linux-kernel - Re: [PATCH] freezer vs stopped or traced

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Message-ID: <20080304221920.GB7646@elf.ucw.cz>
Date:	Tue, 4 Mar 2008 23:19:20 +0100
From:	Pavel Machek <pavel@....cz>
To:	"Rafael J. Wysocki" <rjw@...k.pl>
Cc:	Roland McGrath <roland@...hat.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	linux-pm@...ts.linux-foundation.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] freezer vs stopped or traced

Hi!

> > This changes the "freezer" code used by suspend/hibernate in its treatment
> > of tasks in TASK_STOPPED (job control stop) and TASK_TRACED (ptrace) states.
> > 
> > As I understand it, the intent of the "freezer" is to hold all tasks
> > from doing anything significant.  For this purpose, TASK_STOPPED and
> > TASK_TRACED are "frozen enough".  It's possible the tasks might resume
> > from ptrace calls (if the tracer were unfrozen) or from signals
> > (including ones that could come via timer interrupts, etc).  But this
> > doesn't matter as long as they quickly block again while "freezing" is
> > in effect.  Some minor adjustments to the signal.c code make sure that
> > try_to_freeze() very shortly follows all wakeups from both kinds of
> > stop.  This lets the freezer code safely leave stopped tasks unmolested.
> > 
> > Changing this fixes the longstanding bug of seeing after resuming from
> > suspend/hibernate your shell report "[1] Stopped" and the like for all
> > your jobs stopped by ^Z et al, as if you had freshly fg'd and ^Z'd them.
> > It also removes from the freezer the arcane special case treatment for
> > ptrace'd tasks, which relied on intimate knowledge of ptrace
> > internals.

I'm glad someone who actually understands signal code got to look at
this ;-). The patch looks okay to me, but I can't say I'm too
qualified in this area.

...but this is 2.6.26 material, right?
								Pavel
-- 
(english) http://www.livejournal.com/~pavelmachek
(cesky, pictures) http://atrey.karlin.mff.cuni.cz/~pavel/picture/horses/blog.html
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