linux-kernel - Re: [PATCH] PM / s2idle: Clear the events_check

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Date:   Mon, 6 Nov 2017 12:13:26 +0100
From:   Pavel Machek <pavel@....cz>
To:     Rajat Jain <rajatja@...gle.com>
Cc:     "Rafael J. Wysocki" <rjw@...ysocki.net>,
        Len Brown <len.brown@...el.com>, linux-pm@...r.kernel.org,
        linux-kernel@...r.kernel.org, dtor@...gle.com, rajatxjain@...il.com
Subject: Re: [PATCH] PM / s2idle: Clear the events_check_enabled flag

On Tue 2017-10-31 14:44:24, Rajat Jain wrote:
> Problem: This flag does not get cleared currently in the suspend or
> resume path in the following cases:
> 
> * In case some driver's suspend routine returns an error.
> * Successful s2idle case
> * etc?
> 
> Why is this a problem: What happens is that the next suspend attempt
> could fail even though the user did not enable the flag by writing to
> /sys/power/wakeup_count. This is 1 use case how the issue can be seen
> (but similar use case with driver suspend failure can be thought of):
> 
> 1. Read /sys/power/wakeup_count
> 2. echo count > /sys/power/wakeup_count
> 3. echo freeze > /sys/power/wakeup_count
> 4. Let the system suspend, and wakeup the system using some wake source
>    that calls pm_wakeup_event() e.g. power button or something.
> 5. Note that the combined wakeup count would be incremented due
>    to the pm_wakeup_event() in the resume path.
> 6. After resuming the events_check_enabled flag is still set.
> 
> At this point if the user attempts to freeze again (without writing to
> /sys/power/wakeup_count), the suspend would fail even though there has
> been no wake event since the past resume.
> 
> What this patch does:
> 
> It moves the clearing of the flag to just before a resume is completed,
> so that it is always cleared for the corner cases mentioned above.
> 
> Signed-off-by: Rajat Jain <rajatja@...gle.com>

Acked-by: Pavel Machek <pavel@....cz>
-- 
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(cesky, pictures) http://atrey.karlin.mff.cuni.cz/~pavel/picture/horses/blog.html

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