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Date: Sat, 19 Jun 2010 22:52:54 -0700
From: mark gross <640e9920@...il.com>
To: "Rafael J. Wysocki" <rjw@...k.pl>
Cc: linux-pm@...ts.linux-foundation.org,
Alan Stern <stern@...land.harvard.edu>,
Matthew Garrett <mjg59@...f.ucam.org>,
Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
Dmitry Torokhov <dmitry.torokhov@...il.com>,
Arve Hjønnevåg <arve@...roid.com>,
Neil Brown <neilb@...e.de>, mark gross <640e9920@...il.com>
Subject: Re: [RFC][PATCH] PM: Avoid losing wakeup events during suspend
On Sun, Jun 20, 2010 at 12:05:35AM +0200, Rafael J. Wysocki wrote:
> Hi,
>
> One of the arguments during the suspend blockers discussion was that the
> mainline kernel didn't contain any mechanisms allowing it to avoid losing
> wakeup events during system suspend.
>
> Generally, there are two problems in that area. First, if a wakeup event
> occurs exactly at the same time when /sys/power/state is being written to,
> the even may be delivered to user space right before the freezing of it,
> in which case the user space consumer of the event may not be able to process
yes this is racy. souldn't the wakeup event handers/driver force a user
mode ACK before they stop failing suspend attempts?
> it before the system is suspended. Second, if a wakeup event occurs after user
> space has been frozen and that event is not a wakeup interrupt, the kernel will
> not react to it and the system will be suspended.
If its not a wakeup interrupt is it not fair to allow the suspend to
happen even if its handler's are "in flight" at suspend time?
>
> The following patch illustrates my idea of how these two problems may be
> addressed. It introduces a new global sysfs attribute,
> /sys/power/wakeup_count, associated with a running counter of wakeup events
> and a helper function, pm_wakeup_event(), that may be used by kernel subsystems
> to increment the wakeup events counter.
>
> /sys/power/wakeup_count may be read from or written to by user space. Reads
> will always succeed and return the current value of the wakeup events counter.
> Writes, however, will only succeed if the written number is equal to the
> current value of the wakeup events counter. If a write is successful, it will
> cause the kernel to save the current value of the wakeup events counter and
> to compare the saved number with the current value of the counter at certain
> points of the subsequent suspend (or hibernate) sequence. If the two values
> don't match, the suspend will be aborted just as though a wakeup interrupt
> happened. Reading from /sys/power/wakeup_count again will turn that mechanism
> off.
why would you want to turn it off?
>
> The assumption is that there's a user space power manager that will first
> read from /sys/power/wakeup_count. Then it will check all user space consumers
> of wakeup events known to it for unprocessed events. If there are any, it will
> wait for them to be processed and repeat. In turn, if there are not any,
> it will try to write to /sys/power/wakeup_count and if the write is successful,
> it will write to /sys/power/state to start suspend, so if any wakeup events
> accur past that point, they will be noticed by the kernel and will eventually
> cause the suspend to be aborted.
>
> In addition to the above, the patch adds a wakeup events counter to the
> power member of struct device and makes these per-device wakeup event counters
> available via sysfs, so that it's possible to check the activity of various
> wakeup event sources within the kernel.
>
> To illustrate how subsystems can use pm_wakeup_event(), I added it to the
> PCI runtime PM wakeup-handling code.
>
> At the moment the patch only contains code changes (ie. no documentation),
> but I'm going to add comments etc. if people like the idea.
>
> Please tell me what you think.
