1/* SPDX-License-Identifier: GPL-2.0 */ 2#ifndef _LINUX_PID_H 3#define _LINUX_PID_H 4 5#include <linux/pid_types.h> 6#include <linux/rculist.h> 7#include <linux/rcupdate.h> 8#include <linux/refcount.h> 9#include <linux/sched.h> 10#include <linux/wait.h> 11 12/* 13 * What is struct pid? 14 * 15 * A struct pid is the kernel's internal notion of a process identifier. 16 * It refers to individual tasks, process groups, and sessions. While 17 * there are processes attached to it the struct pid lives in a hash 18 * table, so it and then the processes that it refers to can be found 19 * quickly from the numeric pid value. The attached processes may be 20 * quickly accessed by following pointers from struct pid. 21 * 22 * Storing pid_t values in the kernel and referring to them later has a 23 * problem. The process originally with that pid may have exited and the 24 * pid allocator wrapped, and another process could have come along 25 * and been assigned that pid. 26 * 27 * Referring to user space processes by holding a reference to struct 28 * task_struct has a problem. When the user space process exits 29 * the now useless task_struct is still kept. A task_struct plus a 30 * stack consumes around 10K of low kernel memory. More precisely 31 * this is THREAD_SIZE + sizeof(struct task_struct). By comparison 32 * a struct pid is about 64 bytes. 33 * 34 * Holding a reference to struct pid solves both of these problems. 35 * It is small so holding a reference does not consume a lot of 36 * resources, and since a new struct pid is allocated when the numeric pid 37 * value is reused (when pids wrap around) we don't mistakenly refer to new 38 * processes. 39 */ 40 41 42/* 43 * struct upid is used to get the id of the struct pid, as it is 44 * seen in particular namespace. Later the struct pid is found with 45 * find_pid_ns() using the int nr and struct pid_namespace *ns. 46 */ 47 48#define RESERVED_PIDS 300 49 50struct upid { 51 int nr; 52 struct pid_namespace *ns; 53}; 54 55struct pid 56{ 57 refcount_t count; 58 unsigned int level; 59 spinlock_t lock; 60 struct dentry *stashed; 61 u64 ino; 62 /* lists of tasks that use this pid */ 63 struct hlist_head tasks[PIDTYPE_MAX]; 64 struct hlist_head inodes; 65 /* wait queue for pidfd notifications */ 66 wait_queue_head_t wait_pidfd; 67 struct rcu_head rcu; 68 struct upid numbers[]; 69}; 70 71extern struct pid init_struct_pid; 72 73struct file; 74 75struct pid *pidfd_pid(const struct file *file); 76struct pid *pidfd_get_pid(unsigned int fd, unsigned int *flags); 77struct task_struct *pidfd_get_task(int pidfd, unsigned int *flags); 78int pidfd_prepare(struct pid *pid, unsigned int flags, struct file **ret); 79void do_notify_pidfd(struct task_struct *task); 80 81static inline struct pid *get_pid(struct pid *pid) 82{ 83 if (pid) 84 refcount_inc(&pid->count); 85 return pid; 86} 87 88extern void put_pid(struct pid *pid); 89extern struct task_struct *pid_task(struct pid *pid, enum pid_type); 90static inline bool pid_has_task(struct pid *pid, enum pid_type type) 91{ 92 return !hlist_empty(&pid->tasks[type]); 93} 94extern struct task_struct *get_pid_task(struct pid *pid, enum pid_type); 95 96extern struct pid *get_task_pid(struct task_struct *task, enum pid_type type); 97 98/* 99 * these helpers must be called with the tasklist_lock write-held. 100 */ 101extern void attach_pid(struct task_struct *task, enum pid_type); 102extern void detach_pid(struct task_struct *task, enum pid_type); 103extern void change_pid(struct task_struct *task, enum pid_type, 104 struct pid *pid); 105extern void exchange_tids(struct task_struct *task, struct task_struct *old); 106extern void transfer_pid(struct task_struct *old, struct task_struct *new, 107 enum pid_type); 108 109extern int pid_max; 110extern int pid_max_min, pid_max_max; 111 112/* 113 * look up a PID in the hash table. Must be called with the tasklist_lock 114 * or rcu_read_lock() held. 115 * 116 * find_pid_ns() finds the pid in the namespace specified 117 * find_vpid() finds the pid by its virtual id, i.e. in the current namespace 118 * 119 * see also find_task_by_vpid() set in include/linux/sched.h 120 */ 121extern struct pid *find_pid_ns(int nr, struct pid_namespace *ns); 122extern struct pid *find_vpid(int nr); 123 124/* 125 * Lookup a PID in the hash table, and return with it's count elevated. 126 */ 127extern struct pid *find_get_pid(int nr); 128extern struct pid *find_ge_pid(int nr, struct pid_namespace *); 129 130extern struct pid *alloc_pid(struct pid_namespace *ns, pid_t *set_tid, 131 size_t set_tid_size); 132extern void free_pid(struct pid *pid); 133extern void disable_pid_allocation(struct pid_namespace *ns); 134 135/* 136 * ns_of_pid() returns the pid namespace in which the specified pid was 137 * allocated. 138 * 139 * NOTE: 140 * ns_of_pid() is expected to be called for a process (task) that has 141 * an attached 'struct pid' (see attach_pid(), detach_pid()) i.e @pid 142 * is expected to be non-NULL. If @pid is NULL, caller should handle 143 * the resulting NULL pid-ns. 144 */ 145static inline struct pid_namespace *ns_of_pid(struct pid *pid) 146{ 147 struct pid_namespace *ns = NULL; 148 if (pid) 149 ns = pid->numbers[pid->level].ns; 150 return ns; 151} 152 153/* 154 * is_child_reaper returns true if the pid is the init process 155 * of the current namespace. As this one could be checked before 156 * pid_ns->child_reaper is assigned in copy_process, we check 157 * with the pid number. 158 */ 159static inline bool is_child_reaper(struct pid *pid) 160{ 161 return pid->numbers[pid->level].nr == 1; 162} 163 164/* 165 * the helpers to get the pid's id seen from different namespaces 166 * 167 * pid_nr() : global id, i.e. the id seen from the init namespace; 168 * pid_vnr() : virtual id, i.e. the id seen from the pid namespace of 169 * current. 170 * pid_nr_ns() : id seen from the ns specified. 171 * 172 * see also task_xid_nr() etc in include/linux/sched.h 173 */ 174 175static inline pid_t pid_nr(struct pid *pid) 176{ 177 pid_t nr = 0; 178 if (pid) 179 nr = pid->numbers[0].nr; 180 return nr; 181} 182 183pid_t pid_nr_ns(struct pid *pid, struct pid_namespace *ns); 184pid_t pid_vnr(struct pid *pid); 185 186#define do_each_pid_task(pid, type, task) \ 187 do { \ 188 if ((pid) != NULL) \ 189 hlist_for_each_entry_rcu((task), \ 190 &(pid)->tasks[type], pid_links[type]) { 191 192 /* 193 * Both old and new leaders may be attached to 194 * the same pid in the middle of de_thread(). 195 */ 196#define while_each_pid_task(pid, type, task) \ 197 if (type == PIDTYPE_PID) \ 198 break; \ 199 } \ 200 } while (0) 201 202#define do_each_pid_thread(pid, type, task) \ 203 do_each_pid_task(pid, type, task) { \ 204 struct task_struct *tg___ = task; \ 205 for_each_thread(tg___, task) { 206 207#define while_each_pid_thread(pid, type, task) \ 208 } \ 209 task = tg___; \ 210 } while_each_pid_task(pid, type, task) 211 212static inline struct pid *task_pid(struct task_struct *task) 213{ 214 return task->thread_pid; 215} 216 217/* 218 * the helpers to get the task's different pids as they are seen 219 * from various namespaces 220 * 221 * task_xid_nr() : global id, i.e. the id seen from the init namespace; 222 * task_xid_vnr() : virtual id, i.e. the id seen from the pid namespace of 223 * current. 