vfree in timerfunciton causes kernel crash

vfree in timerfunciton causes kernel crash

[Mikkel Christiansen]

[-- Attachment #1: Type: text/plain, Size: 402 bytes --]

Hi

Idea: a module allocates memory (vmalloc) for userspace program which 
then craches.
Due to lack of activity timer is  expires and free's the unused memory 
(vfree).
(see tc_core.c later in this mail for details)

Problem: when timer expires and vfree is called then kernel crashes -
or rather freezes silently.

Can anyone explain why this happens? a kernel bug?

Cheers
    Mikkel

kernel 2.6.5


[-- Attachment #2: tf_core.c --]
[-- Type: text/x-c, Size: 816 bytes --]

#include <linux/module.h>
#include <linux/kernel.h>
#include <linux/init.h>
#include <linux/spinlock.h>
#include <linux/vmalloc.h>
#include <linux/timer.h>
#include <linux/sched.h>

#define MODULE_NAME "tf"

#ifdef __KERNEL__

int *buf;
struct timer_list timer;

static void timeoutfun(unsigned long b) {
  printk("tf: timeoutfun\n");
  vfree(buf);
}

struct timer_list timer;

int __init init_tf(void)
{
  printk("init_tf\n");
  buf = vmalloc(10*sizeof(int));
  
  init_timer(&timer); /* Initialization of the timer */
  
  timer.function = &timeoutfun;
  timer.data     = 10;
  timer.expires  = jiffies + (10 * HZ); /* 1 sec */
  
  add_timer(&timer);

  return 0;
}


void __exit exit_tf(void)
{
  printk("exit_tf\n");
  vfree(buf);
}


module_init(init_tf);
module_exit(exit_tf);
MODULE_LICENSE("GPL");


#endif

[-- Attachment #3: Makefile --]
[-- Type: text/plain, Size: 182 bytes --]

KERNEL_SOURCE = /home/mixxel/pack/linux-2.6.4
PWD = `pwd`
obj-m := tf.o

tf-objs := tf_core.o 

default: 
	make -C ${KERNEL_SOURCE} SUBDIRS=${PWD} modules

clean:
	rm *.{o,ko} .*.cmd

Re: vfree in timerfunciton causes kernel crash

[William Lee Irwin III]

On Fri, Apr 16, 2004 at 06:10:50PM +0200, Mikkel Christiansen wrote:
> Idea: a module allocates memory (vmalloc) for userspace program which 
> then craches.
> Due to lack of activity timer is  expires and free's the unused memory 
> (vfree).
> (see tc_core.c later in this mail for details)
> Problem: when timer expires and vfree is called then kernel crashes -
> or rather freezes silently.
> Can anyone explain why this happens? a kernel bug?
> Cheers
>    Mikkel
> kernel 2.6.5

Use schedule_work() to do this from process context. It's a programming
error (specifically a deadlock) to vfree() from interrupt context or with
interrupts disabled.


-- wli