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    SubjectRe: [RFC][PATCH][EXPERIMENTAL] Make kernel threads nonfreezable by default
    Date
    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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