死锁问题----打印此刻系统中所有的task

本文主要是介绍死锁问题----打印此刻系统中所有的task，希望对大家解决编程问题提供一定的参考价值，需要的开发者们随着小编来一起学习吧！

一、task_struct的遍历

进程，线程和内核线程的基本属性都是由struct task_struct结构体定义的。
设备上运行的所有task都是通过双链表连成一串，其中第一个task就是init_task，最终又指向会init_task。因此可以通过首个task（init_task）通过双向链表（tasks）遍历所有task，最终回到init_task方式遍历所有的task。

首进程init_task在内核启动的时候静态赋值创建。(/init/init_task.c)

struct task_struct init_task
= {.state                	= 0,.stack                	= init_stack,.usage                	= REFCOUNT_INIT(2),.flags                	= PF_KTHREAD,.prio                	= MAX_PRIO - 20,.static_prio        		= MAX_PRIO - 20,.normal_prio        		= MAX_PRIO - 20,.policy                	= SCHED_NORMAL,.cpus_ptr        		= &init_task.cpus_mask,.cpus_mask        		= CPU_MASK_ALL,.nr_cpus_allowed			= NR_CPUS,.mm                		= NULL,.active_mm        		= &init_mm,.tasks					= LIST_HEAD_INIT(init_task.tasks),.......signal                	= &init_signals,.sighand        			= &init_sighand,.nsproxy        			= &init_nsproxy,.pending        			= {.list 	= LIST_HEAD_INIT(init_task.pending.list),.signal 	= {{0}}},.blocked        			= {{0}},.alloc_lock        		= __SPIN_LOCK_UNLOCKED(init_task.alloc_lock),.journal_info        	= NULL,INIT_CPU_TIMERS(init_task).pi_lock        			= __RAW_SPIN_LOCK_UNLOCKED(init_task.pi_lock),.timer_slack_ns 			= 50000, /* 50 usec default slack */.thread_pid        		= &init_struct_pid,.thread_group        	= LIST_HEAD_INIT(init_task.thread_group),.thread_node        		= LIST_HEAD_INIT(init_signals.thread_head),......
};
EXPORT_SYMBOL(init_task);

可以在编译生成的linux镜像中查找init_task符号表

nm vmlinux | grep init_task

然而一个进程中往往有很多线程，线程也与进程类似，通过双向链表串联，最终挂在进程task_struct下的thread_group
遍历系统中所有的进程和进程中所有的线程。

其中打印堆栈的方法：https://blog.csdn.net/sydyh43/article/details/119707079

二、遍历的实现

#define BKTRACE_DEPTH	30#define next_task(p)	list_entry_rcu((p)->tasks.next, struct task_struct, tasks)
#define next_thread(p)	list_entry_rcu((p)->thread_group.next, struct task_struct, thread_group)static void print_tasks_stack(void)
{struct task_struct *p = NULL, *tmp = NULL, *pt = NULL;unsigned long backtrace[BKTRACE_DEPTH];struct stack_trace trace;printk("dump stack....\n");rcu_read_lock();for (p = &init_task; (tmp = next_task(p)) != &init_task; ) {pt = p;do {if (pt->state == TASK_RUNNING) {printk("task name:%s\n", pt->comm);memset(backtrace, 0x00, sizeof(unsigned long) * BKTRACE_DEPTH);memset(&trace, 0x00, sizeof(struct stack_trace));trace.max_entries = BKTRACE_DEPTH;trace.entries = backtrace;save_stack_trace_tsk(pt, &trace);print_stack_trace(&trace, 0);			}if (pt->state & TASK_INTERRUPTIBLE) {printk("task name:%s\n", pt->comm);memset(backtrace, 0x00, sizeof(unsigned long) * BKTRACE_DEPTH);memset(&trace, 0x00, sizeof(struct stack_trace));trace.max_entries = BKTRACE_DEPTH;trace.entries = backtrace;save_stack_trace_tsk(pt, &trace);print_stack_trace(&trace, 0);}if (pt->state & TASK_UNINTERRUPTIBLE) {printk("task name:%s\n", pt->comm);memset(backtrace, 0x00, sizeof(unsigned long) * BKTRACE_DEPTH);memset(&trace, 0x00, sizeof(struct stack_trace));trace.max_entries = BKTRACE_DEPTH;trace.entries = backtrace;save_stack_trace_tsk(pt, &trace);print_stack_trace(&trace, 0);}}while((pt = next_thread(pt)) != p);p = tmp;}rcu_read_unlock();
}

遍历结果

发现个问题，创建线程时，printk("task name:%s\n", pt->comm);打印出来的线程名就是进程的名字，最终不好定位问题。

因此，在创建线程的时候最好指定线程名。创建线程名的方法。

#include <sys/prctl.h>static void *thread_fun0(void *arg)
{prctl(PR_SET_NAME, "thread_fun0");	while (1) {fun_b();sleep(5);}return NULL;
}

三、应用

1、模拟死锁的代码

static void fun_a(void)
{pthread_mutex_lock(&mtx0);sleep(2);printf("1%s\n", __func__);pthread_mutex_lock(&mtx1);printf("2%s\n", __func__);return;
}static void fun_b(void)
{pthread_mutex_lock(&mtx1);sleep(1);printf("1%s\n", __func__);	pthread_mutex_lock(&mtx0);printf("1%s\n", __func__);	return;
}static void *thread_fun0(void *arg)
{prctl(PR_SET_NAME, "thread_fun0");	while (1) {fun_a();sleep(5);}return NULL;
}static void *thread_fun1(void *arg)
{prctl(PR_SET_NAME, "thread_fun1");	while (1) {fun_b();sleep(7);}return NULL;
}

2、打印堆栈