On Thu, Apr 12, 2012 at 06:16:56PM +0800, harryxiyou wrote:
> Hi greg,
>
> I write a module for inserting a PCB or delete a PCB to kernel's
> PCB tree, but when i run it something wrong happens to me like following.
> My environment is "Linux 10 2.6.35-22-generic #33-Ubuntu SMP Sun Sep
> 19 20:34:50 UTC 2010 i686 GNU/Linux"
>
> hw2.c
>
> #include <linux/module.h>
> #include <linux/kernel.h>
> #include <linux/init.h>
> #include <linux/sched.h>
> #include <linux/list.h>
> #include <linux/slab.h>
>
> struct pcb {
> int pid;
> int state;
> int flag;
> char *comm;
> struct list_head tasks;
> };
>
> static int insert_task(struct task_struct *p) {
> struct pcb *pcb1 = NULL;
> pcb1 = (struct pcb *)kmalloc(sizeof(struct pcb), GFP_KERNEL);
> if (NULL == pcb1) {
> printk("<0> kmalloc failed!\n");
If you don't return, you'll do an invalid memory access the next line.
> }
> pcb1->state = 8;
> pcb1->flag = 8;
> pcb1->pid= 2;
> pcb1->comm = "jiawei";
> list_add(&pcb1->tasks, &p->tasks);
You add your pcb structure to a list of struct task_structs, this looks
somewhat bogus.
> return 0;
> }
>
> static int rm_task(struct task_struct *p){
> struct task_struct *del = p;
> list_del(&p->tasks);
> // kfree(del);
> return 0;
> }
> #if 1
> static int print_pid(void) {
You do possibly destructive operations here, "print" doesn't quite imply
that.
> struct task_struct *task = NULL;
> struct task_struct *p = NULL;
> struct list_head *pos = NULL;
> int count = 0;
>
> printk("Search for insert task-------->\n");
> task = &init_task;
> list_for_each(pos, &task->tasks) {
> p = list_entry(pos, struct task_struct, tasks);
> count++;
> if (0 == p->pid) {
> rm_task(p);
> }
> printk("pid: %d, state: %ld, comm: %s\n", p->pid, p->state,
> p->comm);
> }
> insert_task(p);
Why do you want to insert your bogus struct after the last task?
> printk("<1> Hello World\n");
The KERN_* constants are a good replacement for a manual "<n>".
>
>
> Dmesg logs:
>
> [ 1174.738305] Search for insert task-------->
[...]
> [ 1174.738819] pid: 2481, state: 1, comm: bash
> [ 1174.738822] pid: 0, state: 1, comm:
> [ 1174.738840] BUG: unable to handle kernel paging request at 00100100
This is probably in insert_task.
list_del sets tasks->next to LIST_POISON1 (which is 0x00100100), list_add
tries to access it and segfaults.
>
> Cloud you please give me some help?
Hope This Helps,
Jonathan Neuschäfer
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