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    SubjectRe: freezer problems
    On 02/21, Rafael J. Wysocki wrote:
    >
    > On Wednesday, 21 February 2007 19:14, Paul E. McKenney wrote:
    > > On Tue, Feb 20, 2007 at 07:29:01PM +0100, Rafael J. Wysocki wrote:
    > > > On Tuesday, 20 February 2007 01:32, Rafael J. Wysocki wrote:
    > > > > On Tuesday, 20 February 2007 01:12, Oleg Nesterov wrote:
    > > > > Hm. In the case discussed above we have a task that's right before calling
    > > > > frozen_process(), so we can't thaw it, because it's not frozen. It will be
    > > > > frozen just in a while, but try_to_freeze_tasks() and thaw_tasks() have no
    > > > > way to check this.
    > > > >
    > > > > I think to close this race the refrigerator should check TIF_FREEZE and set
    > > > > PF_FROZEN _and_ reset TIF_FREEZE under a lock

    I personally think this is good. Not only this allows us to close the race,
    I think we can do more.

    > that would also have to be
    > > > > taken by try_to_freeze_tasks() in the beginning of the error path. This will
    > > > > ensure that all tasks either freeze themselves before the error path in
    > > > > try_to_freeze_tasks() is executed, or remain unfrozen.

    How about take this lock in thaw_tasks() instead/too ?

    Currently we need a separate loop in thaw_tasks() to handle PF_FREEZER_SKIP. This
    means that PF_FREEZER_SKIP is not so generic: thaw_tasks() can't tolerate if such
    a task was woken in between. What if we change thaw_process() to clear TIF_FREEZE ?

    Note also that we can use task_lock() instead of global refrigerator_lock. This
    means that thaw_process() should take it too, probably this is slowdown, but I
    think not too much because thaw_process() is going to write to p->flags anyway.
    In this case thaw_process() works perfectly as cancel_freezing_and_thaw() and
    can be used to fix exec/coredump in future.

    Thoughts?

    Oleg.

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