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

Rafael J. Wysocki
2008-01-09T22:12:23Z

On Wednesday, 9 of January 2008, Alan Stern wrote:
> On Tue, 8 Jan 2008, Rafael J. Wysocki wrote:
>
> > Appended is what I managed to put together today.
> >
> > It probably still has some problems, but I'm not seeing them right now (too
> > tired). At least, it doesn't break my system. ;-)
> >
> > Please review.
>
> Okay, this seems to be better. I like the way the complicated tests
> are all localized in power/main.c.
>
> In dpm_resume() you shouldn't need to use dpm_list_mtx at all, because
> the list_move_tail() comes before the resume_device(). It's the same
> as in dpm_power_up().

Still, device_pm_schedule_removal() can (in theory) be called concurrently
with dpm_resume() by another thread and this might corrupt the list without
the locking.

> The same is true for dpm_suspend(). Once all the device have been
> locked, there shouldn't be any other tasks accessing the dpm lists.
> Hence there should be no need to protect the list.

Except for against theoretical races with device_pm_schedule_removal().

> Which reminds me, the kerneldoc for device_pm_schedule_removal() is
> inaccurate. The routine always just moves the device to dpm_destroy
> list for later processing.

Correct.

> Also, the kerneldoc for destroy_suspended_device() should contain an
> extra paragraph warning that the routine should never be called except
> within the scope of a system sleep transition. In practice this means
> it has to be directly or indirectly invoked by a suspend or resume
> method.

Or by a CPU hotplug notifier (that will be the majority of cases, IMO).

> It looks good.

Thanks for the review.

I'll fix the comments and repost the patch from scratch for merging in a
separate thread.

Greetings,
Rafael