On 2/25/07, Rafael J. Wysocki <[email protected]> wrote:
On Sunday, 25 February 2007 15:33, Aneesh Kumar wrote:
> On 2/25/07, Rafael J. Wysocki <[email protected]> wrote:
> > On Sunday, 25 February 2007 11:45, Rafael J. Wysocki wrote:
> > > Hi,
> > >
> > > =========
> > --- linux-2.6.20-mm2.orig/kernel/power/process.c 2007-02-22 23:44:04.000000000 +0100
> > +++ linux-2.6.20-mm2/kernel/power/process.c 2007-02-23 22:33:11.000000000 +0100
> > @@ -127,22 +127,12 @@ static unsigned int try_to_freeze_tasks(
> > cancel_freezing(p);
> > continue;
> > }
> > - if (is_user_space(p)) {
> > - if (!freeze_user_space)
> > - continue;
> > -
> > - /* Freeze the task unless there is a vfork
> > - * completion pending
> > - */
> > - if (!p->vfork_done)
> > - freeze_process(p);
> > - } else {
> > - if (freeze_user_space)
> > - continue;
> > + if (is_user_space(p) == !freeze_user_space)
> > + continue;
> >
>
> How about ?
> if ( ! (is_user_space(p) == freeze_user_space) )
> continue;
I think it would be safer to do
if ( is_user_space(p) != !!freeze_user_space)
continue;
which is equivalent to my previous version, but contains one '!' more. ;-)
Seriously, the one in the patch is consistent with the other occurrences of
it in the file and I'm going to change it anyway in a separate patch
(while freezing kernel threads we need to freeze userspace tasks too in case
one of the kernel threads called kernel_execve() in the meantime).
> BTW one of the concern that vatsa had was; is it ok to allow some of
> the tasks to be left running ( the parent from vfork ) while
> freezing. I guess we can solve this in a nice way.
>
> in fork.c
>
> if (clone_flags & CLONE_VFORK) {
> p->vfork_done = &vfork;
> p->flags |= PF_PARENT_WAKEUP_ON_FREEZE;
> init_completion(&vfork);
> }
>
>
> and in freeze_process(struct task_struct *p)
>
> if ( p->flags & PF_PARENT_WAKEUP_ON_FREEZE ) {
> wake_up_parent();
> }
>
> now parent should be wating for these completion via
>
> wait_for_completion_freezable(); // pavel's implementation.
Hm, I think this leaves us with an analogous problem: we need a method
to tell a vforking task that the child should set PF_PARENT_WAKEUP_ON_FREEZE.
In the approach with PF_FREEZER_SKIP we need a method to tell the
vforking task that it should skip try_to_freeze() in freezer_count(), and I
think there are some possible ways to do this. The patch doesn't implement
any of them, because this is a different issue that can be deal with later.
But approach i outlined above make sure both parent and child get
frozen during the freeze_process. where as with PF_FREEZER_SKIP the
child waits in the completion wait_queue in an uninterruptible state.
I am not sure whether it really make any difference from any of the
freezer users point of view. (suspend, hotplug, kprobes etc ).
-aneesh
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