Process Management – Simulate an Unkillable Process in D State

benchmarkprocessprocess-management

For catastrophe testing scenarios on out server environment we're looking for an easy way to make a process stuck in D (uninterruptible sleep) state.

Any easy ways? An example C sample code would be a plus 🙂

Edit – the first answer is semi-correct, as the process is shown to be in D state, but it still receives signals and can be killed

Best Answer

I had the same problem and resolved it by creating a kernel module that gets stuck in D state.

As I don't have any experience in modules, I took the code from this turorial with some modifications found someplace esle.

The result is a device on /dev/memory that gets stuck on read but can be waken up writting on it (it needs two writes, I don't know why but I don't care).

To use it just:

# make
# make mknod
# make install
# cat /dev/memory   # this gets blocked

To unblock, from another terminal:

# echo -n a > /dev/memory
# echo -n a > /dev/memory

Makefile:

obj-m += memory.o

all:
    make -C /lib/modules/$(shell uname -r)/build M=$(PWD) modules

clean:
    make -C /lib/modules/$(shell uname -r)/build M=$(PWD) clean

install:
    sudo insmod memory.ko

uninstall:
    sudo rmmod memory

mknod:
    sudo mknod /dev/memory c 60 0
    sudo chmod 666 /dev/memory

Code for memory.c:

/* Necessary includes for device drivers */
#include <linux/init.h>
#include <linux/module.h>
#include <linux/kernel.h> /* printk() */
#include <linux/slab.h> /* kmalloc() */
#include <linux/fs.h> /* everything... */
#include <linux/errno.h> /* error codes */
#include <linux/types.h> /* size_t */
#include <linux/proc_fs.h>
#include <linux/fcntl.h> /* O_ACCMODE */
#include <asm/uaccess.h> /* copy_from/to_user */
#include <linux/sched.h>

MODULE_LICENSE("Dual BSD/GPL");

/* Declaration of memory.c functions */
int memory_open(struct inode *inode, struct file *filp);
int memory_release(struct inode *inode, struct file *filp);
ssize_t memory_read(struct file *filp, char *buf, size_t count, loff_t *f_pos);
ssize_t memory_write(struct file *filp, char *buf, size_t count, loff_t *f_pos);
void memory_exit(void);
int memory_init(void);

/* Structure that declares the usual file */
/* access functions */
ssize_t memory_write( struct file *filp, char *buf, size_t count, loff_t *f_pos);
ssize_t memory_read(struct file *filp, char *buf, size_t count, loff_t *f_pos);
int memory_open(struct inode *inode, struct file *filp);
int memory_release(struct inode *inode, struct file *filp);
struct file_operations memory_fops = {
    .read = memory_read,
    .write = memory_write,
    .open = memory_open,
    .release = memory_release
};

/* Declaration of the init and exit functions */
module_init(memory_init);
module_exit(memory_exit);

/* Global variables of the driver */
/* Major number */
int memory_major = 60;
/* Buffer to store data */
char *memory_buffer;

int memory_init(void) {
    int result;

    /* Registering device */
    result = register_chrdev(memory_major, "memory", &memory_fops);
    if (result < 0) {
        printk(
                "<1>memory: cannot obtain major number %d\n", memory_major);
        return result;
    }

    /* Allocating memory for the buffer */
    memory_buffer = kmalloc(1, GFP_KERNEL); 
    if (!memory_buffer) { 
        result = -ENOMEM;
        goto fail; 
    } 
    memset(memory_buffer, 0, 1);

    printk("<1>Inserting memory module\n"); 
    return 0;

fail: 
    memory_exit(); 
    return result;
}

void memory_exit(void) {
    /* Freeing the major number */
    unregister_chrdev(memory_major, "memory");

    /* Freeing buffer memory */
    if (memory_buffer) {
        kfree(memory_buffer);
    }

    printk("<1>Removing memory module\n");

}

int memory_open(struct inode *inode, struct file *filp) {

    /* Success */
    return 0;
}

int memory_release(struct inode *inode, struct file *filp) {

    /* Success */
    return 0;
}
static DECLARE_WAIT_QUEUE_HEAD(wq);
static volatile int flag = 0;

ssize_t memory_read(struct file *filp, char *buf, 
        size_t count, loff_t *f_pos) { 

    printk("<1>going to sleep\n");
    flag = 0;
    //wait_event_interruptible(wq, flag != 0);
    wait_event(wq, flag != 0);

    printk("<1>Reading from memory module\n");
    /* Transfering data to user space */ 
    copy_to_user(buf,memory_buffer,1);

    /* Changing reading position as best suits */ 
    if (*f_pos == 0) { 
        *f_pos+=1; 
        return 1; 
    } else { 
        return 0; 
    }
}

ssize_t memory_write( struct file *filp, char *buf,
        size_t count, loff_t *f_pos) {

    char *tmp;

    printk("<1>wake someone up\n");
    flag = 1;
    //wake_up_interruptible(&wq);
    wake_up(&wq);

    printk("<1>Writting to memory module\n");
    tmp=buf+count-1;
    copy_from_user(memory_buffer,tmp,1);
    return 1;
}
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