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    SubjectRe: [PATCH] PM: Acquire device locks on suspend
    On Mon, 7 Jan 2008, Rafael J. Wysocki wrote:

    > Please see the patch at: http://lkml.org/lkml/2008/1/6/298 . It represents my
    > current idea about how to do that.

    It has some problems.

    First, note that the list manipulations in dpm_suspend(),
    device_power_down(), and so on aren't protected by dpm_list_mtx. So
    your patch could corrupt the list pointers. Are you assuming that no
    other threads can be running at this time?

    Note also that device_pm_destroy_suspended() does up(&dev->sem), but it
    doesn't know whether or not dev->sem was locked to begin with.

    Do you want to rule out the possibility of a driver's suspend or remove
    methods calling destroy_suspended_device() on its own device? With
    your synchronous approach, this would mean that the suspend/resume
    method would indirectly end up calling the remove method. This is
    dangerous at best; with USB it would be a lockdep violation. With an
    asynchronous approach, on the other hand, this wouldn't be a problem.

    Alan Stern



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