use copy_to_user fail in timer handler function,why? - c

Question

If I use copy_to_user in ioctl function, i can copy the data to the user space, but if I put the copy_to_user into the timeout handler function, copy_to_user can not be successful. Why?
#include <linux/init.h>
...
#define GLOBAL_MEMSIZE 0x1000//4K
...
static struct timer_list mytimer;
...
typedef struct globalmem_dev{
struct cdev cdev;
unsigned char mem[GLOBAL_MEMSIZE];
} Glo_dev, *Pglo_dev;
Pglo_dev globalmem_devp;//global pointer
If I put copy_to_user in here, I can not copy the data to user correctly
/*Timeout handler function*/
static void timer_func(unsigned long data)
{
int retc = 0;
retc = copy_to_user((void __user *)data, globalmem_devp->mem, 8);
if(retc)
{
printk("timer_func------->copy_to_user fail\n");
}
mod_timer(&mytimer, jiffies + 2*HZ);
}
/*file open function*/
static int hello_open(struct inode *inode, struct file *file)
{
printk("hello open!\n");
file->private_data = globalmem_devp;
return 0;
}
/*file close function*/
static int hello_release(struct inode *inode, struct file *file)
{
del_timer_sync(&mytimer);
printk("hello closed\n");
return 0;
}
The copy_to_user work fine in the ioctl function
/*ioctl*/
static long int globalmem_ioctl(struct file *file, unsigned int cmd, unsigned long arg)
{
/*if(copy_to_user((void __user *)arg, globlmem_devp->mem, 8))
{
printk("copy_to_user fial\n");
}*/
setup_timer(&mytimer, timer_func, arg);
mytimer.expires = jiffies + HZ;
add_timer(&mytimer);
return 0;
}
static struct file_operations hello_ops = {
...
};
/*init function*/
static int __init hello_init(void)
{
...
globalmem_devp = kmalloc(sizeof(Glo_dev), GFP_KERNEL);//
if(NULL == globalmem_devp)
{
return -ENOMEM;
}
...
return 0;
}
static void __exit hello_exit(void)
{
...
}
MODULE_LICENSE("GPL");
MODULE_AUTHOR("test");
module_init(hello_init);
module_exit(hello_exit);

Answer 1

copy_to_user() copies the data into the memory of the current user-space process, so it can be used only in some code that has been called from such a process.
An interrupt handler can run at any time, so there might be no current process, or worse, the current process is some other process.