[RFC]Something wrong with my module

On Thu, Apr 12, 2012 at 9:03 PM, Jonathan Neusch?fer
[off-list ref] wrote:

Hi Jonathan,

On Thu, Apr 12, 2012 at 06:16:56PM +0800, harryxiyou wrote:

quoted

Hi greg,

...

quoted

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.

Yup, you are right. I will correct it.

quoted

? ? ? }
? ? ? 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.

Hmmm.., i just want to give a simplest task_struct, which is my pcb structure.
Of course, it is bogus but it is now wrong for inserting. It can not
print my fields
correctly. (I run this module after i take away the rm_task function)

Some wrong logs like this:

[ 1515.054547] Search for insert task-------->
[ 1515.054550] pid: 1, state: 1, comm: init
[ 1515.054554] pid: 2, state: 1, comm: kthreadd
[ 1515.054558] pid: 3, state: 1, comm: ksoftirqd/0
[ 1515.054561] pid: 4, state: 1, comm: migration/0
[ 1515.054564] pid: 5, state: 1, comm: watchdog/0
[ 1515.054568] pid: 6, state: 1, comm: events/0
[ 1515.054571] pid: 7, state: 1, comm: cpuset
[ 1515.054575] pid: 8, state: 1, comm: khelper
...
[ 1515.055011] pid: 2117, state: 1, comm: bash
[ 1515.055014] pid: 2234, state: 1, comm: vim
[ 1515.055017] pid: 2236, state: 1, comm: flush-8:0
[ 1515.055020] pid: 2370, state: 1, comm: su
[ 1515.055023] pid: 2377, state: 1, comm: bash
[ 1515.055027] pid: 2701, state: 0, comm: insmod
[ 1515.055030] the number of process is 144
[ 1515.055032] show all tasks-------->
[ 1515.055035] pid: 1, state: 1, comm: init
[ 1515.055038] pid: 2, state: 1, comm: kthreadd
[ 1515.055041] pid: 3, state: 1, comm: ksoftirqd/0
[ 1515.055044] pid: 4, state: 1, comm: migration/0
[ 1515.055047] pid: 5, state: 1, comm: watchdog/0
[ 1515.055051] pid: 6, state: 1, comm: events/0
[ 1515.055054] pid: 7, state: 1, comm: cpuset
[ 1515.055057] pid: 8, state: 1, comm: khelper
[ 1515.055060] pid: 9, state: 1, comm: netns
[ 1515.055063] pid: 10, state: 1, comm: async/mgr
[ 1515.055066] pid: 11, state: 1, comm: pm
[ 1515.055069] pid: 12, state: 1, comm: sync_supers
[ 1515.055072] pid: 13, state: 1, comm: bdi-default
[ 1515.055075] pid: 14, state: 1, comm: kintegrityd/0
[ 1515.055078] pid: 15, state: 1, comm: kblockd/0
[ 1515.055081] pid: 16, state: 1, comm: ata_aux
[ 1515.055084] pid: 17, state: 1, comm: ata_sff/0
[ 1515.055087] pid: 18, state: 1, comm: khubd
[ 1515.055090] pid: 19, state: 1, comm: kseriod
[ 1515.055093] pid: 20, state: 1, comm: kmmcd
[ 1515.055096] pid: 22, state: 1, comm: khungtaskd
...
[ 1515.055466] pid: 2234, state: 1, comm: vim
[ 1515.055468] pid: 2236, state: 1, comm: flush-8:0
[ 1515.055472] pid: 2370, state: 1, comm: su
[ 1515.055474] pid: 2377, state: 1, comm: bash
[ 1515.055477] pid: 2701, state: 0, comm: insmod
[ 1515.055481] pid: 0, state: 1, comm:
[ 1515.055483] the number of process is 145

I give the pid 8, state 8, and comm "jiawei" in my module. But it can
not print correctly. Maybe kernel can tell my bogus one,right?

quoted

? ? ? 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.

quoted

? ? ? 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?

quoted

? ? ? printk("<1> Hello World\n");

The KERN_* constants are a good replacement for a manual "<n>".

Yup, that would be fine.

quoted

Dmesg logs:

[ 1174.738305] Search for insert task-------->

[...]

quoted

[ 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.

Hmm, it sounds well for me.

quoted

Cloud you please give me some help?

Hope This Helps,
? ? ? ?Jonathan Neusch?fer

It do helps me, thanks very much ;-)



-- 
Thanks
Harry Wei