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Message-Id: <200705282017.51210.rjw@sisk.pl>
Date: Mon, 28 May 2007 20:17:50 +0200
From: "Rafael J. Wysocki" <rjw@...k.pl>
To: nigel@...el.suspend2.net
Cc: LKML <linux-kernel@...r.kernel.org>,
Andrew Morton <akpm@...ux-foundation.org>,
Gautham R Shenoy <ego@...ibm.com>,
Linus Torvalds <torvalds@...ux-foundation.org>,
Oleg Nesterov <oleg@...sign.ru>, Pavel Machek <pavel@....cz>
Subject: Re: [RFC][PATCH][EXPERIMENTAL] Make kernel threads nonfreezable by default
On Monday, 28 May 2007 11:46, Nigel Cunningham wrote:
> Hello!
>
> In reply to your more recent message, I had looked but not tried, so
> didn't feel in a position to reply yet.
>
> On Sun, 2007-05-27 at 00:12 +0200, Rafael J. Wysocki wrote:
> > 63 files changed, 78 insertions(+), 138 deletions(-)
>
> Well, that looks good, for a start :)
>
> > Index: linux-2.6.22-rc3/kernel/exit.c
> > ===================================================================
> > --- linux-2.6.22-rc3.orig/kernel/exit.c
> > +++ linux-2.6.22-rc3/kernel/exit.c
> > @@ -389,6 +389,11 @@ void daemonize(const char *name, ...)
> > * they would be locked into memory.
> > */
> > exit_mm(current);
> > + /*
> > + * We don't want to have TIF_FREEZE set if the system-wide hibernation
> > + * or suspend transision begins right now.
> > + */
> > + current->flags |= PF_NOFREEZE;
>
> s/transision/transition
Thanks, will fix.
> > set_special_pids(1, 1);
> > proc_clear_tty(current);
> > Index: linux-2.6.22-rc3/include/linux/freezer.h
> > ===================================================================
> > --- linux-2.6.22-rc3.orig/include/linux/freezer.h
> > +++ linux-2.6.22-rc3/include/linux/freezer.h
> > @@ -118,6 +118,14 @@ static inline int freezer_should_skip(st
> > return !!(p->flags & PF_FREEZER_SKIP);
> > }
> >
> > +/*
> > + * Tell the freezer that the current task should be frozen by it
> > + */
> > +static inline void set_freezable(void)
> > +{
> > + current->flags &= ~PF_NOFREEZE;
> > +}
> > +
>
> Given the clearing of the flag above, should we just have a
> set_unfreezeable here that's used above (and potentially elsewhere)...
> (reads more)... or more generic set_[un]freezeable(task_struct *p)
> routines that could also be used in copy_flags below?
Yes, I can introduce set_unfreezeable(), although that would be used in
a couple of places only.
I don't think it's a good idea to have set_[un]freezeable(task_struct *p),
since only current is allowed to set/unset its flags.
> > #else
> > static inline int frozen(struct task_struct *p) { return 0; }
> > static inline int freezing(struct task_struct *p) { return 0; }
> > @@ -134,6 +142,7 @@ static inline int try_to_freeze(void) {
> > static inline void freezer_do_not_count(void) {}
> > static inline void freezer_count(void) {}
> > static inline int freezer_should_skip(struct task_struct *p) { return 0; }
> > +static inline void set_freezable_current(void) {}
Ah, this is a mistake (wrong name).
> > #endif
> >
> > #endif /* LINUX_FREEZER_H */
> > Index: linux-2.6.22-rc3/kernel/fork.c
> > ===================================================================
> > --- linux-2.6.22-rc3.orig/kernel/fork.c
> > +++ linux-2.6.22-rc3/kernel/fork.c
> > @@ -920,7 +920,7 @@ static inline void copy_flags(unsigned l
> > {
> > unsigned long new_flags = p->flags;
> >
> > - new_flags &= ~(PF_SUPERPRIV | PF_NOFREEZE);
> > + new_flags &= ~PF_SUPERPRIV;
> > new_flags |= PF_FORKNOEXEC;
> > if (!(clone_flags & CLONE_PTRACE))
> > p->ptrace = 0;
> > Index: linux-2.6.22-rc3/arch/i386/kernel/io_apic.c
> > ===================================================================
> > --- linux-2.6.22-rc3.orig/arch/i386/kernel/io_apic.c
> > +++ linux-2.6.22-rc3/arch/i386/kernel/io_apic.c
> > @@ -669,7 +669,6 @@ static int balanced_irq(void *unused)
> >
> > for ( ; ; ) {
> > time_remaining = schedule_timeout_interruptible(time_remaining);
> > - try_to_freeze();
> > if (time_after(jiffies,
> > prev_balance_time+balanced_irq_interval)) {
> > preempt_disable();
>
> I'm the one who is confused, aren't I? If I'm reading this right,
> io_apic used to be frozen. After this patch, it will not be frozen. If
> that's the intended behaviour, shouldn't this be two patches - one to
> make kernel threads unfreezeable by default, and one to make threads
> that were formerly freezeable unfreezeable?
Yes, I think you're right. I tend to try to make too many changes in one
shot. :-)
>
> [...]
>
> > Index: linux-2.6.22-rc3/Documentation/power/swsusp.txt
> > ===================================================================
> > --- linux-2.6.22-rc3.orig/Documentation/power/swsusp.txt
> > +++ linux-2.6.22-rc3/Documentation/power/swsusp.txt
> > @@ -140,22 +140,6 @@ should be sent to the mailing list avail
> > website, and not to the Linux Kernel Mailing List. We are working
> > toward merging suspend2 into the mainline kernel.
> >
> > -Q: A kernel thread must voluntarily freeze itself (call 'refrigerator').
> > -I found some kernel threads that don't do it, and they don't freeze
> > -so the system can't sleep. Is this a known behavior?
> > -
> > -A: All such kernel threads need to be fixed, one by one. Select the
> > -place where the thread is safe to be frozen (no kernel semaphores
> > -should be held at that point and it must be safe to sleep there), and
> > -add:
> > -
> > - try_to_freeze();
> > -
> > -If the thread is needed for writing the image to storage, you should
> > -instead set the PF_NOFREEZE process flag when creating the thread (and
> > -be very careful).
> > -
> > -
> > Q: What is the difference between "platform" and "shutdown"?
> >
> > A:
>
> Perhaps it would be good to keep a variant of this question, along the
> lines of:
>
> Q: I have a kernel thread that needs to be frozen during hibernation.
> How do I make that happen?
Good idea.
Thanks for the comments.
Greetings,
Rafael
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