kernel crash for spinlock concurrency in linux-kernel - c

Question

I want to clear a list which type is defined by Kernel. I have two main structs, num_wrapper and num. num_wapper has a list of num, and kernel crashs when I do the del_all_node() function.
I try to mark the list_del, and the kernel will not be crash. I don't understand why there will be crash problem since I have use spin_lock to protect this num_list.
Any tips will be appreciate.
The following is the simplified code.
#include <linux/init.h>
#include <linux/module.h>
#include <linux/list.h>
#include <linux/slab.h>
struct num_wrapper {
struct list_head num_list;
spinlock_t list_lock;
u8 check_num;
};
struct num {
struct list_head node;
int number;
struct num_wrapper* num_w_ptr;
};
s32 del_all_node(struct num_wrapper *number_wrap)
{
struct num *tmp;
struct num *num_head;
spin_lock(&number_wrap->list_lock);
list_for_each_entry_safe(num_head, tmp, &number_wrap->num_list, node) {
printk("num_head is %d\n", num_head->number);
list_del(&num_head->node);//this line seems to have problem
}
spin_unlock(&number_wrap->list_lock);
return 0;
}
static int __init hello_init(void)
{
/*Setup Scenario*/
struct num_wrapper *number_wrap = kzalloc(sizeof(struct num_wrapper)
, GFP_KERNEL);
struct num *number = kzalloc(sizeof(struct num), GFP_KERNEL);
number->number = 10;
number_wrap->check_num = 20;
INIT_LIST_HEAD(&number->node);
INIT_LIST_HEAD(&number_wrap->num_list);
list_add_tail(&number->node, &number_wrap->num_list);
del_all_node(number_wrap);
return 0;
}
static void hello_exit(void)
{
printk(KERN_ALERT "Good, haha\n");
}
module_init(hello_init);
module_exit(hello_exit);
update
After doing some debug, I seems to find root cause...
my scenario is as follows :
I have a private data struct which is included in the net_device struct.
And the following is the simplified scenario:
struct xx_if *xx_if; //this is private data in net_device
struct xx_if *tmp;
list_for_each_entry_safe(xx_if, tmp, xx_if_wrap->if_list, list) {
free_netdev(xx_if->ndev);
list_del(&xx_if->list);
}
Since free_netdev will also free the private data xx_if, the code broken...
My fix is change the sequence to these two statements, and it fix the crash problem.
Still strange thing is I have check whether xx_if is NULL, but still lead to crash if I don't interchange these two statements.

Answer 1

I don't clearly understand following code:
INIT_LIST_HEAD(&number->node);
INIT_LIST_HEAD(&number_wrap->num_list);
list_add_tail(&number->node, &number_wrap->num_list);
You init two different structures, then you add one type of list to another type of list.
Is that the way you can do?
I think, that you need something like this:
struct num{
u8 check_num;
struct list_head list;
};
struct num_wrapper{
struct num* num_ptr;
spinlock_t list_lock;
};
int init_num_wrapper(struct num_wrapper** prt){
if(!ptr && *ptr){
return -EINVAL;
}
*ptr = kzalloc(sizeof(struct num_wrapper), GFP_KERNEL);
if(!*ptr){
return -ENOMEM;
}
INIT_LIST_HEAD(& (*ptr)->num_ptr->list);
... init spinlock
return 0;
}
int add_num(num_wrapper* prt_wrap, u8 check_num){
... checking pointers
struct num num* = NULL;
num = kmalloc(sizeof(struct num), GFP_KERNEL);
if(! num){
return -ENOMEM;
}
INIT_LIST_HEAD(&num->list);
num->check_num = check_num;
spin_lock(&prt_wrap->list_lock);
list_add_tail(&num->list, &prt_wrap->num_ptr.list);
spin_unlock(&prt_wrap->list_lock);
return 0;
}
int remove_all_nodes(num_wrapper* prt_wrap){
... checking pointer
struct num *tmp = NULL;
struct num *num_head = NULL;
spin_lock(&number_wrap->list_lock);
list_for_each_entry_safe(num_head, tmp, &prt_wrap->list, list)
{
printk("num_head is %d\n", num_head->number);
list_del(&num_head->node);//this line seems to have problem
}
spin_unlock(&num_wrapper->list_lock);
return 0;
}
Update
Then, you can use above functions for manipulating of num_wrapper.
For example:
//...
struct num_wrapper* nums = NULL;
init_num_wrapper(&nums); // after this call, you will have inited nums var, which can be used with others functions for manipulating with num_wrapper list.
u8 num = 2;
add_num(nums, num); // after this call new node with num will be added to num_wrapper
//...