On Wednesday, September 19, 2012, Jean Pihet wrote:
> The per-device PM QoS locking requires a spinlock to be used. The reasons
> are:
> - an alignement with the PM QoS core code, which is used by the per-device
> PM QoS code for the constraints lists management. The PM QoS core code
> uses spinlocks to protect the constraints lists,
> - some drivers need to use the per-device PM QoS functionality from
> interrupt context or spinlock protected context.
> An example of such a driver is the OMAP HSI (high-speed synchronous serial
> interface) driver which needs to control the IP block idle state
> depending on the FIFO empty state, from interrupt context.
>
> Reported-by: Djamil Elaidi <d-elaidi@xxxxxx>
> Signed-off-by: Jean Pihet <j-pihet@xxxxxx>
Applied to the linux-next branch of the linux-pm.git tree as v3.7 material.
Next time please send CCs to linux-pm@xxxxxxxxxxxxxxx instead of the
Linux Foundation list (of the same name), which has been abandoned.
Thanks,
Rafael
> ---
> drivers/base/power/qos.c | 67 ++++++++++++++++++++++++++++------------------
> 1 files changed, 41 insertions(+), 26 deletions(-)
>
> diff --git a/drivers/base/power/qos.c b/drivers/base/power/qos.c
> index 74a67e0..968a771 100644
> --- a/drivers/base/power/qos.c
> +++ b/drivers/base/power/qos.c
> @@ -24,26 +24,32 @@
> * . a system-wide notification callback using the dev_pm_qos_*_global_notifier
> * API. The notification chain data is stored in a static variable.
> *
> - * Note about the per-device constraint data struct allocation:
> - * . The per-device constraints data struct ptr is tored into the device
> + * Notes about the per-device constraint data struct allocation:
> + * . The per-device constraints data struct ptr is stored into the device
> * dev_pm_info.
> * . To minimize the data usage by the per-device constraints, the data struct
> - * is only allocated at the first call to dev_pm_qos_add_request.
> + * is only allocated at the first call to dev_pm_qos_add_request.
> * . The data is later free'd when the device is removed from the system.
> - * . A global mutex protects the constraints users from the data being
> - * allocated and free'd.
> + *
> + * Notes about locking:
> + * . The dev->power.lock lock protects the constraints list
> + * (dev->power.constraints) allocation and free, as triggered by the
> + * driver core code at device insertion and removal,
> + * . A global lock dev_pm_qos_lock protects the constraints list entries
> + * from any modification and the notifiers registration and unregistration.
> + * . For both locks a spinlock is needed since this code can be called from
> + * interrupt context or spinlock protected context.
> */
>
> #include <linux/pm_qos.h>
> #include <linux/spinlock.h>
> #include <linux/slab.h>
> #include <linux/device.h>
> -#include <linux/mutex.h>
> #include <linux/export.h>
>
> #include "power.h"
>
> -static DEFINE_MUTEX(dev_pm_qos_mtx);
> +static DEFINE_SPINLOCK(dev_pm_qos_lock);
>
> static BLOCKING_NOTIFIER_HEAD(dev_pm_notifiers);
>
> @@ -110,18 +116,19 @@ static int apply_constraint(struct dev_pm_qos_request *req,
> * @dev: device to allocate data for
> *
> * Called at the first call to add_request, for constraint data allocation
> - * Must be called with the dev_pm_qos_mtx mutex held
> + * Must be called with the dev_pm_qos_lock lock held
> */
> static int dev_pm_qos_constraints_allocate(struct device *dev)
> {
> struct pm_qos_constraints *c;
> struct blocking_notifier_head *n;
> + unsigned long flags;
>
> - c = kzalloc(sizeof(*c), GFP_KERNEL);
> + c = kzalloc(sizeof(*c), GFP_ATOMIC);
> if (!c)
> return -ENOMEM;
>
> - n = kzalloc(sizeof(*n), GFP_KERNEL);
> + n = kzalloc(sizeof(*n), GFP_ATOMIC);
> if (!n) {
> kfree(c);
> return -ENOMEM;
> @@ -134,9 +141,9 @@ static int dev_pm_qos_constraints_allocate(struct device *dev)
> c->type = PM_QOS_MIN;
> c->notifiers = n;
>
> - spin_lock_irq(&dev->power.lock);
> + spin_lock_irqsave(&dev->power.lock, flags);
> dev->power.constraints = c;
> - spin_unlock_irq(&dev->power.lock);
> + spin_unlock_irqrestore(&dev->power.lock, flags);
>
> return 0;
> }
> @@ -150,10 +157,12 @@ static int dev_pm_qos_constraints_allocate(struct device *dev)
> */
> void dev_pm_qos_constraints_init(struct device *dev)
> {
> - mutex_lock(&dev_pm_qos_mtx);
> + unsigned long flags;
> +
> + spin_lock_irqsave(&dev_pm_qos_lock, flags);
> dev->power.constraints = NULL;
> dev->power.power_state = PMSG_ON;
> - mutex_unlock(&dev_pm_qos_mtx);
> + spin_unlock_irqrestore(&dev_pm_qos_lock, flags);
> }
