响应式网站建设的应用场景,怎么申请电商平台,南宁网红打卡,广州app开发网站建设文章参考Linux内核线程kernel thread详解 - 知乎 大概意思就是早期创建内核线程#xff0c;是交由内核处理#xff0c;由内核自己完成#xff08;感觉好像也不太对呢#xff09;#xff0c;创建一个内核线程比较麻烦#xff0c;会导致内核阻塞。因此就诞生了工作队列以及… 文章参考Linux内核线程kernel thread详解 - 知乎 大概意思就是早期创建内核线程是交由内核处理由内核自己完成感觉好像也不太对呢创建一个内核线程比较麻烦会导致内核阻塞。因此就诞生了工作队列以及现在的kthreadd 2号进程。这样我们在创建内核线程时只需要将消息告诉它们实际进行内核线程创建的任务有kthreadd完成感觉类似一个下半部。
我环境使用的是kthreadd进行内核线程的创建
内核线程创建kthread_create
kthread_create--kthread_create_on_node--__kthread_create_on_node
#define kthread_create(threadfn, data, namefmt, arg...) \kthread_create_on_node(threadfn, data, NUMA_NO_NODE, namefmt, ##arg) 可以看到这里只是将创建内核线程的任务加入了链表里面然后唤醒kthreadd进行内核线程的创建
struct task_struct *__kthread_create_on_node(int (*threadfn)(void *data),void *data, int node,const char namefmt[],va_list args)
{DECLARE_COMPLETION_ONSTACK(done);struct task_struct *task;struct kthread_create_info *create kmalloc(sizeof(*create),GFP_KERNEL);if (!create)return ERR_PTR(-ENOMEM);/* 被创建的内核线程的信息被存放到了create_info里面 */create-threadfn threadfn;create-data data;create-node node;create-done done;spin_lock(kthread_create_lock);/* 将create_info加入到链表中,然后唤醒kthreadd_task(2号进程)进行后续的内核线程创建 */list_add_tail(create-list, kthread_create_list);spin_unlock(kthread_create_lock);wake_up_process(kthreadd_task);/** Wait for completion in killable state, for I might be chosen by* the OOM killer while kthreadd is trying to allocate memory for* new kernel thread.*//* 这里是等待内核线程创建完成,内核线程创建完成后会释放这样完成量函数kthread里面会释放这个completion*/if (unlikely(wait_for_completion_killable(done))) {/** If I was SIGKILLed before kthreadd (or new kernel thread)* calls complete(), leave the cleanup of this structure to* that thread.*/if (xchg(create-done, NULL))return ERR_PTR(-EINTR);/** kthreadd (or new kernel thread) will call complete()* shortly.*/wait_for_completion(done);}/* 函数kthread里面会将result赋值为创建好的内核线程的task_struct */task create-result;if (!IS_ERR(task)) {static const struct sched_param param { .sched_priority 0 };char name[TASK_COMM_LEN];/** task is already visible to other tasks, so updating* COMM must be protected.*/vsnprintf(name, sizeof(name), namefmt, args);set_task_comm(task, name);//这里设置内核线程的名字/** root may have changed our (kthreadds) priority or CPU mask.* The kernel thread should not inherit these properties.*/sched_setscheduler_nocheck(task, SCHED_NORMAL, param);set_cpus_allowed_ptr(task, cpu_all_mask);}kfree(create);return task;
}
那2号进程kthreadd干了什么事情呢
2号进程在rest_init里面创建其处理函数为kthreadd
noinline void __ref rest_init(void)
{...............................pid kernel_thread(kthreadd, NULL, CLONE_FS | CLONE_FILES);rcu_read_lock();kthreadd_task find_task_by_pid_ns(pid, init_pid_ns);rcu_read_unlock();
............................
}
kthreadd--create_kthread--kernel_thread
int kthreadd(void *unused)
{struct task_struct *tsk current;/* Setup a clean context for our children to inherit. */set_task_comm(tsk, kthreadd);ignore_signals(tsk);set_cpus_allowed_ptr(tsk, cpu_all_mask);set_mems_allowed(node_states[N_MEMORY]);current-flags | PF_NOFREEZE;cgroup_init_kthreadd();/*其实就是一直检查kthread_create_list是否为空如果不为空将不断的处理链表里面的任务处理,创建内核线程*/for (;;) {set_current_state(TASK_INTERRUPTIBLE);if (list_empty(kthread_create_list))schedule();__set_current_state(TASK_RUNNING);spin_lock(kthread_create_lock);while (!list_empty(kthread_create_list)) {struct kthread_create_info *create;create list_entry(kthread_create_list.next,struct kthread_create_info, list);list_del_init(create-list);spin_unlock(kthread_create_lock);create_kthread(create);spin_lock(kthread_create_lock);}spin_unlock(kthread_create_lock);}return 0;
}
可以看到 内核线程的创建最终还是调用的kernel_thread。创建的内核线程会执行kthread在函数kthread里面执行了我们设置的内核线程处理函数threadfun
static void create_kthread(struct kthread_create_info *create)
{int pid;#ifdef CONFIG_NUMAcurrent-pref_node_fork create-node;
#endif/* We want our own signal handler (we take no signals by default). *//* 最终在kthread里面调用到我们设置的回调函数 */pid kernel_thread(kthread, create, CLONE_FS | CLONE_FILES | SIGCHLD);if (pid 0) {/* If user was SIGKILLed, I release the structure. */struct completion *done xchg(create-done, NULL);if (!done) {kfree(create);return;}create-result ERR_PTR(pid);complete(done);}
}
kthread运行线程处理函数
