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SubjectRe: [patch 02/28] pm_qos: clean up racy global "name" variable


On Sat, 10 Oct 2009, Thomas Gleixner wrote:

> "name" is a poor name for a file-global variable. It was used in three
> different functions, with no mutual exclusion. But it's just a tiny,
> temporary string; let's just move it onto the stack in the functions that
> need it. Also use snprintf() just in case.
>
> Signed-off-by: Jonathan Corbet <corbet@lwn.net>
> Cc: Mark Gross <mgross@linux.intel.com>
> Reviewed-by: Frederic Weisbecker <fweisbec@gmail.com>
> Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
>
> diff --git a/kernel/pm_qos_params.c b/kernel/pm_qos_params.c
> index d96b83e..3db49b9 100644
> --- a/kernel/pm_qos_params.c
> +++ b/kernel/pm_qos_params.c
> @@ -343,18 +343,18 @@ int pm_qos_remove_notifier(int pm_qos_class, struct notifier_block *notifier)
> }
> EXPORT_SYMBOL_GPL(pm_qos_remove_notifier);
>
> -#define PID_NAME_LEN sizeof("process_1234567890")
> -static char name[PID_NAME_LEN];
> +#define PID_NAME_LEN 32

Hmnn, why 32? Seems arbitrary. At least you see with "process_1234567890"
which is 19, an attempt to show what the maximum string size would be. If
a system were configured to enlarge the maximum PID from 32767 to 4194303
that would still only be 7 digits, so "process_1234567" - which is 16
digits with the newline would enough.

So, I suggest you change that to
#define PID_NAME_LEN sizeof("process_1234567")

Other than that, Reviewed-by: John Kacur <jkacur@redhat.com>

>
> static int pm_qos_power_open(struct inode *inode, struct file *filp)
> {
> int ret;
> long pm_qos_class;
> + char name[PID_NAME_LEN];
>
> pm_qos_class = find_pm_qos_object_by_minor(iminor(inode));
> if (pm_qos_class >= 0) {
> filp->private_data = (void *)pm_qos_class;
> - sprintf(name, "process_%d", current->pid);
> + snprintf(name, PID_NAME_LEN, "process_%d", current->pid);
> ret = pm_qos_add_requirement(pm_qos_class, name,
> PM_QOS_DEFAULT_VALUE);
> if (ret >= 0)
> @@ -366,9 +366,10 @@ static int pm_qos_power_open(struct inode *inode, struct file *filp)
> static int pm_qos_power_release(struct inode *inode, struct file *filp)
> {
> int pm_qos_class;
> + char name[PID_NAME_LEN];
>
> pm_qos_class = (long)filp->private_data;
> - sprintf(name, "process_%d", current->pid);
> + snprintf(name, PID_NAME_LEN, "process_%d", current->pid);
> pm_qos_remove_requirement(pm_qos_class, name);
>
> return 0;
> @@ -379,13 +380,14 @@ static ssize_t pm_qos_power_write(struct file *filp, const char __user *buf,
> {
> s32 value;
> int pm_qos_class;
> + char name[PID_NAME_LEN];
>
> pm_qos_class = (long)filp->private_data;
> if (count != sizeof(s32))
> return -EINVAL;
> if (copy_from_user(&value, buf, sizeof(s32)))
> return -EFAULT;
> - sprintf(name, "process_%d", current->pid);
> + snprintf(name, PID_NAME_LEN, "process_%d", current->pid);
> pm_qos_update_requirement(pm_qos_class, name, value);
>
> return sizeof(s32);
>
>
>


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