linux-kernel - Re: sched: horrible way to detect whether a task has been preempted

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Message-ID: <alpine.LNX.2.00.1604080904290.27368@cbobk.fhfr.pm>
Date:	Fri, 8 Apr 2016 09:05:28 +0200 (CEST)
From:	Jiri Kosina <jikos@...nel.org>
To:	Jessica Yu <jeyu@...hat.com>
cc:	Josh Poimboeuf <jpoimboe@...hat.com>,
	Miroslav Benes <mbenes@...e.cz>, linux-kernel@...r.kernel.org,
	live-patching@...r.kernel.org, Vojtech Pavlik <vojtech@...e.com>
Subject: Re: sched: horrible way to detect whether a task has been
 preempted

On Thu, 7 Apr 2016, Jessica Yu wrote:

> > Alternatively, without eating up a TIF_ space, it'd be possible to push a
> > magic contents on top of the stack in preempt_schedule_irq() (and pop it
> > once we are returning from there), and if such magic value is detected, we
> > just don't bother and claim unreliability.
> 
> Ah, but wouldn't we still have to walk through the frames (i.e. enter
> the loop in patch 7/14) to look for the magic value in this approach?

The idea was that it'd be located at a place to which saved stack pointer 
of the sleeping task is pointing to (or at a fixed offset from it).

-- 
Jiri Kosina
SUSE Labs