linux-kernel - Re: [RFC PATCH v1.9 12/14] livepatch: create per-task consistency model

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Date:	Mon, 4 Apr 2016 13:33:07 -0500
From:	Josh Poimboeuf <jpoimboe@...hat.com>
To:	Vojtech Pavlik <vojtech@...e.com>
Cc:	Miroslav Benes <mbenes@...e.cz>, Jiri Kosina <jikos@...nel.org>,
	Jessica Yu <jeyu@...hat.com>, linux-kernel@...r.kernel.org,
	live-patching@...r.kernel.org
Subject: Re: [RFC PATCH v1.9 12/14] livepatch: create per-task consistency
 model

On Mon, Apr 04, 2016 at 08:27:59PM +0200, Vojtech Pavlik wrote:
> On Mon, Apr 04, 2016 at 01:21:38PM -0500, Josh Poimboeuf wrote:
> 
> > Hm, can you explain why it should be copied from the parent?
> > 
> > I'm thinking the above code is correct for today, but it should still be
> > changed to be more future-proof.
> > 
> > Here's my thinking:
> > 
> > A forked task starts out with no stack, so if I understand correctly, it
> > can safely start out in the goal universe, regardless of which universe
> > its parent belongs to.
> > 
> > However, the current ret_from_fork code is a mess, and Andy Lutomirski
> > has mentioned that he would like to give newly forked tasks a proper
> > stack such that instead of jumping to ret_from_fork, they would just
> > return from schedule().  In that case, it would no longer be safe to
> > start the new task in the goal universe because it could be "sleeping"
> > on a to-be-patched function.
> > 
> > So for proper future proofing, newly forked tasks should be started in
> > the initial universe (rather than starting in the goal universe or
> > inheriting the parent's universe).  They can then be transitioned over
> > to the goal universe like any other task.  How does that sound?
> 
> How could a newly forked task start in the old universe if its parent
> has already been migrated? Any context it inherits will already be from
> the new universe.

Can you be more specific about "context" and why inheritance of it would
be a problem?

-- 
Josh