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 struct upid { 49 int nr; 50 struct pid_namespace *ns; 51 }; 52 53 struct pid 54 { 55 refcount_t count; 56 unsigned int level; 57 spinlock_t lock; 58 /* lists of tasks that use this pid */ 59 struct hlist_head tasks[PIDTYPE_MAX]; 60 struct hlist_head inodes; 61 /* wait queue for pidfd notifications */ 62 wait_queue_head_t wait_pidfd; 63 struct rcu_head rcu; 64 struct upid numbers[]; 65 }; 66 67 extern struct pid init_struct_pid; 68 69 extern const struct file_operations pidfd_fops; 70 71 struct file; 72 73 extern struct pid *pidfd_pid(const struct file *file); 74 struct pid *pidfd_get_pid(unsigned int fd, unsigned int *flags); 75 struct task_struct *pidfd_get_task(int pidfd, unsigned int *flags); 76 int pidfd_create(struct pid *pid, unsigned int flags); 77 int pidfd_prepare(struct pid *pid, unsigned int flags, struct file **ret); 78 79 static inline struct pid *get_pid(struct pid *pid) 80 { 81 if (pid) 82 refcount_inc(&pid->count); 83 return pid; 84 } 85 86 extern void put_pid(struct pid *pid); 87 extern struct task_struct *pid_task(struct pid *pid, enum pid_type); 88 static inline bool pid_has_task(struct pid *pid, enum pid_type type) 89 { 90 return !hlist_empty(&pid->tasks[type]); 91 } 92 extern struct task_struct *get_pid_task(struct pid *pid, enum pid_type); 93 94 extern struct pid *get_task_pid(struct task_struct *task, enum pid_type type); 95 96 /* 97 * these helpers must be called with the tasklist_lock write-held. 98 */ 99 extern void attach_pid(struct task_struct *task, enum pid_type); 100 extern void detach_pid(struct task_struct *task, enum pid_type); 101 extern void change_pid(struct task_struct *task, enum pid_type, 102 struct pid *pid); 103 extern void exchange_tids(struct task_struct *task, struct task_struct *old); 104 extern void transfer_pid(struct task_struct *old, struct task_struct *new, 105 enum pid_type); 106 107 extern int pid_max; 108 extern int pid_max_min, pid_max_max; 109 110 /* 111 * look up a PID in the hash table. Must be called with the tasklist_lock 112 * or rcu_read_lock() held. 113 * 114 * find_pid_ns() finds the pid in the namespace specified 115 * find_vpid() finds the pid by its virtual id, i.e. in the current namespace 116 * 117 * see also find_task_by_vpid() set in include/linux/sched.h 118 */ 119 extern struct pid *find_pid_ns(int nr, struct pid_namespace *ns); 120 extern struct pid *find_vpid(int nr); 121 122 /* 123 * Lookup a PID in the hash table, and return with it's count elevated. 124 */ 125 extern struct pid *find_get_pid(int nr); 126 extern struct pid *find_ge_pid(int nr, struct pid_namespace *); 127 128 extern struct pid *alloc_pid(struct pid_namespace *ns, pid_t *set_tid, 129 size_t set_tid_size); 130 extern void free_pid(struct pid *pid); 131 extern void disable_pid_allocation(struct pid_namespace *ns); 132 133 /* 134 * ns_of_pid() returns the pid namespace in which the specified pid was 135 * allocated. 136 * 137 * NOTE: 138 * ns_of_pid() is expected to be called for a process (task) that has 139 * an attached 'struct pid' (see attach_pid(), detach_pid()) i.e @pid 140 * is expected to be non-NULL. If @pid is NULL, caller should handle 141 * the resulting NULL pid-ns. 142 */ 143 static inline struct pid_namespace *ns_of_pid(struct pid *pid) 144 { 145 struct pid_namespace *ns = NULL; 146 if (pid) 147 ns = pid->numbers[pid->level].ns; 148 return ns; 149 } 150 151 /* 152 * is_child_reaper returns true if the pid is the init process 153 * of the current namespace. As this one could be checked before 154 * pid_ns->child_reaper is assigned in copy_process, we check 155 * with the pid number. 156 */ 157 static inline bool is_child_reaper(struct pid *pid) 158 { 159 return pid->numbers[pid->level].nr == 1; 160 } 161 162 /* 163 * the helpers to get the pid's id seen from different namespaces 164 * 165 * pid_nr() : global id, i.e. the id seen from the init namespace; 166 * pid_vnr() : virtual id, i.e. the id seen from the pid namespace of 167 * current. 168 * pid_nr_ns() : id seen from the ns specified. 