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    SubjectRe: latest -git: hibernate: possible circular locking dependency detected
    On 08/21, Dmitry Adamushko wrote:
    >
    > however, I think there are 2 problems with handle_poweroff()
    > [ kernel/power/poweroff.c ]
    >
    > (1) it doesn't ensure that the 'cpu' it gets via
    > first_cpu(cpu_online_map) can't disappear (race with cpu_down()) on
    > the way to schedule_work_on()
    >
    > [ I pressume, neither generic sysrq nor console layer takes care of
    > it. They shoudn't of course ]
    >
    > (2) run_workqueue() [ which in the end calls do_poweroff() ] takes the
    > "cwq->lock" (which is lock-2 in our terminology)
    >
    > well, actually it release it before calling "work->fun()" but is the
    > 'lockdep' annotation right here? Peter?
    >
    > (I admit, I never looked at lockdep and do make assumptions on its syntax here).
    >
    > The lock-1 will be taken as a result of
    >
    > then, do_poweroff() -> kernel_power_off() -> disable_nonboot_cpus()
    >
    > which calls cpu_maps_update_begin() and takes "cpu_add_remove_lock"
    >
    > and this looks dangerous. Due to the same reason as was before with
    > the use of get_online_cpus() by workqueue handlers before
    > CPU_POST_DEAD introduction
    > (http://git.kernel.org/?p=linux/kernel/git/torvalds/linux-2.6.git;a=commit;h=3da1c84c00c7e5fa8348336bd8c342f9128b0f14)
    >
    > I guess, it may deadlock as the lock-1 has been already taken before
    > calling cleanup_workqueue_thread() -> flush_cpu_workqueue() and
    > completion of the former chain depends in turn on being able to
    > acquire the very same lock.

    I apologize in advance if I missed something else in your message,
    but I think you are very right. Please look at

    http://marc.info/?t=121580236300019

    Oleg.



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