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    SubjectRe: [PATCH 10/16] freezer: fix set_freezable[_with_signal]() race
    On 08/19, Tejun Heo wrote:
    >
    > A kthread doing set_freezable*() may race with on-going PM freeze and
    > the freezer might think all tasks are frozen while the new freezable
    > kthread is marrily proceeding to execute code paths which aren't
    > supposed to be executing during PM freeze.

    Yes,

    > +bool __set_freezable(bool with_signal)
    > +{
    > + might_sleep();
    > +
    > + /*
    > + * Modify flags while holding freezer_lock. This ensures the
    > + * freezer notices that we aren't frozen yet or the freezing
    > + * condition is visible to try_to_freeze() below.
    > + */
    > + spin_lock_irq(&freezer_lock);
    > + current->flags &= ~PF_NOFREEZE;
    > + if (with_signal)
    > + current->flags &= ~PF_FREEZER_NOSIG;
    > + spin_unlock_irq(&freezer_lock);
    > +
    > + return try_to_freeze();
    > +}

    You know, I was really, really puzzled by this change. Because it
    "obviously can fix nothing", and try_to_freeze() makes no sense
    (ignoring the very unlikely case when TIF_FREEZING was set right
    after we drop freezer_lock).

    But I guess this works along with 14/16 which removes TIF_FREEZING.

    Oleg.



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