>
> /**
> @@ -166,6 +175,7 @@ void dev_pm_qos_constraints_destroy(struct device *dev)
> {
> struct dev_pm_qos_request *req, *tmp;
> struct pm_qos_constraints *c;
> + unsigned long flags;
>
> /*
> * If the device's PM QoS resume latency limit has been exposed to user
> @@ -173,7 +183,7 @@ void dev_pm_qos_constraints_destroy(struct device *dev)
> */
> dev_pm_qos_hide_latency_limit(dev);
>
> - mutex_lock(&dev_pm_qos_mtx);
> + spin_lock_irqsave(&dev_pm_qos_lock, flags);
>
> dev->power.power_state = PMSG_INVALID;
> c = dev->power.constraints;
> @@ -198,7 +208,7 @@ void dev_pm_qos_constraints_destroy(struct device *dev)
> kfree(c);
>
> out:
> - mutex_unlock(&dev_pm_qos_mtx);
> + spin_unlock_irqrestore(&dev_pm_qos_lock, flags);
> }
>
> /**
> @@ -223,6 +233,7 @@ int dev_pm_qos_add_request(struct device *dev, struct dev_pm_qos_request *req,
> s32 value)
> {
> int ret = 0;
> + unsigned long flags;
>
> if (!dev || !req) /*guard against callers passing in null */
> return -EINVAL;
> @@ -233,7 +244,7 @@ int dev_pm_qos_add_request(struct device *dev, struct dev_pm_qos_request *req,
>
> req->dev = dev;
>
> - mutex_lock(&dev_pm_qos_mtx);
> + spin_lock_irqsave(&dev_pm_qos_lock, flags);
>
> if (!dev->power.constraints) {
> if (dev->power.power_state.event == PM_EVENT_INVALID) {
> @@ -255,7 +266,7 @@ int dev_pm_qos_add_request(struct device *dev, struct dev_pm_qos_request *req,
> ret = apply_constraint(req, PM_QOS_ADD_REQ, value);
>
> out:
> - mutex_unlock(&dev_pm_qos_mtx);
> + spin_unlock_irqrestore(&dev_pm_qos_lock, flags);
>
> return ret;
> }
> @@ -280,6 +291,7 @@ int dev_pm_qos_update_request(struct dev_pm_qos_request *req,
> s32 new_value)
> {
> int ret = 0;
> + unsigned long flags;
>
> if (!req) /*guard against callers passing in null */
> return -EINVAL;
> @@ -288,7 +300,7 @@ int dev_pm_qos_update_request(struct dev_pm_qos_request *req,
> "%s() called for unknown object\n", __func__))
> return -EINVAL;
>
> - mutex_lock(&dev_pm_qos_mtx);
> + spin_lock_irqsave(&dev_pm_qos_lock, flags);
>
> if (req->dev->power.constraints) {
> if (new_value != req->node.prio)
> @@ -299,7 +311,7 @@ int dev_pm_qos_update_request(struct dev_pm_qos_request *req,
> ret = -ENODEV;
> }
>
> - mutex_unlock(&dev_pm_qos_mtx);
> + spin_unlock_irqrestore(&dev_pm_qos_lock, flags);
> return ret;
> }
> EXPORT_SYMBOL_GPL(dev_pm_qos_update_request);
> @@ -319,6 +331,7 @@ EXPORT_SYMBOL_GPL(dev_pm_qos_update_request);
> int dev_pm_qos_remove_request(struct dev_pm_qos_request *req)
> {
> int ret = 0;
> + unsigned long flags;
>
> if (!req) /*guard against callers passing in null */
> return -EINVAL;
> @@ -327,7 +340,7 @@ int dev_pm_qos_remove_request(struct dev_pm_qos_request *req)
> "%s() called for unknown object\n", __func__))
> return -EINVAL;
>
> - mutex_lock(&dev_pm_qos_mtx);
> + spin_lock_irqsave(&dev_pm_qos_lock, flags);
>
> if (req->dev->power.constraints) {
> ret = apply_constraint(req, PM_QOS_REMOVE_REQ,
> @@ -338,7 +351,7 @@ int dev_pm_qos_remove_request(struct dev_pm_qos_request *req)
> ret = -ENODEV;
> }
>
> - mutex_unlock(&dev_pm_qos_mtx);
> + spin_unlock_irqrestore(&dev_pm_qos_lock, flags);
> return ret;
> }
> EXPORT_SYMBOL_GPL(dev_pm_qos_remove_request);
> @@ -359,8 +372,9 @@ EXPORT_SYMBOL_GPL(dev_pm_qos_remove_request);
> int dev_pm_qos_add_notifier(struct device *dev, struct notifier_block *notifier)
> {
> int ret = 0;
> + unsigned long flags;
>
> - mutex_lock(&dev_pm_qos_mtx);
> + spin_lock_irqsave(&dev_pm_qos_lock, flags);
>
> if (!dev->power.constraints)
> ret = dev->power.power_state.event != PM_EVENT_INVALID ?
> @@ -370,7 +384,7 @@ int dev_pm_qos_add_notifier(struct device *dev, struct notifier_block *notifier)
> ret = blocking_notifier_chain_register(
> dev->power.constraints->notifiers, notifier);
>
> - mutex_unlock(&dev_pm_qos_mtx);
> + spin_unlock_irqrestore(&dev_pm_qos_lock, flags);
> return ret;
> }
> EXPORT_SYMBOL_GPL(dev_pm_qos_add_notifier);
> @@ -389,8 +403,9 @@ int dev_pm_qos_remove_notifier(struct device *dev,
> struct notifier_block *notifier)
> {
> int retval = 0;
> + unsigned long flags;
>
> - mutex_lock(&dev_pm_qos_mtx);
> + spin_lock_irqsave(&dev_pm_qos_lock, flags);
>
> /* Silently return if the constraints object is not present. */
> if (dev->power.constraints)
> @@ -398,7 +413,7 @@ int dev_pm_qos_remove_notifier(struct device *dev,
> dev->power.constraints->notifiers,
> notifier);
>
> - mutex_unlock(&dev_pm_qos_mtx);
> + spin_unlock_irqrestore(&dev_pm_qos_lock, flags);
> return retval;
> }
> EXPORT_SYMBOL_GPL(dev_pm_qos_remove_notifier);
>
