Linux源码阅读笔记02-进程原理及系统调用

// 进程控制块
struct task_struct {
#ifdef CONFIG_THREAD_INFO_IN_TASK
  /*
   * For reasons of header soup (see current_thread_info()), this
   * must be the first element of task_struct.
   */
  struct thread_info    thread_info;
#endif
  /* -1 unrunnable, 0 runnable, >0 stopped: */
  volatile long     state; // 进程状态标志
  /*
   * This begins the randomizable portion of task_struct. Only
   * scheduling-critical items should be added above here.
   */
  randomized_struct_fields_start
  void        *stack; // 纸箱内核栈
  refcount_t      usage;
  /* Per task flags (PF_*), defined further below: */
  unsigned int      flags;
  unsigned int      ptrace;
#ifdef CONFIG_SMP
  struct llist_node   wake_entry;
  int       on_cpu;
#ifdef CONFIG_THREAD_INFO_IN_TASK
  /* Current CPU: */
  unsigned int      cpu;
#endif
  unsigned int      wakee_flips;
  unsigned long     wakee_flip_decay_ts;
  struct task_struct    *last_wakee;
  /*
   * recent_used_cpu is initially set as the last CPU used by a task
   * that wakes affine another task. Waker/wakee relationships can
   * push tasks around a CPU where each wakeup moves to the next one.
   * Tracking a recently used CPU allows a quick search for a recently
   * used CPU that may be idle.
   */
  int       recent_used_cpu;
  int       wake_cpu;
#endif
  int       on_rq;
  /*调度策略和优先级*/
  int       prio;
  int       static_prio;
  int       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
  struct sched_dl_entity    dl;
#ifdef CONFIG_UCLAMP_TASK
  /* Clamp values requested for a scheduling entity */
  struct uclamp_se    uclamp_req[UCLAMP_CNT];
  /* Effective clamp values used for a scheduling entity */
  struct uclamp_se    uclamp[UCLAMP_CNT];
#endif
#ifdef CONFIG_PREEMPT_NOTIFIERS
  /* List of struct preempt_notifier: */
  struct hlist_head   preempt_notifiers;
#endif
#ifdef CONFIG_BLK_DEV_IO_TRACE
  unsigned int      btrace_seq;
#endif
  unsigned int      policy;
  int       nr_cpus_allowed; // 
  const cpumask_t     *cpus_ptr; // 此成员允许进程在哪个cpu上运行
  cpumask_t     cpus_mask;
#ifdef CONFIG_PREEMPT_RCU
  int       rcu_read_lock_nesting;
  union rcu_special   rcu_read_unlock_special;
  struct list_head    rcu_node_entry;
  struct rcu_node     *rcu_blocked_node;
#endif /* #ifdef CONFIG_PREEMPT_RCU */
#ifdef CONFIG_TASKS_RCU
  unsigned long     rcu_tasks_nvcsw;
  u8        rcu_tasks_holdout;
  u8        rcu_tasks_idx;
  int       rcu_tasks_idle_cpu;
  struct list_head    rcu_tasks_holdout_list;
#endif /* #ifdef CONFIG_TASKS_RCU */
  struct sched_info   sched_info;
  struct list_head    tasks;
#ifdef CONFIG_SMP
  struct plist_node   pushable_tasks;
  struct rb_node      pushable_dl_tasks;
#endif
  // 指向内存描述符。进程：mm和active_mm指向同一个内存描述符。内核线程：mm是空指针
  // 当内核线程运行时，active_mm指向从进程借用内存描述符
  struct mm_struct    *mm;
  struct mm_struct    *active_mm; 
  /* Per-thread vma caching: */
  struct vmacache     vmacache;
#ifdef SPLIT_RSS_COUNTING
  struct task_rss_stat    rss_stat;
#endif
  int       exit_state;
  int       exit_code;
  int       exit_signal;
  /* The signal sent when the parent dies: */
  int       pdeath_signal;
  /* JOBCTL_*, siglock protected: */
  unsigned long     jobctl;
  /* Used for emulating ABI behavior of previous Linux versions: */
  unsigned int      personality;
  /* Scheduler bits, serialized by scheduler locks: */
  unsigned      sched_reset_on_fork:1;
  unsigned      sched_contributes_to_load:1;
  unsigned      sched_migrated:1;
  unsigned      sched_remote_wakeup:1;
#ifdef CONFIG_PSI
  unsigned      sched_psi_wake_requeue:1;
