概述
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!
代码
#include<linux/init.h> #include<linux/module.h> #include<linux/kernel.h> #include<linux/list.h> #include<linux/cpumask.h> 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");
内核
@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