linux-kernel - Re: [PATCH 2/3] power: increment wakeup_count when save_wakeup

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Date:	Mon, 18 May 2015 02:47:01 +0200
From:	"Rafael J. Wysocki" <rjw@...ysocki.net>
To:	Jin Qian <jinqian@...roid.com>
Cc:	Len Brown <len.brown@...el.com>, Pavel Machek <pavel@....cz>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	linux-pm@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 2/3] power: increment wakeup_count when save_wakeup_count failed.

On Friday, May 15, 2015 06:08:32 PM Jin Qian wrote:
> Some wakeup event happens every frequently between reading
> wakeup_count and writing back wakeup_count.
> They changed wakeup event count so writes fail and usespace doesn't
> continue to suspend. However, such
> occurrences are not counted in ws->wakeup_count.

So I hope you've read the comment in wakeup_source_report_event().

> I spent quite sometime finding out the problematic wakeup
> event with inaccurate wakeup_count : )

But your patch doesn't fix the problem.  ws->wakeup_count is still racy
and kind of even more after the patch than before.


> On Fri, May 15, 2015 at 5:34 PM, Rafael J. Wysocki <rjw@...ysocki.net> wrote:
> > On Wednesday, April 22, 2015 05:50:11 PM Jin Qian wrote:
> >> user-space aborts suspend attempt if writing wakeup_count failed.
> >> Count the write failure towards wakeup_count.
> >
> > A use case, please?
> >
> >> Signed-off-by: Jin Qian <jinqian@...roid.com>
> >> ---
> >>  drivers/base/power/wakeup.c | 17 +++++++++++++++++
> >>  1 file changed, 17 insertions(+)
> >>
> >> diff --git a/drivers/base/power/wakeup.c b/drivers/base/power/wakeup.c
> >> index f24c622..bdb45f3 100644
> >> --- a/drivers/base/power/wakeup.c
> >> +++ b/drivers/base/power/wakeup.c
> >> @@ -57,6 +57,8 @@ static LIST_HEAD(wakeup_sources);
> >>
> >>  static DECLARE_WAIT_QUEUE_HEAD(wakeup_count_wait_queue);
> >>
> >> +static ktime_t last_read_time;
> >> +
> >>  /**
> >>   * wakeup_source_prepare - Prepare a new wakeup source for initialization.
> >>   * @ws: Wakeup source to prepare.
> >> @@ -771,10 +773,15 @@ void pm_wakeup_clear(void)
> >>  bool pm_get_wakeup_count(unsigned int *count, bool block)
> >>  {
> >>       unsigned int cnt, inpr;
> >> +     unsigned long flags;
> >>
> >>       if (block) {
> >>               DEFINE_WAIT(wait);
> >>
> >> +             spin_lock_irqsave(&events_lock, flags);
> >> +             last_read_time = ktime_get();
> >> +             spin_unlock_irqrestore(&events_lock, flags);
> >> +
> >>               for (;;) {
> >>                       prepare_to_wait(&wakeup_count_wait_queue, &wait,
> >>                                       TASK_INTERRUPTIBLE);
> >> @@ -806,6 +813,7 @@ bool pm_save_wakeup_count(unsigned int count)
> >>  {
> >>       unsigned int cnt, inpr;
> >>       unsigned long flags;
> >> +     struct wakeup_source *ws;
> >>
> >>       events_check_enabled = false;
> >>       spin_lock_irqsave(&events_lock, flags);
> >> @@ -813,6 +821,15 @@ bool pm_save_wakeup_count(unsigned int count)
> >>       if (cnt == count && inpr == 0) {
> >>               saved_count = count;
> >>               events_check_enabled = true;
> >> +     } else {
> >> +             rcu_read_lock();
> >> +             list_for_each_entry_rcu(ws, &wakeup_sources, entry) {
> >> +                     if (ws->active ||
> >> +                         ktime_compare(ws->last_time, last_read_time) > 0) {
> >> +                             ws->wakeup_count++;
> >> +                     }
> >> +             }
> >> +             rcu_read_unlock();
> >>       }
> >>       spin_unlock_irqrestore(&events_lock, flags);
> >>       return events_check_enabled;
> >>
> >
> > --
> > I speak only for myself.
> > Rafael J. Wysocki, Intel Open Source Technology Center.
> --
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-- 
I speak only for myself.
Rafael J. Wysocki, Intel Open Source Technology Center.
--
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