>
> Rafael
>
> ---
> drivers/base/power/Makefile | 2 -
> drivers/base/power/main.c | 1
> drivers/base/power/power.h | 3 +
> drivers/base/power/sysfs.c | 9 ++++
> drivers/base/power/wakeup.c | 74 ++++++++++++++++++++++++++++++++++++++++
> drivers/pci/pci-acpi.c | 2 +
> drivers/pci/pcie/pme/pcie_pme.c | 2 +
> include/linux/pm.h | 6 +++
> kernel/power/hibernate.c | 14 ++++---
> kernel/power/main.c | 24 ++++++++++++
> kernel/power/power.h | 6 +++
> kernel/power/suspend.c | 2 -
> 12 files changed, 138 insertions(+), 7 deletions(-)
>
> Index: linux-2.6/kernel/power/main.c
> ===================================================================
> --- linux-2.6.orig/kernel/power/main.c
> +++ linux-2.6/kernel/power/main.c
> @@ -204,6 +204,28 @@ static ssize_t state_store(struct kobjec
>
> power_attr(state);
>
> +static ssize_t wakeup_count_show(struct kobject *kobj,
> + struct kobj_attribute *attr,
> + char *buf)
> +{
> + return sprintf(buf, "%lu\n", pm_get_wakeup_count());
> +}
> +
> +static ssize_t wakeup_count_store(struct kobject *kobj,
> + struct kobj_attribute *attr,
> + const char *buf, size_t n)
> +{
> + unsigned long val;
> +
> + if (sscanf(buf, "%lu", &val) == 1) {
> + if (pm_save_wakeup_count(val))
> + return n;
> + }
> + return -EINVAL;
> +}
> +
> +power_attr(wakeup_count);
> +
> #ifdef CONFIG_PM_TRACE
> int pm_trace_enabled;
>
> @@ -236,6 +258,7 @@ static struct attribute * g[] = {
> #endif
> #ifdef CONFIG_PM_SLEEP
> &pm_async_attr.attr,
> + &wakeup_count_attr.attr,
> #ifdef CONFIG_PM_DEBUG
> &pm_test_attr.attr,
> #endif
> @@ -266,6 +289,7 @@ static int __init pm_init(void)
> int error = pm_start_workqueue();
> if (error)
> return error;
> + pm_wakeup_events_init();
> power_kobj = kobject_create_and_add("power", NULL);
> if (!power_kobj)
> return -ENOMEM;
> Index: linux-2.6/drivers/base/power/wakeup.c
> ===================================================================
> --- /dev/null
> +++ linux-2.6/drivers/base/power/wakeup.c
> @@ -0,0 +1,74 @@
> +
> +#include <linux/device.h>
> +#include <linux/pm.h>
> +
> +static unsigned long event_count;
> +static unsigned long saved_event_count;
what about over flow issues?
> +static bool events_check_enabled;
> +static spinlock_t events_lock;
> +
> +void pm_wakeup_events_init(void)
> +{
> + spin_lock_init(&events_lock);
> +}
> +
> +void pm_wakeup_event(struct device *dev)
> +{
> + unsigned long flags;
> +
> + spin_lock_irqsave(&events_lock, flags);
> + event_count++;
should event_count be an atomic type so we can not bother with taking
the evnets_lock?
> + if (dev)
> + dev->power.wakeup_count++;
> + spin_unlock_irqrestore(&events_lock, flags);
> +}
> +
> +bool pm_check_wakeup_events(bool enable)
> +{
> + unsigned long flags;
> + bool ret;
> +
> + spin_lock_irqsave(&events_lock, flags);
> + ret = !events_check_enabled || (event_count == saved_event_count);
I'm not getting the events_check_enbled flag yet.
> + events_check_enabled = enable;
I'm not sure if this is the right thing depending on all the different
ways the boolians are interacting with eachother.
Which is a red flag to me. This code is confusing.
I'll look at it some more when I'm fresh tomorrow.
