使用mmap发生错误，谁知道这是怎么回事

字符驱动的mmap函数是这么写的：
static int  led_mmap (struct file *file, struct vm_area_struct *vma){
char *p;

int size = vma->vm_end - vma->vm_start;

p = (char *)vmalloc(PAGE_SIZE);
vma->vm_pgoff=(int)virt_to_phys(p)>>PAGE_SHIFT;
vma->vm_flags  ¦= VM_IO;

printk("\nled_mmap:%s[%d]:%s() mmap %dbytes\n",__FILE__,__LINE__,__FUNCTION__,size);
printk("mmap succeded size=%x\n",size);
printk(KERN_NOTICE "Simple VMA open, virt %lx, phys %lx\n", vma->vm_start, vma->vm_pgoff  < < PAGE_SHIFT);

if (remap_pfn_range(vma, vma->vm_start, vma->vm_pgoff,
    vma->vm_end - vma->vm_start,
    vma->vm_page_prot))
return -EAGAIN;



return 0;
}

应用程序是这些写的：
char *maddr;
int fd;
fd = open("/dev/led",O_RDONLY);
if(fd <0)exit(1);
maddr = mmap(NULL,0x100,  PROT_NONE, MAP_SHARED, fd,0);
printf("maddr=%x errno =%x\n", (int )maddr,errno);
           *maddr = 0;
        printf(" %.2x ",*(char *)maddr);


结果却是这样的，有谁知道这是怎么回事吗？
maddr=40006000 errno =0
Segmentation fault

出现了段错误，一般是内存访问出错造成的，可能是内存范围超出了