169 * 170 * see also task_xid_nr() etc in include/linux/sched.h 171 */ 172 173 static inline pid_t pid_nr(struct pid *pid) 174 { 175 pid_t nr = 0; 176 if (pid) 177 nr = pid->numbers[0].nr; 178 return nr; 179 } 180 181 pid_t pid_nr_ns(struct pid *pid, struct pid_namespace *ns); 182 pid_t pid_vnr(struct pid *pid); 183 184 #define do_each_pid_task(pid, type, task) \ 185 do { \ 186 if ((pid) != NULL) \ 187 hlist_for_each_entry_rcu((task), \ 188 &(pid)->tasks[type], pid_links[type]) { 189 190 /* 191 * Both old and new leaders may be attached to 192 * the same pid in the middle of de_thread(). 193 */ 194 #define while_each_pid_task(pid, type, task) \ 195 if (type == PIDTYPE_PID) \ 196 break; \ 197 } \ 198 } while (0) 199 200 #define do_each_pid_thread(pid, type, task) \ 201 do_each_pid_task(pid, type, task) { \ 202 struct task_struct *tg___ = task; \ 203 for_each_thread(tg___, task) { 204 205 #define while_each_pid_thread(pid, type, task) \ 206 } \ 207 task = tg___; \ 208 } while_each_pid_task(pid, type, task) 209 210 static inline struct pid *task_pid(struct task_struct *task) 211 { 212 return task->thread_pid; 213 } 214 215 /* 216 * the helpers to get the task's different pids as they are seen 217 * from various namespaces 218 * 219 * task_xid_nr() : global id, i.e. the id seen from the init namespace; 220 * task_xid_vnr() : virtual id, i.e. the id seen from the pid namespace of 221 * current. 222 * task_xid_nr_ns() : id seen from the ns specified; 223 * 224 * see also pid_nr() etc in include/linux/pid.h 225 */ 226 pid_t __task_pid_nr_ns(struct task_struct *task, enum pid_type type, struct pid_namespace *ns); 227 228 static inline pid_t task_pid_nr(struct task_struct *tsk) 229 { 230 return tsk->pid; 231 } 232 233 static inline pid_t task_pid_nr_ns(struct task_struct *tsk, struct pid_namespace *ns) 234 { 235 return __task_pid_nr_ns(tsk, PIDTYPE_PID, ns); 236 } 237 238 static inline pid_t task_pid_vnr(struct task_struct *tsk) 239 { 240 return __task_pid_nr_ns(tsk, PIDTYPE_PID, NULL); 241 } 242 243 244 static inline pid_t task_tgid_nr(struct task_struct *tsk) 245 { 246 return tsk->tgid; 247 } 248 249 /** 250 * pid_alive - check that a task structure is not stale 251 * @p: Task structure to be checked. 252 * 253 * Test if a process is not yet dead (at most zombie state) 254 * If pid_alive fails, then pointers within the task structure 255 * can be stale and must not be dereferenced. 256 * 257 * Return: 1 if the process is alive. 0 otherwise. 258 */ 259 static inline int pid_alive(const struct task_struct *p) 260 { 261 return p->thread_pid != NULL; 262 } 263 264 static inline pid_t task_pgrp_nr_ns(struct task_struct *tsk, struct pid_namespace *ns) 265 { 266 return __task_pid_nr_ns(tsk, PIDTYPE_PGID, ns); 267 } 268 269 static inline pid_t task_pgrp_vnr(struct task_struct *tsk) 270 { 271 return __task_pid_nr_ns(tsk, PIDTYPE_PGID, NULL); 272 } 273 274 275 static inline pid_t task_session_nr_ns(struct task_struct *tsk, struct pid_namespace *ns) 276 { 277 return __task_pid_nr_ns(tsk, PIDTYPE_SID, ns); 278 } 279 280 static inline pid_t task_session_vnr(struct task_struct *tsk) 281 { 282 return __task_pid_nr_ns(tsk, PIDTYPE_SID, NULL); 283 } 284 285 static inline pid_t task_tgid_nr_ns(struct task_struct *tsk, struct pid_namespace *ns) 286 { 287 return __task_pid_nr_ns(tsk, PIDTYPE_TGID, ns); 288 } 289 290 static inline pid_t task_tgid_vnr(struct task_struct *tsk) 291 { 292 return __task_pid_nr_ns(tsk, PIDTYPE_TGID, NULL); 293 } 294 295 static inline pid_t task_ppid_nr_ns(const struct task_struct *tsk, struct pid_namespace *ns) 296 { 297 pid_t pid = 0; 298 299 rcu_read_lock(); 300 if (pid_alive(tsk)) 301 pid = task_tgid_nr_ns(rcu_dereference(tsk->real_parent), ns); 302 rcu_read_unlock(); 303 304 return pid; 305 } 306 307 static inline pid_t task_ppid_nr(const struct task_struct *tsk) 308 { 309 return task_ppid_nr_ns(tsk, &init_pid_ns); 310 } 311 312 /* Obsolete, do not use: */ 313 static inline pid_t task_pgrp_nr(struct task_struct *tsk) 314 { 315 return task_pgrp_nr_ns(tsk, &init_pid_ns); 316 } 317 318 /** 319 * is_global_init - check if a task structure is init. Since init 320 * is free to have sub-threads we need to check tgid. 321 * @tsk: Task structure to be checked. 322 * 323 * Check if a task structure is the first user space task the kernel created. 324 * 325 * Return: 1 if the task structure is init. 0 otherwise. 326 */ 327 static inline int is_global_init(struct task_struct *tsk) 328 { 329 return task_tgid_nr(tsk) == 1; 330 } 331 332 #endif /* _LINUX_PID_H */ 333