进程描述符和任务结构

痛定思痛。 2022-05-21 00:20 140阅读 0赞

### 进程描述符和任务结构 ###

*  进程的列表存放在任务队列中，任务队列是一个双向的循环链表。
 *  链表中的每一项都是类型为task\_struct的结构，称为进程描述符。
 *  进程描述符中包含有进程运行的所有信息，比如状态，标识符，优先级等等具体的介绍见[https://blog.csdn.net/bit\_clearoff/article/details/54292300][https_blog.csdn.net_bit_clearoff_article_details_54292300]

<table> 
 <thead> 
  <tr> 
   <th>描述信息</th> 
   <th>说明</th> 
  </tr> 
 </thead> 
 <tbody> 
  <tr> 
   <td>标识符</td> 
   <td>与进程相关的唯一标识符，用来区别正在执行的进程和其他进程。</td> 
  </tr> 
  <tr> 
   <td>状态</td> 
   <td>描述进程的状态，因为进程有挂起，阻塞，运行等好几个状态，所以都有个标识符来记录进程的执行状态。</td> 
  </tr> 
  <tr> 
   <td>优先级</td> 
   <td>如果有好几个进程正在执行，就涉及到进程被执行的先后顺序的问题，这和进程优先级这个标识符有关。</td> 
  </tr> 
  <tr> 
   <td>程序计数器</td> 
   <td>程序中即将被执行的下一条指令的地址。</td> 
  </tr> 
  <tr> 
   <td>内存指针</td> 
   <td>程序代码和进程相关数据的指针。</td> 
  </tr> 
  <tr> 
   <td>上下文数据</td> 
   <td>进程执行时处理器的寄存器中的数据。</td> 
  </tr> 
  <tr> 
   <td>I/O状态信息</td> 
   <td>包括显示的I/O请求，分配给进程的I/O设备和被进程使用的文件列表等。</td> 
  </tr> 
  <tr> 
   <td>记账信息</td> 
   <td>包括处理器的时间总和，记账号等等。</td> 
  </tr> 
 </tbody> 
</table>

struct task_struct {
        volatile long state;    /* -1 unrunnable, 0 runnable, >0 stopped */
        void *stack;
        atomic_t usage;
        unsigned int flags; /* per process flags, defined below */
        unsigned int ptrace;
    
    #ifdef CONFIG_SMP
        struct llist_node wake_entry;
        int on_cpu;
    #endif
        int on_rq;
    
        int prio, static_prio, normal_prio;
        unsigned int rt_priority;
        const struct sched_class *sched_class;
        struct sched_entity se;
        struct sched_rt_entity rt;
    #ifdef CONFIG_CGROUP_SCHED
        struct task_group *sched_task_group;
    #endif
    
    #ifdef CONFIG_PREEMPT_NOTIFIERS
        /* list of struct preempt_notifier: */
        struct hlist_head preempt_notifiers;
    #endif
    
        /* * fpu_counter contains the number of consecutive context switches * that the FPU is used. If this is over a threshold, the lazy fpu * saving becomes unlazy to save the trap. This is an unsigned char * so that after 256 times the counter wraps and the behavior turns * lazy again; this to deal with bursty apps that only use FPU for * a short time */
        unsigned char fpu_counter;
    #ifdef CONFIG_BLK_DEV_IO_TRACE
        unsigned int btrace_seq;
    #endif
    
        unsigned int policy;
        int nr_cpus_allowed;
        cpumask_t cpus_allowed;
    
    #ifdef CONFIG_PREEMPT_RCU
        int rcu_read_lock_nesting;
        char rcu_read_unlock_special;
        struct list_head rcu_node_entry;
    #endif /* #ifdef CONFIG_PREEMPT_RCU */
    #ifdef CONFIG_TREE_PREEMPT_RCU
        struct rcu_node *rcu_blocked_node;
    #endif /* #ifdef CONFIG_TREE_PREEMPT_RCU */
    #ifdef CONFIG_RCU_BOOST
        struct rt_mutex *rcu_boost_mutex;
    #endif /* #ifdef CONFIG_RCU_BOOST */
    
    #if defined(CONFIG_SCHEDSTATS) || defined(CONFIG_TASK_DELAY_ACCT)
        struct sched_info sched_info;
    #endif
    
        struct list_head tasks;
    #ifdef CONFIG_SMP
        struct plist_node pushable_tasks;
    #endif
    
        struct mm_struct *mm, *active_mm;
    #ifdef CONFIG_COMPAT_BRK
        unsigned brk_randomized:1;
    #endif
    #if defined(SPLIT_RSS_COUNTING)
        struct task_rss_stat    rss_stat;
    #endif
    /* task state */
        int exit_state;
        int exit_code, exit_signal;
        int pdeath_signal;  /* The signal sent when the parent dies */
        unsigned int jobctl;    /* JOBCTL_*, siglock protected */
    