#endif
  /* Force alignment to the next boundary: */
  unsigned      :0;
  /* Unserialized, strictly 'current' */
  /* Bit to tell LSMs we're in execve(): */
  unsigned      in_execve:1;
  unsigned      in_iowait:1;
#ifndef TIF_RESTORE_SIGMASK
  unsigned      restore_sigmask:1;
#endif
#ifdef CONFIG_MEMCG
  unsigned      in_user_fault:1;
#endif
#ifdef CONFIG_COMPAT_BRK
  unsigned      brk_randomized:1;
#endif
#ifdef CONFIG_CGROUPS
  /* disallow userland-initiated cgroup migration */
  unsigned      no_cgroup_migration:1;
  /* task is frozen/stopped (used by the cgroup freezer) */
  unsigned      frozen:1;
#endif
#ifdef CONFIG_BLK_CGROUP
  /* to be used once the psi infrastructure lands upstream. */
  unsigned      use_memdelay:1;
#endif
  unsigned long     atomic_flags; /* Flags requiring atomic access. */
  struct restart_block    restart_block;
  pid_t       pid; // 全局进程号
  pid_t       tgid; // 全局线程组的标识符
#ifdef CONFIG_STACKPROTECTOR
  /* Canary value for the -fstack-protector GCC feature: */
  unsigned long     stack_canary;
#endif
  /*
   * Pointers to the (original) parent process, youngest child, younger sibling,
   * older sibling, respectively.  (p->father can be replaced with
   * p->real_parent->pid)
   */
  /* Real parent process: */
  struct task_struct __rcu  *real_parent; // 指向真实父进程
  /* Recipient of SIGCHLD, wait4() reports: */
  struct task_struct __rcu  *parent; // 指向父进程 如果使用系统调用跟踪进程，这个是跟踪进程，否则和real_parent是相同的
  /*
   * Children/sibling form the list of natural children:
   */
  struct list_head    children;
  struct list_head    sibling;
  struct task_struct    *group_leader; // 指向线程组的组长
  /*
   * 'ptraced' is the list of tasks this task is using ptrace() on.
   *
   * This includes both natural children and PTRACE_ATTACH targets.
   * 'ptrace_entry' is this task's link on the p->parent->ptraced list.
   */
  struct list_head    ptraced;
  struct list_head    ptrace_entry;
  /* PID/PID hash table linkage. */
  struct pid      *thread_pid;
  struct hlist_node   pid_links[PIDTYPE_MAX]; // 进程号，进程组标识符和会话标识符
  struct list_head    thread_group;
  struct list_head    thread_node;
  struct completion   *vfork_done;
  /* CLONE_CHILD_SETTID: */
  int __user      *set_child_tid;
  /* CLONE_CHILD_CLEARTID: */
  int __user      *clear_child_tid;
  u64       utime;
  u64       stime;
#ifdef CONFIG_ARCH_HAS_SCALED_CPUTIME
  u64       utimescaled;
  u64       stimescaled;
#endif
  u64       gtime;
  struct prev_cputime   prev_cputime;
#ifdef CONFIG_VIRT_CPU_ACCOUNTING_GEN
  struct vtime      vtime;
#endif
#ifdef CONFIG_NO_HZ_FULL
  atomic_t      tick_dep_mask;
#endif
  /* Context switch counts: */
  unsigned long     nvcsw;
  unsigned long     nivcsw;
  /* Monotonic time in nsecs: */
  u64       start_time;
  /* Boot based time in nsecs: */
  u64       start_boottime;
  /* MM fault and swap info: this can arguably be seen as either mm-specific or thread-specific: */
  unsigned long     min_flt;
  unsigned long     maj_flt;
  /* Empty if CONFIG_POSIX_CPUTIMERS=n */
  struct posix_cputimers    posix_cputimers;
  /* Process credentials: */
  /* Tracer's credentials at attach: */
  const struct cred __rcu   *ptracer_cred;
  /* Objective and real subjective task credentials (COW): */
  const struct cred __rcu   *real_cred; // 此成员指向主体和真实客体证书
  /* Effective (overridable) subjective task credentials (COW): */
  const struct cred __rcu   *cred; // 指向有效证书 但是可以临时改变
#ifdef CONFIG_KEYS
  /* Cached requested key. */
  struct key      *cached_requested_key;
#endif
  /*
   * executable name, excluding path.
