linux 内核介绍2 进程管理

进程管理

进程管理包括创建进程、管理进程、及删除进程。

1、进程

进程是程序执行时的一个实体。程序包括指令和数据，而进程包括程序计数器和全部CPU寄存器的值。进程中的堆栈中存储着一些数据，如子程序的参数，返回地址及变量之类的临时数据。当前的执行程序（进程）包含着当前处理器中的活动状态。

Linux是一个多处理操作系统，进程拥有独立的权限和单一职责。如果系统中某个进程发生崩溃，它不会影响到另外的进程。每个进程都运行在其各自独立的虚拟地址空间中，只有通过核心控制下可靠的进程通信机制，它们之间才能发生通信。

进程间通信包括管道、信号量、信号、消息队列。

从内核的观点来看，进程的目的就是担当分配系统资源的实体。

2、进程描述符

内核对进程的优先级、进程的状态、地址空间等采用经常描述符表示。在Linux内核中，进程用相当大的一个称为task_struct的结构表示。

结构体定义路径：linux-3.9.6/include/linux/sched.h

     如下所示：

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_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;
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_statrss_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 */
/* ??? */
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;


#ifdef CONFIG_GENERIC_HARDIRQS
/* IRQ handler threads */
unsigned irq_thread:1;
#endif


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 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
cputime_t prev_utime, prev_stime;
#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) */
struct cred *replacement_session_keyring; /* for KEYCTL_SESSION_TO_PARENT */


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 audit_context *audit_context;
#ifdef CONFIG_AUDITSYSCALL
uid_t loginuid;
unsigned int sessionid;
#endif
seccomp_t 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
struct rcu_head rcu;


/*
* cache last used pipe for splice
*/
struct pipe_inode_info *splice_pipe;
#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;


struct list_head*scm_work_list;
#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_CGROUP_MEM_RES_CTLR /* 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;
#endif
#ifdef CONFIG_HAVE_HW_BREAKPOINT
atomic_t ptrace_bp_refcnt;
#endif
};