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