        /* Used for emulating ABI behavior of previous Linux versions */
        unsigned int personality;
    
        unsigned did_exec:1;
        unsigned in_execve:1;   /* Tell the LSMs that the process is doing an * execve */
        unsigned in_iowait:1;
    
        /* Revert to default priority/policy when forking */
        unsigned sched_reset_on_fork:1;
        unsigned sched_contributes_to_load:1;
    
        unsigned long atomic_flags; /* Flags needing atomic access. */
    
        pid_t pid;
        pid_t tgid;
    
    #ifdef CONFIG_CC_STACKPROTECTOR
        /* Canary value for the -fstack-protector gcc feature */
        unsigned long stack_canary;
    #endif
        /* * pointers to (original) parent process, youngest child, younger sibling, * older sibling, respectively. (p->father can be replaced with * p->real_parent->pid) */
        struct task_struct __rcu *real_parent; /* real parent process */
        struct task_struct __rcu *parent; /* recipient of SIGCHLD, wait4() reports */
        /* * children/sibling forms the list of my natural children */
        struct list_head children;  /* list of my children */
        struct list_head sibling;   /* linkage in my parent's children list */
        struct task_struct *group_leader;   /* threadgroup leader */
    
        /* * ptraced is the list of tasks this task is using ptrace on. * This includes both natural children and PTRACE_ATTACH targets. * p->ptrace_entry is p's link on the p->parent->ptraced list. */
        struct list_head ptraced;
        struct list_head ptrace_entry;
    
        /* PID/PID hash table linkage. */
        struct pid_link pids[PIDTYPE_MAX];
        struct list_head thread_group;
        struct list_head thread_node;
    
        struct completion *vfork_done;      /* for vfork() */
        int __user *set_child_tid;      /* CLONE_CHILD_SETTID */
        int __user *clear_child_tid;        /* CLONE_CHILD_CLEARTID */
    
        cputime_t utime, stime, utimescaled, stimescaled;
        cputime_t gtime;
    #ifndef CONFIG_VIRT_CPU_ACCOUNTING_NATIVE
        struct cputime prev_cputime;
    #endif
    #ifdef CONFIG_VIRT_CPU_ACCOUNTING_GEN
        seqlock_t vtime_seqlock;
        unsigned long long vtime_snap;
        enum {
           VTIME_SLEEPING = 0,
            VTIME_USER,
            VTIME_SYS,
        } vtime_snap_whence;
    #endif
        unsigned long nvcsw, nivcsw; /* context switch counts */
        struct timespec start_time;         /* monotonic time */
        struct timespec real_start_time;    /* boot based time */
    /* mm fault and swap info: this can arguably be seen as either mm-specific or thread-specific */
        unsigned long min_flt, maj_flt;
    
        struct task_cputime cputime_expires;
        struct list_head cpu_timers[3];
    
    /* process credentials */
        const struct cred __rcu *real_cred; /* objective and real subjective task * credentials (COW) */
        const struct cred __rcu *cred;  /* effective (overridable) subjective task * credentials (COW) */
        char comm[TASK_COMM_LEN]; /* executable name excluding path - access with [gs]et_task_comm (which lock it with task_lock()) - initialized normally by setup_new_exec */
    /* file system info */
        int link_count, total_link_count;
    #ifdef CONFIG_SYSVIPC
    /* ipc stuff */
        struct sysv_sem sysvsem;
    #endif
    #ifdef CONFIG_DETECT_HUNG_TASK
    /* hung task detection */
        unsigned long last_switch_count;
    #endif
    /* CPU-specific state of this task */
        struct thread_struct thread;
    /* filesystem information */
        struct fs_struct *fs;
    /* open file information */
        struct files_struct *files;
    /* namespaces */
        struct nsproxy *nsproxy;
    /* signal handlers */
        struct signal_struct *signal;
        struct sighand_struct *sighand;
    
        sigset_t blocked, real_blocked;
        sigset_t saved_sigmask; /* restored if set_restore_sigmask() was used */
        struct sigpending pending;
    
        unsigned long sas_ss_sp;
        size_t sas_ss_size;
        int (*notifier)(void *priv);
        void *notifier_data;
        sigset_t *notifier_mask;
        struct callback_head *task_works;
    
        struct audit_context *audit_context;
    #ifdef CONFIG_AUDITSYSCALL
        kuid_t loginuid;
        unsigned int sessionid;
    #endif
        struct seccomp seccomp;
    
