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From: Pavel Machek on 7 May 2008 05:40
Hi!

> From: Rafael J. Wysocki <rjw(a)sisk.pl>
>
> The freezer currently attempts to distinguish kernel threads from
> user space tasks by checking if their mm pointer is unset and it
> does not send fake signals to kernel threads. However, there are
> kernel threads, mostly related to networking, that behave like
> user space tasks and may want to be sent a fake signal to be frozen.
>
> Introduce the new process flag PF_FREEZER_NOSIG that will be set
> by default for all kernel threads and make the freezer only send
> fake signals to the tasks having PF_FREEZER_NOSIG unset. Provide
> the set_freezable_with_signal() function to be called by the kernel
> threads that want to be sent a fake signal for freezing.
>
> This patch should not change the freezer's observable behavior.
>
> Signed-off-by: Rafael J. Wysocki <rjw(a)sisk.pl>

ACK.


> -static int has_mm(struct task_struct *p)
> +static inline bool should_send_signal(struct task_struct *p)
> {
> - return (p->mm && !(p->flags & PF_BORROWED_MM));
> + return !(current->flags & PF_FREEZER_NOSIG);
> }
>

Note that we used to tell kernel threads by ->mm, and now you assume
that anything created by ktrheadd is kernel thread, ->mm or not.

I'm not sure if those can differ (->mm = NULL somewhere? Or ->mm =
something somewhere else?). I guess this should go to -mm for a long
test...

> @@ -234,7 +234,7 @@ int kthreadd(void *unused)
> set_user_nice(tsk, KTHREAD_NICE_LEVEL);
> set_cpus_allowed(tsk, CPU_MASK_ALL);
>
> - current->flags |= PF_NOFREEZE;
> + current->flags |= PF_NOFREEZE | PF_FREEZER_NOSIG;
>
> for (;;) {
> set_current_state(TASK_INTERRUPTIBLE);

Pavel
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From: Rafael J. Wysocki on 7 May 2008 08:20
On Wednesday, 7 of May 2008, Pavel Machek wrote:
> Hi!

Hi,

> > From: Rafael J. Wysocki <rjw(a)sisk.pl>
> >
> > The freezer currently attempts to distinguish kernel threads from
> > user space tasks by checking if their mm pointer is unset and it
> > does not send fake signals to kernel threads. However, there are
> > kernel threads, mostly related to networking, that behave like
> > user space tasks and may want to be sent a fake signal to be frozen.
> >
> > Introduce the new process flag PF_FREEZER_NOSIG that will be set
> > by default for all kernel threads and make the freezer only send
> > fake signals to the tasks having PF_FREEZER_NOSIG unset. Provide
> > the set_freezable_with_signal() function to be called by the kernel
> > threads that want to be sent a fake signal for freezing.
> >
> > This patch should not change the freezer's observable behavior.
> >
> > Signed-off-by: Rafael J. Wysocki <rjw(a)sisk.pl>
>
> ACK.

Thanks!

> > -static int has_mm(struct task_struct *p)
> > +static inline bool should_send_signal(struct task_struct *p)
> > {
> > - return (p->mm && !(p->flags & PF_BORROWED_MM));
> > + return !(current->flags & PF_FREEZER_NOSIG);
> > }
> >
>
> Note that we used to tell kernel threads by ->mm, and now you assume
> that anything created by ktrheadd is kernel thread, ->mm or not.
>
> I'm not sure if those can differ (->mm = NULL somewhere? Or ->mm =
> something somewhere else?).

It's done in analogy with PF_NOFREEZE, ie. everything that has
set PF_NOFREEZE by default also has PF_FREEZER_NOSIG set by default, so I
really don't expect any problems here.

> I guess this should go to -mm for a long test...

Yes, it should.

Thanks,
Rafael
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