linux-kernel - Re: [RFC PATCH 9/9] livepatch: update task universe when exiting kernel

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Message-ID: <20150217145830.GD11861@treble.redhat.com>
Date:	Tue, 17 Feb 2015 08:58:30 -0600
From:	Josh Poimboeuf <jpoimboe@...hat.com>
To:	Jiri Slaby <jslaby@...e.cz>
Cc:	Seth Jennings <sjenning@...hat.com>, Jiri Kosina <jkosina@...e.cz>,
	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 9/9] livepatch: update task universe when exiting
 kernel

On Mon, Feb 16, 2015 at 11:16:11AM +0100, Jiri Slaby wrote:
> On 02/09/2015, 06:31 PM, Josh Poimboeuf wrote:
> > Update a tasks's universe when returning from a system call or user
> > space interrupt, or after handling a signal.
> > 
> > This greatly increases the chances of a patch operation succeeding.  If
> > a task is I/O bound, it can switch universes when returning from a
> > system call.  If a task is CPU bound, it can switch universes when
> > returning from an interrupt.  If a task is sleeping on a to-be-patched
> > function, the user can send SIGSTOP and SIGCONT to force it to switch.
> > 
> > Since the idle "swapper" tasks don't ever exit the kernel, they're
> > updated from within the idle loop.
> > 
> > Signed-off-by: Josh Poimboeuf <jpoimboe@...hat.com>
> > ---
> >  arch/x86/include/asm/thread_info.h |  4 +++-
> >  arch/x86/kernel/signal.c           |  4 ++++
> >  include/linux/livepatch.h          |  2 ++
> >  kernel/livepatch/transition.c      | 15 +++++++++++++++
> >  kernel/sched/idle.c                |  4 ++++
> ...
> > --- a/kernel/sched/idle.c
> > +++ b/kernel/sched/idle.c
> > @@ -7,6 +7,7 @@
> >  #include <linux/tick.h>
> >  #include <linux/mm.h>
> >  #include <linux/stackprotector.h>
> > +#include <linux/livepatch.h>
> >  
> >  #include <asm/tlb.h>
> >  
> > @@ -250,6 +251,9 @@ static void cpu_idle_loop(void)
> >  
> >  		sched_ttwu_pending();
> >  		schedule_preempt_disabled();
> > +
> > +		if (unlikely(test_thread_flag(TIF_KLP_NEED_UPDATE)))
> > +			klp_update_task_universe(current);
> 
> Oh, this is indeed broken on non-x86 archs as kbuild reports.
> (TIF_KLP_NEED_UPDATE undefined)
> 
> We need a klp_maybe_update_task_universe inline or something like that
> and define it void for non-LIVEPATCH configs.

Doh, thanks.

-- 
Josh
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