执行到这里,就算内核线程创建成功了.只不过它不会立即执行我们的threadfn(即创建内核线程时指定的函数)它会先释放completion并让出cpu。这就是kthread_create后还需要wake_up_process的原因。
static int kthread(void *_create)
{/* Copy data: its on kthreads stack */struct kthread_create_info *create _create;int (*threadfn)(void *data) create-threadfn;void *data create-data;struct completion *done;struct kthread *self;int ret;self kzalloc(sizeof(*self), GFP_KERNEL);set_kthread_struct(self);/* If user was SIGKILLed, I release the structure. *//* 将create-done赋值为NULL并返回create-done原来的值 */done xchg(create-done, NULL);if (!done) {kfree(create);do_exit(-EINTR);}if (!self) {create-result ERR_PTR(-ENOMEM);complete(done);do_exit(-ENOMEM);}self-data data;init_completion(self-exited);init_completion(self-parked);/* 此时的current就已经是我们创建好的内核线程了 */current-vfork_done self-exited;/* OK, tell user were spawned, wait for stop or wakeup */__set_current_state(TASK_UNINTERRUPTIBLE);//__kthread_create_on_node里面将result当做返回值的原因在这里体现create-result current;/* 在这里释放的completion,__kthread_create_on_node才会继续往下走 */complete(done);/*可以看到内核线程创建完了会先让出cpu,并不会立即执行我们的线程处理函数这就是我们为什么需要wake_up_process的原因,需要wake之后才会继续从这里执行然后走到我们的threadfn*/schedule();ret -EINTR;/*这个检查,我怀疑就是导致kthread_stop表现出不同行为的原因*/if (!test_bit(KTHREAD_SHOULD_STOP, self-flags)) {cgroup_kthread_ready();__kthread_parkme(self);/* 执行内核线程设置的处理函数 */ret threadfn(data);}/* 可以看到如果threadfn执行完了,内核线程退出是do_exit */do_exit(ret);
}
经过实际验证确实是kthread调用了complete(done);kthread_create才能返回否则__kthread_create_on_node会一直等待completion
测试代码如下
起了个定时器,定时器里面唤醒了一个内核线程.内核线程里面做了两个事情,一个是将comp_block设置为true,即跳过complete(done)另外一个是创建一个内核线程看看是否会阻塞
struct task_struct *task;
struct timer_list timer;
/* 通过该变量控制是否是否completion */
extern bool comp_block;int kill_thread(void* a)
{/* 不释放completion然后再看看kthread_create是否会阻塞 */comp_block true;printk(KERN_EMERG \r\n before create thread\n);kthread_create(test_thread, NULL, test_task);printk(KERN_EMERG \r\n after create thread\n);return;
}
void timer_work(unsigned long data)
{wake_up_process(task);return;
}static int smsc911x_init(struct net_device *dev)
{
...............................printk(KERN_EMERG \r\n softlockup simulate, in_interrupt %u in_softirq %u, NR_CPUS %d\n, in_interrupt(), in_softirq(), NR_CPUS);timer.expiresjiffiesmsecs_to_jiffies(20000);timer.functiontimer_work;init_timer(timer);add_timer(timer);printk(KERN_EMERG \r\n create thread\n); task kthread_create(kill_thread, NULL, kill_task);printk(KERN_EMERG \r\n create thread end\n);
....................................
}
bool comp_block false;
static int kthread(void *_create)
{
.............................../* OK, tell user were spawned, wait for stop or wakeup */__set_current_state(TASK_UNINTERRUPTIBLE);create-result current;if (false comp_block){complete(done);}schedule();
..........................................
}效果展示 可以看到并未打印kthread_create后面的log并且内核线程kill_task也是一直无法退出 如果定时器里面不设置comp_block的值即正常释放completionlog如下 内核线程退出kthread_stop
kthread_stop:只是告诉内核线程应该退出了但是要不要退出还需要看内核线程处理函数是否检查该消息并且检查到以后还必须主动退出。
1、设置内核线程为KTHREAD_SHOULD_STOP当内核线程的处理函数用kthread_should_stop检查标记时能感知到该事件如果内核线程一直不检查那么即使调用了kthread_stop也是没有用的
2、重新唤醒内核线程如何内核线程没有运行那么也是无法感知到这个事件的
3、等待completion释放
int kthread_stop(struct task_struct *k)
{struct kthread *kthread;int ret;trace_sched_kthread_stop(k);get_task_struct(k);kthread to_kthread(k);set_bit(KTHREAD_SHOULD_STOP, kthread-flags);kthread_unpark(k);wake_up_process(k);wait_for_completion(kthread-exited);ret k-exit_code;put_task_struct(k);trace_sched_kthread_stop_ret(ret);return ret;
} wait_for_completion(kthread-exited); 这个是在哪里释放的呢
exited其实就是vfork_done
static int kthread(void *_create)
{
........................................self-data data;init_completion(self-exited);init_completion(self-parked);/* 此时的current就已经是我们创建好的内核线程了 */current-vfork_done self-exited;..............................do_exit(ret);
} 那么vfork_done是在哪里释放的呢
do_exit--exit_mm--exit_mm_release--mm_release
static void mm_release(struct task_struct *tsk, struct mm_struct *mm)
{
.................................../** All done, finally we can wake up parent and return this mm to him.* Also kthread_stop() uses this completion for synchronization.*/if (tsk-vfork_done)complete_vfork_done(tsk);
}
