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    Subject[PATCH 2/4] PM: Reference counting of power.subsys_data
    Date
    From: Rafael J. Wysocki <rjw@sisk.pl>

    Since the power.subsys_data device field will be used by multiple
    filesystems, introduce a reference counting mechanism for it to avoid
    freeing it prematurely or changing its value at a wrong time.

    Make the PM clocks management code that currently is the only user of
    power.subsys_data use the new reference counting.

    Signed-off-by: Rafael J. Wysocki <rjw@sisk.pl>
    ---
    drivers/base/power/Makefile | 2
    drivers/base/power/clock_ops.c | 24 ++---------
    drivers/base/power/common.c | 86 +++++++++++++++++++++++++++++++++++++++++
    include/linux/pm.h | 3 +
    4 files changed, 95 insertions(+), 20 deletions(-)

    Index: linux-2.6/drivers/base/power/common.c
    ===================================================================
    --- /dev/null
    +++ linux-2.6/drivers/base/power/common.c
    @@ -0,0 +1,86 @@
    +/*
    + * drivers/base/power/common.c - Common device power management code.
    + *
    + * Copyright (C) 2011 Rafael J. Wysocki <rjw@sisk.pl>, Renesas Electronics Corp.
    + *
    + * This file is released under the GPLv2.
    + */
    +
    +#include <linux/init.h>
    +#include <linux/kernel.h>
    +#include <linux/slab.h>
    +#include <linux/device.h>
    +#include <linux/pm_runtime.h>
    +
    +/**
    + * dev_pm_get_subsys_data - Create or refcount power.subsys_data for device.
    + * @dev: Device to handle.
    + *
    + * If power.subsys_data is NULL, point it to a new object, otherwise increment
    + * its reference counter. Return 1 if a new object has been created, otherwise
    + * return 0 or error code.
    + */
    +int dev_pm_get_subsys_data(struct device *dev)
    +{
    + struct pm_subsys_data *psd;
    + int ret = 0;
    +
    + psd = kzalloc(sizeof(*psd), GFP_KERNEL);
    + if (!psd)
    + return -ENOMEM;
    +
    + spin_lock_irq(&dev->power.lock);
    +
    + if (dev->power.subsys_data) {
    + dev->power.subsys_data->refcount++;
    + } else {
    + mutex_init(&psd->lock);
    + psd->refcount = 1;
    + dev->power.subsys_data = psd;
    + pm_clk_init(dev);
    + psd = NULL;
    + ret = 1;
    + }
    +
    + spin_unlock_irq(&dev->power.lock);
    +
    + /* kfree() verifies that its argument is nonzero. */
    + kfree(psd);
    +
    + return ret;
    +}
    +EXPORT_SYMBOL_GPL(dev_pm_get_subsys_data);
    +
    +/**
    + * dev_pm_put_subsys_data - Drop reference to power.subsys_data.
    + * @dev: Device to handle.
    + *
    + * If the reference counter of power.subsys_data is zero after dropping the
    + * reference, power.subsys_data is removed. Return 1 if that happens or 0
    + * otherwise.
    + */
    +int dev_pm_put_subsys_data(struct device *dev)
    +{
    + struct pm_subsys_data *psd;
    + int ret = 0;
    +
    + spin_lock_irq(&dev->power.lock);
    +
    + psd = dev_to_psd(dev);
    + if (!psd) {
    + ret = -EINVAL;
    + goto out;
    + }
    +
    + if (--psd->refcount == 0) {
    + dev->power.subsys_data = NULL;
    + kfree(psd);
    + ret = 1;
    + }
    +
    + out:
    + spin_unlock_irq(&dev->power.lock);
    +
    + return ret;
    +}
    +EXPORT_SYMBOL_GPL(dev_pm_put_subsys_data);
    Index: linux-2.6/include/linux/pm.h
    ===================================================================
    --- linux-2.6.orig/include/linux/pm.h
    +++ linux-2.6/include/linux/pm.h
    @@ -424,6 +424,7 @@ struct wakeup_source;

    struct pm_subsys_data {
    struct mutex lock;
    + unsigned int refcount;
    #ifdef CONFIG_PM_CLK
    struct list_head clock_list;
    #endif
    @@ -474,6 +475,8 @@ struct dev_pm_info {
    };

    extern void update_pm_runtime_accounting(struct device *dev);
    +extern int dev_pm_get_subsys_data(struct device *dev);
    +extern int dev_pm_put_subsys_data(struct device *dev);

    /*
    * Power domains provide callbacks that are executed during system suspend,
    Index: linux-2.6/drivers/base/power/Makefile
    ===================================================================
    --- linux-2.6.orig/drivers/base/power/Makefile
    +++ linux-2.6/drivers/base/power/Makefile
    @@ -1,4 +1,4 @@
    -obj-$(CONFIG_PM) += sysfs.o generic_ops.o
    +obj-$(CONFIG_PM) += sysfs.o generic_ops.o common.o
    obj-$(CONFIG_PM_SLEEP) += main.o wakeup.o
    obj-$(CONFIG_PM_RUNTIME) += runtime.o
    obj-$(CONFIG_PM_TRACE_RTC) += trace.o
    Index: linux-2.6/drivers/base/power/clock_ops.c
    ===================================================================
    --- linux-2.6.orig/drivers/base/power/clock_ops.c
    +++ linux-2.6/drivers/base/power/clock_ops.c
    @@ -140,12 +140,8 @@ void pm_clk_remove(struct device *dev, c
    void pm_clk_init(struct device *dev)
    {
    struct pm_subsys_data *psd = dev_to_psd(dev);
    -
    - if (!psd)
    - return;
    -
    - INIT_LIST_HEAD(&psd->clock_list);
    - mutex_init(&psd->lock);
    + if (psd)
    + INIT_LIST_HEAD(&psd->clock_list);
    }

    /**
    @@ -157,16 +153,8 @@ void pm_clk_init(struct device *dev)
    */
    int pm_clk_create(struct device *dev)
    {
    - struct pm_subsys_data *psd;
    -
    - psd = kzalloc(sizeof(*psd), GFP_KERNEL);
    - if (!psd) {
    - dev_err(dev, "Not enough memory for PM clock data.\n");
    - return -ENOMEM;
    - }
    - dev->power.subsys_data = psd;
    - pm_clk_init(dev);
    - return 0;
    + int ret = dev_pm_get_subsys_data(dev);
    + return ret < 0 ? ret : 0;
    }

    /**
    @@ -185,8 +173,6 @@ void pm_clk_destroy(struct device *dev)
    if (!psd)
    return;

    - dev->power.subsys_data = NULL;
    -
    mutex_lock(&psd->lock);

    list_for_each_entry_safe_reverse(ce, c, &psd->clock_list, node)
    @@ -194,7 +180,7 @@ void pm_clk_destroy(struct device *dev)

    mutex_unlock(&psd->lock);

    - kfree(psd);
    + dev_pm_put_subsys_data(dev);
    }

    #endif /* CONFIG_PM */


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