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

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Date:	Tue, 10 Feb 2015 09:57:44 +0100 (CET)
From:	Jiri Kosina <jkosina@...e.cz>
To:	Josh Poimboeuf <jpoimboe@...hat.com>
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 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?

-- 
Jiri Kosina
SUSE Labs
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