[RFC]Something wrong with my module

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 Neusch?fer