On 02/18, Rafael J. Wysocki wrote:
>
> > On Sunday, 18 February 2007 12:31, Oleg Nesterov wrote:
> > >
> > > A very vague idea: what if parent will do
> > >
> > > current->flags |= PF_PLEASE_CONSIDER_ME_AS_FROZEN_BUT_SET_TIF_FREEZE
> > > wait_for_completion(&vfork);
> > > try_to_freeze();
> > >
> > > ?
>
> Hm, what about the following patch instead?
>
> The problem is that if the child enters the refrigeratior, we can't freeze the
> parent, because it's uninterruptible, but the child knows the parent will be
> uninterruptible until it exits, so the child can mark the parent as frozen.
>
> --- linux-2.6.20-mm2.orig/kernel/power/process.c 2007-02-18 15:43:30.000000000 +0100
> +++ linux-2.6.20-mm2/kernel/power/process.c 2007-02-18 16:09:53.000000000 +0100
> @@ -39,6 +39,13 @@ void refrigerator(void)
> /* Hmm, should we be allowed to suspend when there are realtime
> processes around? */
> long save;
> +
> + /* The parent is uninterruptible and will stay so until this task exits,
> + * so we can mark it as frozen.
> + */
> + if (current->vfork_done)
> + frozen_process(current->parent);
This is not safe. task->flags is not atomic, we can change ->flags only
if we know the task won't touch it itself (ptrace, thaw_process).
The parent could be interrupted, irq may play with current->flags (slab,
for example).
Please note that ->parent may do things like ptrace_notify() before
it actually sleeps on ->vfork_done. This means that even if we could
set PF_FROZEN in a safe manner, this doesn't look like a good idea.
> +
> + if (current->vfork_done && frozen(current->parent))
> + current->parent->flags &= ~PF_FROZEN;
> }
Why? If the code above works, we shouldn't take care about frozen
->parent?
Oleg.
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