On Thursday, September 02, 2010, Colin Cross wrote: > On Thu, Sep 2, 2010 at 12:46 PM, Rafael J. Wysocki <rjw@xxxxxxx> wrote: > > On Thursday, September 02, 2010, Alan Stern wrote: > >> On Wed, 1 Sep 2010, Colin Cross wrote: > >> > >> > Only wait on a parent device during resume if the parent device is > >> > suspended. > >> > > >> > Consider three drivers, A, B, and C. The parent of A is C, and C > >> > has async_suspend set. On boot, C->power.completion is initialized > >> > to 0. > >> > > >> > During the first suspend: > >> > suspend_devices_and_enter(...) > >> > dpm_resume(...) > >> > device_suspend(A) > >> > device_suspend(B) returns error, aborts suspend > >> > dpm_resume_end(...) > >> > dpm_resume(...) > >> > device_resume(A) > >> > dpm_wait(A->parent == C) > >> > wait_for_completion(C->power.completion) > >> > > >> > The wait_for_completion will never complete, because > >> > complete_all(C->power.completion) will only be called from > >> > device_suspend(C) or device_resume(C), neither of which is called > >> > if suspend is aborted before C. > >> > >> This would work okay if C->power.completion had been initialized to the > >> completed state during boot, right? > >> > >> > After a successful suspend->resume cycle, where B doesn't abort > >> > suspend, C->power.completion is left in the completed state by the > >> > call to device_resume(C), and the same call path will work if B > >> > aborts suspend. > >> > > >> > Signed-off-by: Colin Cross <ccross@xxxxxxxxxxx> > >> > --- > >> > drivers/base/power/main.c | 3 ++- > >> > 1 files changed, 2 insertions(+), 1 deletions(-) > >> > > >> > diff --git a/drivers/base/power/main.c b/drivers/base/power/main.c > >> > index cb784a0..e159910 100644 > >> > --- a/drivers/base/power/main.c > >> > +++ b/drivers/base/power/main.c > >> > @@ -526,7 +526,8 @@ static int device_resume(struct device *dev, pm_message_t state, bool async) > >> > TRACE_DEVICE(dev); > >> > TRACE_RESUME(0); > >> > > >> > - dpm_wait(dev->parent, async); > >> > + if (dev->parent && dev->parent->power.status >= DPM_OFF) > >> > + dpm_wait(dev->parent, async); > >> > device_lock(dev); > >> > > >> > dev->power.status = DPM_RESUMING; > >> > >> I think it would be better to change device_pm_init() and add a > >> complete_all(). > > > > I agree. > That would work, and was my first solution, but it increases the > reliance on the completion variable being left completed between state > transitions, which is undocumented and unnecessary. In fact it is necessary, because dpm_wait() may be called by external code through device_pm_wait_for_dev() which is exported for a reason. That may lead to problems analogous to the one you described if the completion variables are not completed initially. > It seems more straightforward to me to only wait on the parent if the parent is > suspended. > > > Who's writing the patch? > I'll write it if you still don't like this one. Yes, please. Thanks, Rafael _______________________________________________ linux-pm mailing list linux-pm@xxxxxxxxxxxxxxxxxxxxxxxxxx https://lists.linux-foundation.org/mailman/listinfo/linux-pm