    /* Thread group tracking */
        u32 parent_exec_id;
        u32 self_exec_id;
    /* Protection of (de-)allocation: mm, files, fs, tty, keyrings, mems_allowed, * mempolicy */
        spinlock_t alloc_lock;
    
        /* Protection of the PI data structures: */
        raw_spinlock_t pi_lock;
    
    #ifdef CONFIG_RT_MUTEXES
        /* PI waiters blocked on a rt_mutex held by this task */
        struct plist_head pi_waiters;
        /* Deadlock detection and priority inheritance handling */
        struct rt_mutex_waiter *pi_blocked_on;
    #endif
    
    #ifdef CONFIG_DEBUG_MUTEXES
        /* mutex deadlock detection */
        struct mutex_waiter *blocked_on;
    #endif
    #ifdef CONFIG_TRACE_IRQFLAGS
        unsigned int irq_events;
        unsigned long hardirq_enable_ip;
        unsigned long hardirq_disable_ip;
        unsigned int hardirq_enable_event;
        unsigned int hardirq_disable_event;
        int hardirqs_enabled;
        int hardirq_context;
        unsigned long softirq_disable_ip;
        unsigned long softirq_enable_ip;
        unsigned int softirq_disable_event;
        unsigned int softirq_enable_event;
        int softirqs_enabled;
        int softirq_context;
    #endif
    #ifdef CONFIG_LOCKDEP
    # define MAX_LOCK_DEPTH 48UL
        u64 curr_chain_key;
        int lockdep_depth;
        unsigned int lockdep_recursion;
        struct held_lock held_locks[MAX_LOCK_DEPTH];
        gfp_t lockdep_reclaim_gfp;
    #endif
    
    /* journalling filesystem info */
        void *journal_info;
    
    /* stacked block device info */
        struct bio_list *bio_list;
    
    #ifdef CONFIG_BLOCK
    /* stack plugging */
        struct blk_plug *plug;
    #endif
    
    /* VM state */
        struct reclaim_state *reclaim_state;
    
        struct backing_dev_info *backing_dev_info;
    
        struct io_context *io_context;
    
        unsigned long ptrace_message;
        siginfo_t *last_siginfo; /* For ptrace use. */
        struct task_io_accounting ioac;
    #if defined(CONFIG_TASK_XACCT)
        u64 acct_rss_mem1;  /* accumulated rss usage */
        u64 acct_vm_mem1;   /* accumulated virtual memory usage */
        cputime_t acct_timexpd; /* stime + utime since last update */
    #endif
    #ifdef CONFIG_CPUSETS
        nodemask_t mems_allowed;    /* Protected by alloc_lock */
        seqcount_t mems_allowed_seq;    /* Seqence no to catch updates */
        int cpuset_mem_spread_rotor;
        int cpuset_slab_spread_rotor;
    #endif
    #ifdef CONFIG_CGROUPS
        /* Control Group info protected by css_set_lock */
        struct css_set __rcu *cgroups;
        /* cg_list protected by css_set_lock and tsk->alloc_lock */
        struct list_head cg_list;
    #endif
    #ifdef CONFIG_FUTEX
        struct robust_list_head __user *robust_list;
    #ifdef CONFIG_COMPAT
        struct compat_robust_list_head __user *compat_robust_list;
    #endif
        struct list_head pi_state_list;
        struct futex_pi_state *pi_state_cache;
    #endif
    #ifdef CONFIG_PERF_EVENTS
        struct perf_event_context *perf_event_ctxp[perf_nr_task_contexts];
        struct mutex perf_event_mutex;
        struct list_head perf_event_list;
    #endif
    #ifdef CONFIG_NUMA
        struct mempolicy *mempolicy;    /* Protected by alloc_lock */
        short il_next;
        short pref_node_fork;
    #endif
    #ifdef CONFIG_NUMA_BALANCING
        int numa_scan_seq;
        int numa_migrate_seq;
        unsigned int numa_scan_period;
        u64 node_stamp;         /* migration stamp */
        struct callback_head numa_work;
    #endif /* CONFIG_NUMA_BALANCING */
    
        struct rcu_head rcu;
    
        /* * cache last used pipe for splice */
        struct pipe_inode_info *splice_pipe;
    
        struct page_frag task_frag;
    