   *
   * - normally initialized setup_new_exec()
   * - access it with [gs]et_task_comm()
   * - lock it with task_lock()
   */
  char        comm[TASK_COMM_LEN]; // 进程名称
  struct nameidata    *nameidata;
  // 下面这两个成员用于UNIX系统，型号量和共享内存
#ifdef CONFIG_SYSVIPC
  struct sysv_sem     sysvsem;
  struct sysv_shm     sysvshm;
#endif
#ifdef CONFIG_DETECT_HUNG_TASK
  unsigned long     last_switch_count;
  unsigned long     last_switch_time;
#endif
  /* Filesystem information: */
  struct fs_struct    *fs; // 文件系统信息，主要是进程根目录和当前工作目录
  /* Open file information: */
  struct files_struct   *files; // 打开文件表
  /* Namespaces: */
  struct nsproxy      *nsproxy; // 命名空间
  // 下面这快成员用于信号处理
  /* Signal handlers: */
  struct signal_struct    *signal;
  struct sighand_struct __rcu   *sighand;
  sigset_t      blocked;
  sigset_t      real_blocked;
  /* Restored if set_restore_sigmask() was used: */
  sigset_t      saved_sigmask;
  struct sigpending   pending;
  unsigned long     sas_ss_sp;
  size_t        sas_ss_size;
  unsigned int      sas_ss_flags;
  struct callback_head    *task_works;
#ifdef CONFIG_AUDIT
#ifdef CONFIG_AUDITSYSCALL
  struct audit_context    *audit_context;
#endif
  kuid_t        loginuid;
  unsigned int      sessionid;
#endif
  struct seccomp      seccomp;
  /* Thread group tracking: */
  u64       parent_exec_id;
  u64       self_exec_id;
  /* Protection against (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;
  struct wake_q_node    wake_q;
#ifdef CONFIG_RT_MUTEXES
  /* PI waiters blocked on a rt_mutex held by this task: */
  struct rb_root_cached   pi_waiters;
  /* Updated under owner's pi_lock and rq lock */
  struct task_struct    *pi_top_task;
  /* 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_DEBUG_ATOMIC_SLEEP
  int       non_block_count;
#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];
#endif
#ifdef CONFIG_UBSAN
  unsigned int      in_ubsan;
#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;
#ifdef CONFIG_COMPACTION
  struct capture_control    *capture_control;
#endif
  /* Ptrace state: */
  unsigned long     ptrace_message;
  kernel_siginfo_t    *last_siginfo;
  struct task_io_accounting ioac;
#ifdef CONFIG_PSI
  /* Pressure stall state */
  unsigned int      psi_flags;
#endif
#ifdef CONFIG_TASK_XACCT
  /* Accumulated RSS usage: */
  u64       acct_rss_mem1;
  /* Accumulated virtual memory usage: */
  u64       acct_vm_mem1;
  /* stime + utime since last update: */
  u64       acct_timexpd;
#endif
#ifdef CONFIG_CPUSETS
  /* Protected by ->alloc_lock: */
  nodemask_t      mems_allowed;
  /* Seqence number to catch updates: */
  seqcount_t      mems_allowed_seq;
  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_X86_CPU_RESCTRL
  u32       closid;
  u32       rmid;
#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;
  struct mutex      futex_exit_mutex;
  unsigned int      futex_state;
#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_DEBUG_PREEMPT
  unsigned long     preempt_disable_ip;
#endif
#ifdef CONFIG_NUMA
  /* Protected by alloc_lock: */
  struct mempolicy    *mempolicy;
  short       il_prev;
  short       pref_node_fork;
#endif
#ifdef CONFIG_NUMA_BALANCING
  int       numa_scan_seq;
  unsigned int      numa_scan_period;
  unsigned int      numa_scan_period_max;
  int       numa_preferred_nid;
  unsigned long     numa_migrate_retry;
  /* Migration stamp: */
  u64       node_stamp;
  u64       last_task_numa_placement;
  u64       last_sum_exec_runtime;
  struct callback_head    numa_work;
  /*
   * This pointer is only modified for current in syscall and
   * pagefault context (and for tasks being destroyed), so it can be read
   * from any of the following contexts:
   *  - RCU read-side critical section
   *  - current->numa_group from everywhere
   *  - task's runqueue locked, task not running
   */
  struct numa_group __rcu   *numa_group;
  /*
   * numa_faults is an array split into four regions:
   * faults_memory, faults_cpu, faults_memory_buffer, faults_cpu_buffer
   * in this precise order.
