linux-kernel - Re: [RFC PATCH v1.9 14/14] livepatch: update task universe when exiting kernel

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Message-ID: <20160414133951.eydmvevb65jzse5e@treble>
Date:	Thu, 14 Apr 2016 08:39:51 -0500
From:	Josh Poimboeuf <jpoimboe@...hat.com>
To:	Miroslav Benes <mbenes@...e.cz>
Cc:	Jiri Kosina <jikos@...nel.org>, Jessica Yu <jeyu@...hat.com>,
	linux-kernel@...r.kernel.org, live-patching@...r.kernel.org,
	Vojtech Pavlik <vojtech@...e.com>
Subject: Re: [RFC PATCH v1.9 14/14] livepatch: update task universe when
 exiting kernel

On Thu, Apr 14, 2016 at 10:50:28AM +0200, Miroslav Benes wrote:
> On Thu, 14 Apr 2016, Miroslav Benes wrote:
> 
> > On Fri, 25 Mar 2016, 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.
> > 
> > Well, I am still not familiarized enough with Andy's recent rework of 
> > entry stuff, but I think all of this is correct. Maybe I would add 
> > a note to the changelog, that since TIF_KLP_NEED_UPDATE is defined 14th 
> > bit it is also automatically included in _TIF_ALLWORK_MASKS. 
> 
> And I forgot to add that I would try to prepare similar thing for s390 and 
> maybe powerpc (taking recent development there into account). That's gonna 
> be fun :)

Yeah, good point.  I've glanced at the entry code for both architectures
and I don't think it'll be too bad, though the devil's in the details.

-- 
Josh