    #ifdef CONFIG_TASK_DELAY_ACCT
        struct task_delay_info *delays;
    #endif
    #ifdef CONFIG_FAULT_INJECTION
        int make_it_fail;
    #endif
        /* * when (nr_dirtied >= nr_dirtied_pause), it's time to call * balance_dirty_pages() for some dirty throttling pause */
        int nr_dirtied;
        int nr_dirtied_pause;
        unsigned long dirty_paused_when; /* start of a write-and-pause period */
    
    #ifdef CONFIG_LATENCYTOP
        int latency_record_count;
        struct latency_record latency_record[LT_SAVECOUNT];
    #endif
        /* * time slack values; these are used to round up poll() and * select() etc timeout values. These are in nanoseconds. */
        unsigned long timer_slack_ns;
        unsigned long default_timer_slack_ns;
    
    #ifdef CONFIG_FUNCTION_GRAPH_TRACER
        /* Index of current stored address in ret_stack */
        int curr_ret_stack;
        /* Stack of return addresses for return function tracing */
        struct ftrace_ret_stack *ret_stack;
        /* time stamp for last schedule */
        unsigned long long ftrace_timestamp;
        /* * Number of functions that haven't been traced * because of depth overrun. */
        atomic_t trace_overrun;
        /* Pause for the tracing */
        atomic_t tracing_graph_pause;
    #endif
    #ifdef CONFIG_TRACING
        /* state flags for use by tracers */
        unsigned long trace;
        /* bitmask and counter of trace recursion */
        unsigned long trace_recursion;
    #endif /* CONFIG_TRACING */
    #ifdef CONFIG_MEMCG /* memcg uses this to do batch job */
        struct memcg_batch_info {
            int do_batch;   /* incremented when batch uncharge started */
            struct mem_cgroup *memcg; /* target memcg of uncharge */
            unsigned long nr_pages; /* uncharged usage */
            unsigned long memsw_nr_pages; /* uncharged mem+swap usage */
        } memcg_batch;
        unsigned int memcg_kmem_skip_account;
    #endif
    #ifdef CONFIG_HAVE_HW_BREAKPOINT
        atomic_t ptrace_bp_refcnt;
    #endif
    #ifdef CONFIG_UPROBES
        struct uprobe_task *utask;
    #endif
    #if defined(CONFIG_BCACHE) || defined(CONFIG_BCACHE_MODULE)
        unsigned int    sequential_io;
        unsigned int    sequential_io_avg;
    #endif
    };

##### 进程描述符的存放 #####

*  内核通过一个唯一的进程标识值或者PID来标识每个进程。PID的最大默认设置为32768
 *  内核中访问进程任务通常是获取指向task\_struct的指针，内核中大部分处理进程的代码都是直接通过访问task\_struct进行的。

##### 进程的状态 #####

#define TASK_RUNNING 0 //表示进程要么正在执行，要么正要准备执行。
    #define TASK_INTERRUPTIBLE 1 //表示进程被阻塞（睡眠），直到某个条件变为真。条件一旦达成，进程的状态就被设置为TASK_RUNNING。
    #define TASK_UNINTERRUPTIBLE 2 //意义与TASK_INTERRUPTIBLE类似，除了不能通过接受一个信号来唤醒以外。
    #define __TASK_STOPPED 4 //表示进程被停止执行。
    #define __TASK_TRACED 8 //表示进程被debugger等进程监视。(被另一个进程跟踪)

*  通过ps命令查看到的那些被标记为D的又不能被杀死的就是TASK\_UNINTERRUPTIBLE，所以无法给他发送SIGKILL信号。

##### 对当前进程的状态进行设置 #####

*  内核经常需要调整某个进程的状态.这时最好使用set\_task\_state(task,state)函数:

set_task_state(task, state); /.将任务task的状态设置为state./

*  该函数将指定的进程设置为指定的状态。必要的时候，它会设置内存屏障来强制其他处理器作重新排序。(一般只有在SMP系统中有此必要。)否则，它等价于:  
    task一>state=state;
 *  set\_current\_state(state)和set\_task\_state(current, state)含义是等同的。参见

##### 进程上下文含义 #####

*  一般程序在用户空间执行，当一个程序调用了系统调用或者触发了某个异常，程序就会陷入内核空间。这个时候称为内核“代表进程执行”并处于进程上下文。在此上下文中除非有更高优先级的进程需要执行并由调度器做了相应调整，否则在内核退出的时候程序恢复在用户空间的工作并继续执行。

[https_blog.csdn.net_bit_clearoff_article_details_54292300]: https://blog.csdn.net/bit_clearoff/article/details/54292300