--mgross
> + spin_unlock_irqrestore(&events_lock, flags);
> + return ret;
> +}
> +
> +unsigned long pm_get_wakeup_count(void)
> +{
> + unsigned long flags;
> + unsigned long count;
> +
> + spin_lock_irqsave(&events_lock, flags);
> + events_check_enabled = false;
> + count = event_count;
> + spin_unlock_irqrestore(&events_lock, flags);
> + return count;
> +}
> +
> +bool pm_save_wakeup_count(unsigned long count)
> +{
> + unsigned long flags;
> + bool ret = false;
> +
> + spin_lock_irqsave(&events_lock, flags);
> + if (count == event_count) {
> + saved_event_count = count;
> + events_check_enabled = true;
> + ret = true;
> + }
> + spin_unlock_irqrestore(&events_lock, flags);
> + return ret;
> +}
> +
> +unsigned long pm_dev_wakeup_count(struct device *dev)
> +{
> + unsigned long flags;
> + unsigned long count;
> +
> + spin_lock_irqsave(&events_lock, flags);
> + count = dev->power.wakeup_count;
> + spin_unlock_irqrestore(&events_lock, flags);
> + return count;
> +}
> Index: linux-2.6/include/linux/pm.h
> ===================================================================
> --- linux-2.6.orig/include/linux/pm.h
> +++ linux-2.6/include/linux/pm.h
> @@ -457,6 +457,7 @@ struct dev_pm_info {
> #ifdef CONFIG_PM_SLEEP
> struct list_head entry;
> struct completion completion;
> + unsigned long wakeup_count;
> #endif
> #ifdef CONFIG_PM_RUNTIME
> struct timer_list suspend_timer;
> @@ -552,6 +553,9 @@ extern void __suspend_report_result(cons
> } while (0)
>
> extern void device_pm_wait_for_dev(struct device *sub, struct device *dev);
> +
> +/* drivers/base/power/wakeup.c */
> +extern void pm_wakeup_event(struct device *dev);
> #else /* !CONFIG_PM_SLEEP */
>
> #define device_pm_lock() do {} while (0)
> @@ -565,6 +569,8 @@ static inline int dpm_suspend_start(pm_m
> #define suspend_report_result(fn, ret) do {} while (0)
>
> static inline void device_pm_wait_for_dev(struct device *a, struct device *b) {}
> +
> +static inline void pm_wakeup_event(struct device *dev) {}
> #endif /* !CONFIG_PM_SLEEP */
>
> /* How to reorder dpm_list after device_move() */
> Index: linux-2.6/drivers/base/power/Makefile
> ===================================================================
> --- linux-2.6.orig/drivers/base/power/Makefile
> +++ linux-2.6/drivers/base/power/Makefile
> @@ -1,5 +1,5 @@
> obj-$(CONFIG_PM) += sysfs.o
> -obj-$(CONFIG_PM_SLEEP) += main.o
> +obj-$(CONFIG_PM_SLEEP) += main.o wakeup.o
> obj-$(CONFIG_PM_RUNTIME) += runtime.o
> obj-$(CONFIG_PM_OPS) += generic_ops.o
> obj-$(CONFIG_PM_TRACE_RTC) += trace.o
> Index: linux-2.6/drivers/base/power/main.c
> ===================================================================
> --- linux-2.6.orig/drivers/base/power/main.c
> +++ linux-2.6/drivers/base/power/main.c
> @@ -59,6 +59,7 @@ void device_pm_init(struct device *dev)
> {
> dev->power.status = DPM_ON;
> init_completion(&dev->power.completion);
> + dev->power.wakeup_count = 0;
> pm_runtime_init(dev);
> }
>
> Index: linux-2.6/kernel/power/power.h
> ===================================================================
> --- linux-2.6.orig/kernel/power/power.h
> +++ linux-2.6/kernel/power/power.h
> @@ -184,6 +184,12 @@ static inline void suspend_test_finish(c
> #ifdef CONFIG_PM_SLEEP
> /* kernel/power/main.c */
> extern int pm_notifier_call_chain(unsigned long val);
> +
> +/* drivers/base/power/wakeup.c */
> +extern void pm_wakeup_events_init(void);
> +extern bool pm_check_wakeup_events(bool enable);
> +extern unsigned long pm_get_wakeup_count(void);
> +extern bool pm_save_wakeup_count(unsigned long count);
> #endif
>
> #ifdef CONFIG_HIGHMEM
> Index: linux-2.6/kernel/power/suspend.c
> ===================================================================
> --- linux-2.6.orig/kernel/power/suspend.c
> +++ linux-2.6/kernel/power/suspend.c
> @@ -157,7 +157,7 @@ static int suspend_enter(suspend_state_t
>
> error = sysdev_suspend(PMSG_SUSPEND);
> if (!error) {
> - if (!suspend_test(TEST_CORE))
> + if (!suspend_test(TEST_CORE) && pm_check_wakeup_events(false))
> error = suspend_ops->enter(state);
> sysdev_resume();
> }
> Index: linux-2.6/kernel/power/hibernate.c
> ===================================================================
> --- linux-2.6.orig/kernel/power/hibernate.c
> +++ linux-2.6/kernel/power/hibernate.c
> @@ -277,7 +277,7 @@ static int create_image(int platform_mod
> goto Enable_irqs;
> }
>
> - if (hibernation_test(TEST_CORE))
> + if (hibernation_test(TEST_CORE) || !pm_check_wakeup_events(true))
> goto Power_up;
>
> in_suspend = 1;
> @@ -511,14 +511,18 @@ int hibernation_platform_enter(void)
>
> local_irq_disable();
> sysdev_suspend(PMSG_HIBERNATE);
> + if (!pm_check_wakeup_events(false))
> + goto Power_up;
> +
> hibernation_ops->enter();
> /* We should never get here */
> while (1);
>
> - /*
> - * We don't need to reenable the nonboot CPUs or resume consoles, since
> - * the system is going to be halted anyway.
