linux-kernel - Re: [PATCH] PM: Prevent waiting forever on asynchronous resume after abort

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Message-ID: <Pine.LNX.4.44L0.1009020946580.1513-100000@iolanthe.rowland.org>
Date:	Thu, 2 Sep 2010 09:50:14 -0400 (EDT)
From:	Alan Stern <stern@...land.harvard.edu>
To:	Colin Cross <ccross@...roid.com>
cc:	linux-kernel@...r.kernel.org,
	<linux-pm@...ts.linux-foundation.org>, Pavel Machek <pavel@....cz>,
	"Rafael J. Wysocki" <rjw@...k.pl>, Len Brown <len.brown@...el.com>,
	Greg Kroah-Hartman <gregkh@...e.de>,
	Randy Dunlap <randy.dunlap@...cle.com>,
	Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: [PATCH] PM: Prevent waiting forever on asynchronous resume after
 abort

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@...roid.com>
> ---
>  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().

Alan Stern

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