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    SubjectRe: [RC][PATCH -mm] PM: Prevent frozen user mode helpers from failing the freezing of tasks
    Hi!

    > From: Rafael J. Wysocki <rjw@sisk.pl>
    >
    > At present, if a user mode helper is running while usermodehelper_pm_callback()
    > is executed, the helper may be frozen and the completion in
    > call_usermodehelper_exec() won't be completed until user space processes are
    > thawed. As a result, the freezing of kernel threads may fail, which is not
    > desirable.
    >
    > Prevent this from happening by introducing a counter of running user mode
    > helpers and allowing usermodehelper_pm_callback() to succeed for
    > action = PM_HIBERNATION_PREPARE or action = PM_SUSPEND_PREPARE only if there
    > are no helpers running. [Namely, usermodehelper_pm_callback() waits for at most
    > RUNNING_HELPERS_TIMEOUT for the number of running helpers to become zero and
    > fails if that doesn't happen.]
    >
    > Special thanks to Uli Luckas <u.luckas@road.de> for reviewing the previous
    > versions of this patch and for very useful comments.
    ...
    > Reviewed-by: Pavel Machek <pavel@ucw.cz>

    Eh, not sure this header is worth anything. Sometimes I'm lazy and
    stop when I see first problem.

    > switch (action) {
    > case PM_HIBERNATION_PREPARE:
    > case PM_SUSPEND_PREPARE:
    > usermodehelper_disabled = 1;
    > - return NOTIFY_OK;
    > + retval = wait_event_timeout(running_helpers_waitq,
    > + atomic_read(&running_helpers) == 0,

    Are you sure here? What happens when atomic variable changes between
    the atomic_read and the function call?
    Pavel
    --
    (english) http://www.livejournal.com/~pavelmachek
    (cesky, pictures) http://atrey.karlin.mff.cuni.cz/~pavel/picture/horses/blog.html
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