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SubjectRe: [PATCH 1/8] Enhance process freezer interface for usage beyond software suspend
Date
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@in.ibm.com>
> > Cc: Pavel Machek <pavel@ucw.cz>
> > Cc: Rafael J. Wysocki <rjw@sisk.pl>
> > Cc: Masami Hiramatsu <masami.hiramatsu.pt@hitachi.com>
>
> Actually no, I was not in cc.
>
> > +/* 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.

> > -#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, &param);
> > - 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.

> > 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? ;-)

Greetings,
Rafael
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