   *
   * faults_memory: Exponential decaying average of faults on a per-node
   * basis. Scheduling placement decisions are made based on these
   * counts. The values remain static for the duration of a PTE scan.
   * faults_cpu: Track the nodes the process was running on when a NUMA
   * hinting fault was incurred.
   * faults_memory_buffer and faults_cpu_buffer: Record faults per node
   * during the current scan window. When the scan completes, the counts
   * in faults_memory and faults_cpu decay and these values are copied.
   */
  unsigned long     *numa_faults;
  unsigned long     total_numa_faults;
  /*
   * numa_faults_locality tracks if faults recorded during the last
   * scan window were remote/local or failed to migrate. The task scan
   * period is adapted based on the locality of the faults with different
   * weights depending on whether they were shared or private faults
   */
  unsigned long     numa_faults_locality[3];
  unsigned long     numa_pages_migrated;
#endif /* CONFIG_NUMA_BALANCING */
#ifdef CONFIG_RSEQ
  struct rseq __user *rseq;
  u32 rseq_sig;
  /*
   * RmW on rseq_event_mask must be performed atomically
   * with respect to preemption.
   */
  unsigned long rseq_event_mask;
#endif
  struct tlbflush_unmap_batch tlb_ubc;
  union {
    refcount_t    rcu_users;
    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;
  unsigned int      fail_nth;
#endif
  /*
   * When (nr_dirtied >= nr_dirtied_pause), it's time to call
   * balance_dirty_pages() for a dirty throttling pause:
   */
  int       nr_dirtied;
  int       nr_dirtied_pause;
  /* Start of a write-and-pause period: */
  unsigned long     dirty_paused_when;
#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.
   */
  u64       timer_slack_ns;
  u64       default_timer_slack_ns;
#ifdef CONFIG_KASAN
  unsigned int      kasan_depth;
#endif
#ifdef CONFIG_FUNCTION_GRAPH_TRACER
  /* Index of current stored address in ret_stack: */
  int       curr_ret_stack;
  int       curr_ret_depth;
  /* Stack of return addresses for return function tracing: */
  struct ftrace_ret_stack   *ret_stack;
  /* Timestamp 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 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_KCOV
  /* See kernel/kcov.c for more details. */
  /* Coverage collection mode enabled for this task (0 if disabled): */
  unsigned int      kcov_mode;
  /* Size of the kcov_area: */
  unsigned int      kcov_size;
  /* Buffer for coverage collection: */
  void        *kcov_area;
  /* KCOV descriptor wired with this task or NULL: */
  struct kcov     *kcov;
  /* KCOV common handle for remote coverage collection: */
  u64       kcov_handle;
  /* KCOV sequence number: */
  int       kcov_sequence;
#endif
#ifdef CONFIG_MEMCG
  struct mem_cgroup   *memcg_in_oom;
  gfp_t       memcg_oom_gfp_mask;
  int       memcg_oom_order;
  /* Number of pages to reclaim on returning to userland: */
  unsigned int      memcg_nr_pages_over_high;
  /* Used by memcontrol for targeted memcg charge: */
  struct mem_cgroup   *active_memcg;
#endif
#ifdef CONFIG_BLK_CGROUP
  struct request_queue    *throttle_queue;
#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
#ifdef CONFIG_DEBUG_ATOMIC_SLEEP
  unsigned long     task_state_change;
#endif
  int       pagefault_disabled;
#ifdef CONFIG_MMU
  struct task_struct    *oom_reaper_list;
#endif
#ifdef CONFIG_VMAP_STACK
  struct vm_struct    *stack_vm_area;
#endif
#ifdef CONFIG_THREAD_INFO_IN_TASK
  /* A live task holds one reference: */
  refcount_t      stack_refcount;
#endif
#ifdef CONFIG_LIVEPATCH
  int patch_state;
#endif
#ifdef CONFIG_SECURITY
  /* Used by LSM modules for access restriction: */
  void        *security;
#endif
#ifdef CONFIG_GCC_PLUGIN_STACKLEAK
  unsigned long     lowest_stack;
  unsigned long     prev_lowest_stack;
#endif
  /*
   * New fields for task_struct should be added above here, so that
   * they are included in the randomized portion of task_struct.
   */
  randomized_struct_fields_end
  /* CPU-specific state of this task: */
  struct thread_struct    thread;
  /*
   * WARNING: on x86, 'thread_struct' contains a variable-sized
   * structure.  It *MUST* be at the end of 'task_struct'.
   *
   * Do not put anything below here!
   */
};