> - */
> + Power_up:
> + sysdev_resume();
> + local_irq_enable();
> + enable_nonboot_cpus();
> +
> Platform_finish:
> hibernation_ops->finish();
>
> Index: linux-2.6/drivers/pci/pci-acpi.c
> ===================================================================
> --- linux-2.6.orig/drivers/pci/pci-acpi.c
> +++ linux-2.6/drivers/pci/pci-acpi.c
> @@ -48,6 +48,8 @@ static void pci_acpi_wake_dev(acpi_handl
> if (event == ACPI_NOTIFY_DEVICE_WAKE && pci_dev) {
> pci_check_pme_status(pci_dev);
> pm_runtime_resume(&pci_dev->dev);
> + if (device_may_wakeup(&pci_dev->dev))
> + pm_wakeup_event(&pci_dev->dev);
> if (pci_dev->subordinate)
> pci_pme_wakeup_bus(pci_dev->subordinate);
> }
> Index: linux-2.6/drivers/pci/pcie/pme/pcie_pme.c
> ===================================================================
> --- linux-2.6.orig/drivers/pci/pcie/pme/pcie_pme.c
> +++ linux-2.6/drivers/pci/pcie/pme/pcie_pme.c
> @@ -147,6 +147,8 @@ static bool pcie_pme_walk_bus(struct pci
> /* Skip PCIe devices in case we started from a root port. */
> if (!pci_is_pcie(dev) && pci_check_pme_status(dev)) {
> pm_request_resume(&dev->dev);
> + if (device_may_wakeup(&dev->dev))
> + pm_wakeup_event(&dev->dev);
> ret = true;
> }
>
> Index: linux-2.6/drivers/base/power/power.h
> ===================================================================
> --- linux-2.6.orig/drivers/base/power/power.h
> +++ linux-2.6/drivers/base/power/power.h
> @@ -30,6 +30,9 @@ extern void device_pm_move_before(struct
> extern void device_pm_move_after(struct device *, struct device *);
> extern void device_pm_move_last(struct device *);
>
> +/* drivers/base/power/wakeup.c */
> +extern unsigned long pm_dev_wakeup_count(struct device *dev);
> +
> #else /* !CONFIG_PM_SLEEP */
>
> static inline void device_pm_init(struct device *dev)
> Index: linux-2.6/drivers/base/power/sysfs.c
> ===================================================================
> --- linux-2.6.orig/drivers/base/power/sysfs.c
> +++ linux-2.6/drivers/base/power/sysfs.c
> @@ -144,6 +144,14 @@ wake_store(struct device * dev, struct d
>
> static DEVICE_ATTR(wakeup, 0644, wake_show, wake_store);
>
> +static ssize_t wakeup_count_show(struct device *dev,
> + struct device_attribute *attr, char *buf)
> +{
> + return sprintf(buf, "%lu\n", pm_dev_wakeup_count(dev));
> +}
> +
> +static DEVICE_ATTR(wakeup_count, 0444, wakeup_count_show, NULL);
> +
> #ifdef CONFIG_PM_ADVANCED_DEBUG
> #ifdef CONFIG_PM_RUNTIME
>
> @@ -230,6 +238,7 @@ static struct attribute * power_attrs[]
> &dev_attr_control.attr,
> #endif
> &dev_attr_wakeup.attr,
> + &dev_attr_wakeup_count.attr,
> #ifdef CONFIG_PM_ADVANCED_DEBUG
> &dev_attr_async.attr,
> #ifdef CONFIG_PM_RUNTIME
>
--
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