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Message-ID: <20070403075939.GA29308@in.ibm.com>
Date: Tue, 3 Apr 2007 13:29:39 +0530
From: Gautham R Shenoy <ego@...ibm.com>
To: "Rafael J. Wysocki" <rjw@...k.pl>
Cc: Pavel Machek <pavel@....cz>, 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 Mon, Apr 02, 2007 at 10:48:24PM +0200, Rafael J. Wysocki wrote:
> On Monday, 2 April 2007 15:56, Pavel Machek wrote:
> > Hi!
> >
> > > This patch provides an interface to extend the use of the process
> > > freezer beyond Suspend.
> > >
> > > The tasks can selectively mark themselves to be exempted from specific
> > > freeze events like SUSPEND /KPROBES/CPU_HOTPLUG.
> > >
> > > This patch however, *does not* sort non freezable threads into
> > > different categories based on the freeze events. Thus all
> > > tasks which were previously marked PF_NOFREEZE are now
> > > exempted from freezer using
> > > freezer_exempt(FE_ALL);
> > > which means exempt from all kinds of freezes.
> > >
> > > Signed-off-by: Gautham R Shenoy <ego@...ibm.com>
> > > Cc: Pavel Machek <pavel@....cz>
> > > Cc: Rafael J. Wysocki <rjw@...k.pl>
> > > Cc: Masami Hiramatsu <masami.hiramatsu.pt@...achi.com>
> >
> > Actually no, I was not in cc.
Oops! Sorry. I knew I had missed something.
> >
> > > +/* 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.
ok, Will do.
>
> > > -#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.
>
> > > Index: linux-2.6.21-rc5/kernel/softlockup.c
> > > ===================================================================
> > > --- linux-2.6.21-rc5.orig/kernel/softlockup.c
> > > +++ linux-2.6.21-rc5/kernel/softlockup.c
> > > @@ -96,7 +96,7 @@ static int watchdog(void * __bind_cpu)
> > > struct sched_param param = { .sched_priority = MAX_RT_PRIO-1 };
> > >
> > > sched_setscheduler(current, SCHED_FIFO, ¶m);
> > > - current->flags |= PF_NOFREEZE;
> > > + freezer_exempt(FE_ALL);
> > >
> > > /*
> > > * Run briefly once per second to reset the softlockup timestamp.
> >
> > 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.
Yes.
>
> > > Index: linux-2.6.21-rc5/kernel/rcutorture.c
> > > ===================================================================
> > > --- linux-2.6.21-rc5.orig/kernel/rcutorture.c
> > > +++ linux-2.6.21-rc5/kernel/rcutorture.c
> > > @@ -559,7 +559,7 @@ rcu_torture_fakewriter(void *arg)
> > >
> > > VERBOSE_PRINTK_STRING("rcu_torture_fakewriter task started");
> > > set_user_nice(current, 19);
> > > - current->flags |= PF_NOFREEZE;
> > > + freezer_exempt(FE_ALL);
> >
> >
> > Fix rcutorture instead. It has no business running while suspending.
> >
> > >
> > > do {
> > > schedule_timeout_uninterruptible(1 + rcu_random(&rand)%10);
> > > @@ -590,7 +590,7 @@ rcu_torture_reader(void *arg)
> > >
> > > VERBOSE_PRINTK_STRING("rcu_torture_reader task started");
> > > set_user_nice(current, 19);
> > > - current->flags |= PF_NOFREEZE;
> > > + freezer_exempt(FE_ALL);
> > >
> >
> > Same here.
> >
> > Eventually, we should fix apm, too.
> >
> > > Index: linux-2.6.21-rc5/init/do_mounts_initrd.c
> > > ===================================================================
> > > --- linux-2.6.21-rc5.orig/init/do_mounts_initrd.c
> > > +++ linux-2.6.21-rc5/init/do_mounts_initrd.c
> > > @@ -55,7 +55,7 @@ static void __init handle_initrd(void)
> > > sys_mount(".", "/", NULL, MS_MOVE, NULL);
> > > sys_chroot(".");
> > >
> > > - 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. :-)
>
> > > --- linux-2.6.21-rc5.orig/kernel/kprobes.c
> > > +++ linux-2.6.21-rc5/kernel/kprobes.c
> > > @@ -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? ;-)
Is that why?! Then I guess we can remove it. Because the freezer is
going to be compiled in if CONFIG_KPROBES is set.
>
> Greetings,
> Rafael
thanks
gautham.
--
Gautham R Shenoy
Linux Technology Center
IBM India.
"Freedom comes with a price tag of responsibility, which is still a bargain,
because Freedom is priceless!"
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