From: Paul Mackerras <paulus@samba.org>
Currently the device_pm_foo() functions are rather prone to deadlocks
during suspend/resume. This is because the dpm_sem is held for the
duration of device_suspend() and device_resume() as well as device_pm_add()
and device_pm_remove(). If for any reason you get a device addition or
removal triggered by a device's suspend or resume code, you get a deadlock.
(The classic example is a USB host adaptor resuming and discovering that
the mouse you used to have plugged in has gone away.)
This patch fixes the problem by using a separate semaphore, called
dpm_list_sem, to cover the places where we need the device pm lists to be
stable, and by being careful about how we traverse the lists on suspend and
resume. I have analysed the various cases that can occur and I am
confident that I have handled them all correctly. I posted this patch
together with a detailed analysis 10 days ago.
Signed-off-by Paul Mackerras <paulus@samba.org>
Signed-off-by: Andrew Morton <akpm@osdl.org>
---
25-akpm/drivers/base/power/main.c | 11 ++++----
25-akpm/drivers/base/power/power.h | 5 +++
25-akpm/drivers/base/power/resume.c | 16 ++++++++++--
25-akpm/drivers/base/power/suspend.c | 44 +++++++++++++++++++----------------
4 files changed, 49 insertions(+), 27 deletions(-)
diff -puN drivers/base/power/main.c~fix-deadlocks-on-dpm_sem drivers/base/power/main.c
--- 25/drivers/base/power/main.c~fix-deadlocks-on-dpm_sem 2004-10-21 21:24:27.613384904 -0700
+++ 25-akpm/drivers/base/power/main.c 2004-10-21 21:24:27.621383688 -0700
@@ -28,6 +28,7 @@ LIST_HEAD(dpm_off);
LIST_HEAD(dpm_off_irq);
DECLARE_MUTEX(dpm_sem);
+DECLARE_MUTEX(dpm_list_sem);
/*
* PM Reference Counting.
@@ -75,12 +76,12 @@ int device_pm_add(struct device * dev)
pr_debug("PM: Adding info for %s:%s\n",
dev->bus ? dev->bus->name : "No Bus", dev->kobj.name);
atomic_set(&dev->power.pm_users, 0);
- down(&dpm_sem);
+ down(&dpm_list_sem);
list_add_tail(&dev->power.entry, &dpm_active);
device_pm_set_parent(dev, dev->parent);
if ((error = dpm_sysfs_add(dev)))
list_del(&dev->power.entry);
- up(&dpm_sem);
+ up(&dpm_list_sem);
return error;
}
@@ -88,11 +89,11 @@ void device_pm_remove(struct device * de
{
pr_debug("PM: Removing info for %s:%s\n",
dev->bus ? dev->bus->name : "No Bus", dev->kobj.name);
- down(&dpm_sem);
+ down(&dpm_list_sem);
dpm_sysfs_remove(dev);
device_pm_release(dev->power.pm_parent);
- list_del(&dev->power.entry);
- up(&dpm_sem);
+ list_del_init(&dev->power.entry);
+ up(&dpm_list_sem);
}
diff -puN drivers/base/power/power.h~fix-deadlocks-on-dpm_sem drivers/base/power/power.h
--- 25/drivers/base/power/power.h~fix-deadlocks-on-dpm_sem 2004-10-21 21:24:27.615384600 -0700
+++ 25-akpm/drivers/base/power/power.h 2004-10-21 21:24:27.622383536 -0700
@@ -28,6 +28,11 @@ extern void device_shutdown(void);
extern struct semaphore dpm_sem;
/*
+ * Used to serialize changes to the dpm_* lists.
+ */
+extern struct semaphore dpm_list_sem;
+
+/*
* The PM lists.
*/
extern struct list_head dpm_active;
diff -puN drivers/base/power/resume.c~fix-deadlocks-on-dpm_sem drivers/base/power/resume.c
--- 25/drivers/base/power/resume.c~fix-deadlocks-on-dpm_sem 2004-10-21 21:24:27.616384448 -0700
+++ 25-akpm/drivers/base/power/resume.c 2004-10-21 21:24:27.622383536 -0700
@@ -31,16 +31,22 @@ int resume_device(struct device * dev)
void dpm_resume(void)
{
+ down(&dpm_list_sem);
while(!list_empty(&dpm_off)) {
struct list_head * entry = dpm_off.next;
struct device * dev = to_device(entry);
+
+ get_device(dev);
list_del_init(entry);
+ list_add_tail(entry, &dpm_active);
+ up(&dpm_list_sem);
if (!dev->power.prev_state)
resume_device(dev);
-
- list_add_tail(entry, &dpm_active);
+ down(&dpm_list_sem);
+ put_device(dev);
}
+ up(&dpm_list_sem);
}
@@ -76,9 +82,13 @@ void dpm_power_up(void)
{
while(!list_empty(&dpm_off_irq)) {
struct list_head * entry = dpm_off_irq.next;
+ struct device * dev = to_device(entry);
+
+ get_device(dev);
list_del_init(entry);
- resume_device(to_device(entry));
list_add_tail(entry, &dpm_active);
+ resume_device(dev);
+ put_device(dev);
}
}
diff -puN drivers/base/power/suspend.c~fix-deadlocks-on-dpm_sem drivers/base/power/suspend.c
--- 25/drivers/base/power/suspend.c~fix-deadlocks-on-dpm_sem 2004-10-21 21:24:27.618384144 -0700
+++ 25-akpm/drivers/base/power/suspend.c 2004-10-21 21:24:27.623383384 -0700
@@ -63,11 +63,6 @@ int suspend_device(struct device * dev,
* If we hit a failure with any of the devices, call device_resume()
* above to bring the suspended devices back to life.
*
- * Note this function leaves dpm_sem held to
- * a) block other devices from registering.
- * b) prevent other PM operations from happening after we've begun.
- * c) make sure we're exclusive when we disable interrupts.
- *
*/
int device_suspend(u32 state)
@@ -75,29 +70,40 @@ int device_suspend(u32 state)
int error = 0;
down(&dpm_sem);
- while(!list_empty(&dpm_active)) {
+ down(&dpm_list_sem);
+ while (!list_empty(&dpm_active) && error == 0) {
struct list_head * entry = dpm_active.prev;
struct device * dev = to_device(entry);
+
+ get_device(dev);
+ up(&dpm_list_sem);
+
error = suspend_device(dev, state);
- if (!error) {
- list_del(&dev->power.entry);
- list_add(&dev->power.entry, &dpm_off);
- } else if (error == -EAGAIN) {
- list_del(&dev->power.entry);
- list_add(&dev->power.entry, &dpm_off_irq);
- } else {
+ down(&dpm_list_sem);
+
+ /* Check if the device got removed */
+ if (!list_empty(&dev->power.entry)) {
+ /* Move it to the dpm_off or dpm_off_irq list */
+ if (!error) {
+ list_del(&dev->power.entry);
+ list_add(&dev->power.entry, &dpm_off);
+ } else if (error == -EAGAIN) {
+ list_del(&dev->power.entry);
+ list_add(&dev->power.entry, &dpm_off_irq);
+ error = 0;
+ }
+ }
+ if (error)
printk(KERN_ERR "Could not suspend device %s: "
"error %d\n", kobject_name(&dev->kobj), error);
- goto Error;
- }
+ put_device(dev);
}
- Done:
+ up(&dpm_list_sem);
+ if (error)
+ dpm_resume();
up(&dpm_sem);
return error;
- Error:
- dpm_resume();
- goto Done;
}
EXPORT_SYMBOL_GPL(device_suspend);
_