linux-kernel - Re: [RFC][PATCH] PM: Make PM core handle device registrations concurrent with suspend/hibernation

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Message-ID: <Pine.LNX.4.44L0.0803041041270.4039-100000@iolanthe.rowland.org>
Date:	Tue, 4 Mar 2008 11:01:14 -0500 (EST)
From:	Alan Stern <stern@...land.harvard.edu>
To:	"Rafael J. Wysocki" <rjw@...k.pl>
cc:	pm list <linux-pm@...ts.linux-foundation.org>,
	Alexey Starikovskiy <astarikovskiy@...e.de>,
	Pavel Machek <pavel@....cz>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: [RFC][PATCH] PM: Make PM core handle device registrations
 concurrent with suspend/hibernation

On Tue, 4 Mar 2008, Rafael J. Wysocki wrote:

> Hi,
> 
> The appended patch is intended to fix the issue with the PM core that it allows
> device registrations to complete successfully even if they run concurrently
> with the suspending of their parents, which may lead to a wrong ordering of
> devices on the dpm_active list and, as a result, to failures during suspend and
> hibernation transitions.
> 
> Comments welcome.

> Index: linux-2.6/include/linux/pm.h
> ===================================================================
> --- linux-2.6.orig/include/linux/pm.h
> +++ linux-2.6/include/linux/pm.h
> @@ -186,6 +186,7 @@ struct dev_pm_info {
>  #ifdef	CONFIG_PM_SLEEP
>  	unsigned		should_wakeup:1;
>  	struct list_head	entry;
> +	bool			sleeping;	/* Owned by the PM core */
>  #endif
>  };

Drivers might want to use this field without having to add protective 
"#ifdef CONFIG_PM_SLEEP" lines.  You can change it to a single-bit 
bitfield and place it adjacent to can_wakeup.

> -void device_pm_add(struct device *dev)
> +int device_pm_add(struct device *dev)
>  {
> +	int error = 0;
> +
>  	pr_debug("PM: Adding info for %s:%s\n",
>  		 dev->bus ? dev->bus->name : "No Bus",
>  		 kobject_name(&dev->kobj));
>  	mutex_lock(&dpm_list_mtx);
> -	list_add_tail(&dev->power.entry, &dpm_active);
> +	if (dev->parent && dev->parent->power.sleeping)
> +		error = -EBUSY;

Add a stack dump?  When this isn't a race, it's the kind of bug we want
to fix.

> +	else
> +		list_add_tail(&dev->power.entry, &dpm_active);
>  	mutex_unlock(&dpm_list_mtx);
> +	return error;
>  }

> @@ -426,6 +404,11 @@ static int dpm_suspend(pm_message_t stat
>  		struct list_head *entry = dpm_active.prev;
>  		struct device *dev = to_device(entry);
>  
> +		if (dev->parent && dev->parent->power.sleeping) {
> +			error = -EAGAIN;
> +			break;
> +		}

It's not clear that we want to have this check.  It would cause
problems if the device ordering got mixed up by device_move(), which is
pretty much the only way it could be triggered.

If you do want to leave it in, add a stack dump (and perhaps make it 
not return an error).  This would help force people to figure out safe 
ways to use device_move().

> +		dev->power.sleeping = true;;

Extra ';'.

Alan Stern

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