linux-kernel - Re: [RFC PATCH v1.9 05/14] sched: horrible way to detect whether a task has been preempted

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Date:	Fri, 8 Apr 2016 09:34:33 -0500
From:	Josh Poimboeuf <jpoimboe@...hat.com>
To:	Petr Mladek <pmladek@...e.com>
Cc:	Jiri Kosina <jikos@...nel.org>, Jessica Yu <jeyu@...hat.com>,
	Miroslav Benes <mbenes@...e.cz>, linux-kernel@...r.kernel.org,
	live-patching@...r.kernel.org, Vojtech Pavlik <vojtech@...e.com>
Subject: Re: [RFC PATCH v1.9 05/14] sched: horrible way to detect whether a
 task has been preempted

On Fri, Apr 08, 2016 at 10:07:10AM +0200, Petr Mladek wrote:
> On Thu 2016-04-07 09:34:03, Josh Poimboeuf wrote:
> > On Thu, Apr 07, 2016 at 11:47:00AM +0200, Petr Mladek wrote:
> > > On Wed 2016-04-06 11:33:56, Josh Poimboeuf wrote:
> > > > On Wed, Apr 06, 2016 at 03:06:19PM +0200, Petr Mladek wrote:
> > > We could even move this check into the livepatch code but then
> > > print_context_stack_reliable() will not always give reliable results.
> > 
> > Why would moving the check to the livepatch code affect the reliability
> > of print_context_stack_reliable()?
> 
> print_context_stack_reliable() is a generic function that might
> eventualy be used also outside livepatch code. If there is
> preempt_schedule_irq() on the stack, it means that the rest
> of the stack might be unreliable and it should be detected
> by the function itself.

Ah, I see now.  I actually thought you meant something else (moving
in_preempt_schedule_irq() itself to livepatch code, but still calling it
from print_context_stack_reliable()).

> Let's forget the idea of moving the check into the livepatch
> code :-)

Agreed :-)

-- 
Josh