself to transition the kthread to the new
> >    universe after it re-enters the function it was originally sleeping on, if
> >    the stack doesn't already have have any other to-be-patched functions.
> >    Combined with the klp_transition_work_fn()'s periodic stack checking of
> >    sleeping tasks, that would handle most of the cases (except when trying to
> >    patch the high-level thread_fn itself).
> > 
> >    But then how do you make the kthread wake up?  As far as I can tell,
> >    wake_up_process() doesn't seem to work on a kthread (unless I messed up my
> >    testing somehow).  What does kGraft do in this case?
> 
> wake_up_process() really should work for (p->flags & PF_KTHREAD) 
> task_struct. What was your testing scenario?

Hm, I probably did something stupid.  I'll try it again :-)

-- 
Josh
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