linux-kernel - Re: [PATCH 2/2] PM / sleep: don't suspend parent when async child suspend

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Date:   Wed, 19 Oct 2016 17:56:28 -0700
From:   Dmitry Torokhov <dmitry.torokhov@...il.com>
To:     Brian Norris <briannorris@...omium.org>
Cc:     "Rafael J . Wysocki" <rjw@...ysocki.net>,
        Pavel Machek <pavel@....cz>, Len Brown <len.brown@...el.com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        linux-kernel@...r.kernel.org,
        Doug Anderson <dianders@...omium.org>,
        Brian Norris <computersforpeace@...il.com>,
        Jeffy Chen <jeffy.chen@...k-chips.com>,
        linux-pm@...r.kernel.org, Chuansheng Liu <chuansheng.liu@...el.com>
Subject: Re: [PATCH 2/2] PM / sleep: don't suspend parent when async child
 suspend_{noirq,early} fails

On Wed, Oct 19, 2016 at 05:26:10PM -0700, Brian Norris wrote:
> Consider two devices, A and B, where B is a child of A, and B utilizes
> asynchronous suspend (it does not matter whether A is sync or async). If
> B fails to suspend_noirq() or suspend_early(), or is interrupted by a
> wakeup (pm_wakeup_pending()), then it aborts and sets the async_error
> variable. However, device A does not (immediately) check the async_error
> variable; it may continue to run its own suspend_noirq()/suspend_early()
> callback. This is bad.
> 
> We can resolve this problem by checking the async_error flag after
> waiting for children to suspend, using the same logic for the noirq and
> late suspend cases as we already do for __device_suspend().
> 
> It's easy to observe this erroneous behavior by, for example, forcing a
> device to sleep a bit in its suspend_noirq() (to ensure the parent is
> waiting for the child to complete), then return an error, and watch the
> parent suspend_noirq() still get called. (Or similarly, fake a wakeup
> event at the right (or is it wrong?) time.)
> 
> Fixes: de377b397272 ("PM / sleep: Asynchronous threads for suspend_late")
> Fixes: 28b6fd6e3779 ("PM / sleep: Asynchronous threads for suspend_noirq")
> Reported-by: Jeffy Chen <jeffy.chen@...k-chips.com>
> Signed-off-by: Brian Norris <briannorris@...omium.org>

Makes sense to me.

Reviewed-by: Dmitry Torokhov <dmitry.torokhov@...il.com>

> ---
> Tested mostly on 4.4, but the code (and seemingly the bug) is mostly untouched
> since then. I can try to conjure up a proper upstream test if required.
> 
>  drivers/base/power/main.c | 6 ++++++
>  1 file changed, 6 insertions(+)
> 
> diff --git a/drivers/base/power/main.c b/drivers/base/power/main.c
> index c58563581345..eaf6b53463a5 100644
> --- a/drivers/base/power/main.c
> +++ b/drivers/base/power/main.c
> @@ -1040,6 +1040,9 @@ static int __device_suspend_noirq(struct device *dev, pm_message_t state, bool a
>  
>  	dpm_wait_for_children(dev, async);
>  
> +	if (async_error)
> +		goto Complete;
> +
>  	if (dev->pm_domain) {
>  		info = "noirq power domain ";
>  		callback = pm_noirq_op(&dev->pm_domain->ops, state);
> @@ -1187,6 +1190,9 @@ static int __device_suspend_late(struct device *dev, pm_message_t state, bool as
>  
>  	dpm_wait_for_children(dev, async);
>  
> +	if (async_error)
> +		goto Complete;
> +
>  	if (dev->pm_domain) {
>  		info = "late power domain ";
>  		callback = pm_late_early_op(&dev->pm_domain->ops, state);
> -- 
> 2.8.0.rc3.226.g39d4020
> 

-- 
Dmitry