内核为2.6.32。
卸载模块target时,不管是否为强制卸载,都输出:
ERROR:Module target is in use.
用lsmod查看target,发现Used by计数为1,而据我所知,没有其它模块依赖target。
编写模块检查target的module结构,发现:
target->state == 0 // 模块存活
module_refcount(target) == 1 // 模块引用计数为1
list_empty(target->modules_which_use_me) == 1 // 模块依赖列表为空
这个就很奇怪,模块的引用计数为1,却没有引用者。
这可能是模块插入内核时出错而引起的,这里先不研究,先关注怎么把它强制卸载掉,虽然
insmod加载是临时的,所以通过重启电脑可以解决一些问题,但是不能总是依靠重启啊。
解决方法:编写模块mymod中把问题模块target的引用计数置为0,就可以顺利卸载掉target了!
#include
#include
#include
#include
#include
static int __init mymod_init(void)
{
struct module *mod,*relate;
int cpu;
// 打印本模块的模块名和模块状态
printk(KERN_ALERT"[insmod mymod] name:%s state:%d\n",THIS_MODULE->name,THIS_MODULE->state);
// 遍历模块列表,查找target模块
list_for_each_entry(mod,THIS_MODULE->list.prev,list)
{
if(strcmp(mod->name,"target")==0) {
// 打印target的模块名、模块状态、引用计数
printk(KERN_ALERT"name:%s state:%d refcnt:%u ",mod->name,mod->state,module_refcount(mod));
// 打印出所有依赖target的模块名
if(!list_empty(&mod->modules_which_use_me)) {
list_for_each_entry(relate,&mod->modules_which_use_me,modules_which_use_me)
printk(KERN_ALERT"%s ",relate->name);
} else
printk(KERN_ALERT"used by NULL\n");
// 把target的引用计数置为0
for_each_possible_cpu(cpu)
local_set(__module_ref_addr(mod,cpu),0);
// 再看看target的名称、状态、引用计数
printk(KERN_ALERT"name:%s state:%d refcnt:%u\n",mod->name,mod->state,module_refcount(mod));
}
}
return 0;
}
static void __exit mymod_exit(void)
{
printk(KERN_ALERT"[rmmod mymod] name:%s state:%d\n",THIS_MODULE->name,THIS_MODULE->state);
}
module_init(mymod_init);
module_exit(mymod_exit);
MODULE_AUTHOR("Zhangsk");
MODULE_LICENSE("GPL");
MODULE_DESCRIPTION("Why module can not be removed");
@include/linux/module.h:
extern struct module __this_module;
#define THIS_MODULE (&__this_module);
enum module_state{
MODULE_STATE_LIVE; // 模块存活,0
MODULE_STATE_COMING; // 正在加载模块,1
MODULE_STATE_GOING; // 正在卸载模块,2
};
struct module {
enum module_state state; // 模块状态
/* Member of list of modules */
struct list_head list; // 内核模块链表
/* Unique handle for this module */
char name[MODULE_NAME_LEN]; //模块名称
...
#ifdef CONFIG_MODULE_UNLOAD
/* What modules depend on me? */
struct list_head modules_which_use_me;
/* Who is waiting for us to be unloaded */
struct task_struct *waiter;
/* Destruction function. */
void (*exit) (void);
#ifdef CONFIG_SMP
char *refptr;
#else
local_t ref;
#endif
#endif
...
};
static inline local_t *__module_ref_addr(struct module *mod, int cpu)
{#ifdef CONFIG_SMP
return (local_t *) (mod->refptr + per_cpu_offset(cpu));
#else
return &mod->ref;
#endif
}
@include/asm-generic/atomic.h:
typedef atomic64_t atomic_long_t;
@include/linux/types.h:
typedef struct {
volatile int counter;
} atomic_t;
#ifdef CONFIG_64BIT
typedef struct {
volatile long counter;
} atomic64_t;
#endif
@arch/x86/include/asm/local.h:
typedef struct {
atomic_long_t a;
} local_t;
#define local_read(l) atomic_long_read(&(l)->a)
#define local_set(l, i) atomic_long_set(&(l)->a, (i))
//此外还有加减操作
@include/asm-generic/percpu.h:
#ifdef CONFIG_SMP
/** per_cpu_offset() is the offset that has to be added to a percpu variable to get the instance for
* a certain processor. * Most arches use the __per_cpu_offset array for those offsets but some arches have their own
* ways of determining the offset (x86_64, s390).
*/
#ifndef __per_cpu_offset
extern unsigned long __per_cpu_offset[NR_CPUS];
#define per_cpu_offset(x) (__per_cpu_offset[x])
#endif