Re: [PATCH] PM: Acquire device locks on suspend

[Alan Stern]

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

--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/