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SubjectRe: [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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