Re: [RFC][PATCH 4/7] Freezer: Fix vfork problem

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On 2/25/07, Pavel Machek <[email protected]> wrote:
Hi!

> Currently try_to_freeze_tasks() has to wait until all of the vforked processes
> exit and for this reason every user can make it fail.  To fix this problem
> we can introduce the additional process flag PF_FREEZER_SKIP to be used by tasks
> that do not want to be counted as freezable by the freezer and want to have
> TIF_FREEZE set nevertheless.  Then, this flag can be set by tasks using
> sys_vfork() before they call wait_for_completion() and cleared after they have
> woken up and called try_to_freeze().  In case such a task freezes with
> PF_FREEZER_SKIP set, refrigerator() clears this flag for the current task before
> calling frozen_process(current) to avoid having both PF_FREEZER_SKIP and
> PF_FROZEN set at the same time.
>
> Signed-off-by: Rafael J. Wysocki <[email protected]>

> @@ -1393,7 +1394,9 @@ long do_fork(unsigned long clone_flags,
>               tracehook_report_clone_complete(clone_flags, nr, p);
>
>               if (clone_flags & CLONE_VFORK) {
> +                     freezer_do_not_count();
>                       wait_for_completion(&vfork);
> +                     freezer_count();
>                       tracehook_report_vfork_done(p, nr);
>               }
>       } else {

All the infrastructure for this...Would it be easier to introduce

void fastcall __sched wait_for_completion_freezeable(struct completion *x)
{
        might_sleep();

        spin_lock_irq(&x->wait.lock);
        if (!x->done) {
                DECLARE_WAITQUEUE(wait, current);

                wait.flags |= WQ_FLAG_EXCLUSIVE;
                __add_wait_queue_tail(&x->wait, &wait);
                do {
                        __set_current_state(TASK_UNINTERRUPTIBLE);
                        spin_unlock_irq(&x->wait.lock);
                        schedule();
try_to_freeze(); /* HERE */
                        spin_lock_irq(&x->wait.lock);
                } while (!x->done);
                __remove_wait_queue(&x->wait, &wait);
        }
        x->done--;
        spin_unlock_irq(&x->wait.lock);
}



I don't see a call  to freezer_do_not_count here. Rafel was talking
about a similar change but that would involve special cases in
refrigerator such as  wakeup parent if the process which is going to
be frozen have vfork_done set.

if (->vfork_done) {
wakeup_parent()
}

how about

void fastcall __sched wait_for_completion_freezeable(struct completion *x)
{
    freezer_do_not_count();
    wait_for_completion(x);
    freezer_count();
}

-aneesh
-
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