linux-kernel - Re: [PATCH 1/8] Enhance process freezer interface for usage beyond software suspend

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Date:	Fri, 6 Apr 2007 16:34:49 +0200
From:	"Rafael J. Wysocki" <rjw@...k.pl>
To:	Pavel Machek <pavel@....cz>
Cc:	Gautham R Shenoy <ego@...ibm.com>, akpm@...ux-foundation.org,
	paulmck@...ibm.com, torvalds@...ux-foundation.org,
	linux-kernel@...r.kernel.org, vatsa@...ibm.com,
	Oleg Nesterov <oleg@...sign.ru>, mingo@...e.hu,
	dipankar@...ibm.com, dino@...ibm.com,
	masami.hiramatsu.pt@...achi.com
Subject: Re: [PATCH 1/8] Enhance process freezer interface for usage beyond software suspend

On Monday, 2 April 2007 22:51, Pavel Machek wrote:
> Hi!
> 
> > > > +/* Per process freezer specific flags */
> > > > +#define PF_FE_SUSPEND	0x00008000	/* This thread should not be frozen
> > > > +					 * for suspend
> > > > +					 */
> > > > +
> > > > +#define PF_FE_KPROBES	0x00000010	/* This thread should not be frozen
> > > > +					 * for Kprobes
> > > > +					 */
> > > 
> > > Just put the comment before the define for long comments?
> > 
> > Agreed.
> 
> (Actually it would be nice to say
> 
> /* This thread should not be frozen for suspend, becuase it is needed
>    for getting image saved to disk */
> 
> > > > -#ifdef CONFIG_PM
> > > > +#if defined(CONFIG_PM) || defined(CONFIG_HOTPLUG_CPU) || \
> > > > +					defined(CONFIG_KPROBES)
> > > 
> > > Should we create CONFIG_FREEZER?
> > 
> > Why do you think so?  I think the freezer should be compiled automatically
> > if any of the above is set, which is what this directive really means.
> 
> Kconfig can do that. ("select statement"). If we have one such ifdef,
> it is okay, but if it would be more of them.
> 
> > > Hmmm, I do not really like softlockup watchdog running during suspend.
> > > Can we make this freezeable and make watchdog shut itself off while
> > > suspending?
> > 
> > Generally, I agree, but this patch only replaces the existing instances
> > of PF_NOFREEZE with the new mechanism.  The changes you're talking about
> > require a separate patch series (or at least one separate patch), I think, and
> > they need not be so simple to make.
> 
> Agreed about separate patch series.
> 
> > > > -	current->flags |= PF_NOFREEZE;
> > > > +	freezer_exempt(FE_ALL);
> > > >  	pid = kernel_thread(do_linuxrc, "/linuxrc", SIGCHLD);
> > > >  	if (pid > 0) {
> > > >  		while (pid != sys_wait4(-1, NULL, 0, NULL))
> > > 
> > > Does this mean we have userland /linuxrc running with PF_NOFREEZE?
> > > That would be very bad...
> > 
> > No, actually it is _required_ for the userland resume to work.  Well, perhaps
> > I should place a comment in there so that I don't have to explain this again
> > and again. :-)
> 
> Can you put big bold comment there?
>
> Why is it needed? Freezer never freezes _current_ task.

No, it doesn't, but this task spawns linuxrc and then calls sys_wait4() in a
loop.

Well, actually, I'll try to plant try_to_freeze() in this loop and see if that
works.  If it doesn't, I'll add a comment.

> > > > @@ -104,7 +104,7 @@ static int __kprobes check_safety(void)
> > > >  {
> > > >  	int ret = 0;
> > > >  #if defined(CONFIG_PREEMPT) && defined(CONFIG_PM)
> > > 
> > > Eh? Why does kprobes code depend on config_pm?
> > 
> > Because it uses the freezer? ;-)
> 
> That is no longer true after this patch... Ugly ifdef above makes sure
> freezer is there for kprobes. I'm trying to say that #if above is
> now broken. Actually it was probably always broken, but it just became
> more so.

Agreed.

Greetings,
Rafael
-
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/