224 * task_xid_nr_ns() : id seen from the ns specified; 225 * 226 * see also pid_nr() etc in include/linux/pid.h 227 */ 228pid_t __task_pid_nr_ns(struct task_struct *task, enum pid_type type, struct pid_namespace *ns); 229 230static inline pid_t task_pid_nr(struct task_struct *tsk) 231{ 232 return tsk->pid; 233} 234 235static inline pid_t task_pid_nr_ns(struct task_struct *tsk, struct pid_namespace *ns) 236{ 237 return __task_pid_nr_ns(tsk, PIDTYPE_PID, ns); 238} 239 240static inline pid_t task_pid_vnr(struct task_struct *tsk) 241{ 242 return __task_pid_nr_ns(tsk, PIDTYPE_PID, NULL); 243} 244 245 246static inline pid_t task_tgid_nr(struct task_struct *tsk) 247{ 248 return tsk->tgid; 249} 250 251/** 252 * pid_alive - check that a task structure is not stale 253 * @p: Task structure to be checked. 254 * 255 * Test if a process is not yet dead (at most zombie state) 256 * If pid_alive fails, then pointers within the task structure 257 * can be stale and must not be dereferenced. 258 * 259 * Return: 1 if the process is alive. 0 otherwise. 260 */ 261static inline int pid_alive(const struct task_struct *p) 262{ 263 return p->thread_pid != NULL; 264} 265 266static inline pid_t task_pgrp_nr_ns(struct task_struct *tsk, struct pid_namespace *ns) 267{ 268 return __task_pid_nr_ns(tsk, PIDTYPE_PGID, ns); 269} 270 271static inline pid_t task_pgrp_vnr(struct task_struct *tsk) 272{ 273 return __task_pid_nr_ns(tsk, PIDTYPE_PGID, NULL); 274} 275 276 277static inline pid_t task_session_nr_ns(struct task_struct *tsk, struct pid_namespace *ns) 278{ 279 return __task_pid_nr_ns(tsk, PIDTYPE_SID, ns); 280} 281 282static inline pid_t task_session_vnr(struct task_struct *tsk) 283{ 284 return __task_pid_nr_ns(tsk, PIDTYPE_SID, NULL); 285} 286 287static inline pid_t task_tgid_nr_ns(struct task_struct *tsk, struct pid_namespace *ns) 288{ 289 return __task_pid_nr_ns(tsk, PIDTYPE_TGID, ns); 290} 291 292static inline pid_t task_tgid_vnr(struct task_struct *tsk) 293{ 294 return __task_pid_nr_ns(tsk, PIDTYPE_TGID, NULL); 295} 296 297static inline pid_t task_ppid_nr_ns(const struct task_struct *tsk, struct pid_namespace *ns) 298{ 299 pid_t pid = 0; 300 301 rcu_read_lock(); 302 if (pid_alive(tsk)) 303 pid = task_tgid_nr_ns(rcu_dereference(tsk->real_parent), ns); 304 rcu_read_unlock(); 305 306 return pid; 307} 308 309static inline pid_t task_ppid_nr(const struct task_struct *tsk) 310{ 311 return task_ppid_nr_ns(tsk, &init_pid_ns); 312} 313 314/* Obsolete, do not use: */ 315static inline pid_t task_pgrp_nr(struct task_struct *tsk) 316{ 317 return task_pgrp_nr_ns(tsk, &init_pid_ns); 318} 319 320/** 321 * is_global_init - check if a task structure is init. Since init 322 * is free to have sub-threads we need to check tgid. 323 * @tsk: Task structure to be checked. 324 * 325 * Check if a task structure is the first user space task the kernel created. 326 * 327 * Return: 1 if the task structure is init. 0 otherwise. 328 */ 329static inline int is_global_init(struct task_struct *tsk) 330{ 331 return task_tgid_nr(tsk) == 1; 332} 333 334#endif /* _LINUX_PID_H */ 335