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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: . 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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