1 /* Kernel thread helper functions. 2 * Copyright (C) 2004 IBM Corporation, Rusty Russell. 3 * 4 * Creation is done via keventd, so that we get a clean environment 5 * even if we're invoked from userspace (think modprobe, hotplug cpu, 6 * etc.). 7 */ 8 #include <linux/sched.h> 9 #include <linux/kthread.h> 10 #include <linux/completion.h> 11 #include <linux/err.h> 12 #include <linux/unistd.h> 13 #include <linux/file.h> 14 #include <linux/module.h> 15 #include <linux/mutex.h> 16 #include <asm/semaphore.h> 17 18 /* 19 * We dont want to execute off keventd since it might 20 * hold a semaphore our callers hold too: 21 */ 22 static struct workqueue_struct *helper_wq; 23 24 struct kthread_create_info 25 { 26 /* Information passed to kthread() from keventd. */ 27 int (*threadfn)(void *data); 28 void *data; 29 struct completion started; 30 31 /* Result passed back to kthread_create() from keventd. */ 32 struct task_struct *result; 33 struct completion done; 34 }; 35 36 struct kthread_stop_info 37 { 38 struct task_struct *k; 39 int err; 40 struct completion done; 41 }; 42 43 /* Thread stopping is done by setthing this var: lock serializes 44 * multiple kthread_stop calls. */ 45 static DEFINE_MUTEX(kthread_stop_lock); 46 static struct kthread_stop_info kthread_stop_info; 47 48 /** 49 * kthread_should_stop - should this kthread return now? 50 * 51 * When someone calls kthread_stop on your kthread, it will be woken 52 * and this will return true. You should then return, and your return 53 * value will be passed through to kthread_stop(). 54 */ 55 int kthread_should_stop(void) 56 { 57 return (kthread_stop_info.k == current); 58 } 59 EXPORT_SYMBOL(kthread_should_stop); 60 61 static void kthread_exit_files(void) 62 { 63 struct fs_struct *fs; 64 struct task_struct *tsk = current; 65 66 exit_fs(tsk); /* current->fs->count--; */ 67 fs = init_task.fs; 68 tsk->fs = fs; 69 atomic_inc(&fs->count); 70 exit_files(tsk); 71 current->files = init_task.files; 72 atomic_inc(&tsk->files->count); 73 } 74 75 static int kthread(void *_create) 76 { 77 struct kthread_create_info *create = _create; 78 int (*threadfn)(void *data); 79 void *data; 80 sigset_t blocked; 81 int ret = -EINTR; 82 83 kthread_exit_files(); 84 85 /* Copy data: it's on keventd's stack */ 86 threadfn = create->threadfn; 87 data = create->data; 88 89 /* Block and flush all signals (in case we're not from keventd). */ 90 sigfillset(&blocked); 91 sigprocmask(SIG_BLOCK, &blocked, NULL); 92 flush_signals(current); 93 94 /* By default we can run anywhere, unlike keventd. */ 95 set_cpus_allowed(current, CPU_MASK_ALL); 96 97 /* OK, tell user we're spawned, wait for stop or wakeup */ 98 __set_current_state(TASK_INTERRUPTIBLE); 99 complete(&create->started); 100 schedule(); 101 102 if (!kthread_should_stop()) 103 ret = threadfn(data); 104 105 /* It might have exited on its own, w/o kthread_stop. Check. */ 106 if (kthread_should_stop()) { 107 kthread_stop_info.err = ret; 108 complete(&kthread_stop_info.done); 109 } 110 return 0; 111 } 112 113 /* We are keventd: create a thread. */ 114 static void keventd_create_kthread(void *_create) 115 { 116 struct kthread_create_info *create = _create; 117 int pid; 118 119 /* We want our own signal handler (we take no signals by default). */ 120 pid = kernel_thread(kthread, create, CLONE_FS | CLONE_FILES | SIGCHLD); 121 if (pid < 0) { 122 create->result = ERR_PTR(pid); 123 } else { 124 wait_for_completion(&create->started); 125 read_lock(&tasklist_lock); 126 create->result = find_task_by_pid(pid); 127 read_unlock(&tasklist_lock); 128 } 129 complete(&create->done); 130 } 131 132 /** 133 * kthread_create - create a kthread. 134 * @threadfn: the function to run until signal_pending(current). 135 * @data: data ptr for @threadfn. 136 * @namefmt: printf-style name for the thread. 137 * 138 * Description: This helper function creates and names a kernel 139 * thread. The thread will be stopped: use wake_up_process() to start 140 * it. See also kthread_run(), kthread_create_on_cpu(). 141 * 142 * When woken, the thread will run @threadfn() with @data as its 143 * argument. @threadfn can either call do_exit() directly if it is a 144 * standalone thread for which noone will call kthread_stop(), or 145 * return when 'kthread_should_stop()' is true (which means 146 * kthread_stop() has been called). The return value should be zero 147 * or a negative error number; it will be passed to kthread_stop(). 148 * 149 * Returns a task_struct or ERR_PTR(-ENOMEM). 150 */ 151 struct task_struct *kthread_create(int (*threadfn)(void *data), 152 void *data, 153 const char namefmt[], 154 ...) 155 { 156 struct kthread_create_info create; 157 DECLARE_WORK(work, keventd_create_kthread, &create); 158 159 create.threadfn = threadfn; 160 create.data = data; 161 init_completion(&create.started); 162 init_completion(&create.done); 163 164 /* 165 * The workqueue needs to start up first: 166 */ 167 if (!helper_wq) 168 work.func(work.data); 169 else { 170 queue_work(helper_wq, &work); 171 wait_for_completion(&create.done); 172 } 173 if (!IS_ERR(create.result)) { 174 va_list args; 175 va_start(args, namefmt); 176 vsnprintf(create.result->comm, sizeof(create.result->comm), 177 namefmt, args); 178 va_end(args); 179 } 180 181 return create.result; 182 } 183 EXPORT_SYMBOL(kthread_create); 184 185 /** 186 * kthread_bind - bind a just-created kthread to a cpu. 187 * @k: thread created by kthread_create(). 188 * @cpu: cpu (might not be online, must be possible) for @k to run on. 189 * 190 * Description: This function is equivalent to set_cpus_allowed(), 191 * except that @cpu doesn't need to be online, and the thread must be 192 * stopped (i.e., just returned from kthread_create(). 193 */ 194 void kthread_bind(struct task_struct *k, unsigned int cpu) 195 { 196 BUG_ON(k->state != TASK_INTERRUPTIBLE); 197 /* Must have done schedule() in kthread() before we set_task_cpu */ 198 wait_task_inactive(k); 199 set_task_cpu(k, cpu); 200 k->cpus_allowed = cpumask_of_cpu(cpu); 201 } 202 EXPORT_SYMBOL(kthread_bind); 203 204 /** 205 * kthread_stop - stop a thread created by kthread_create(). 206 * @k: thread created by kthread_create(). 207 * 208 * Sets kthread_should_stop() for @k to return true, wakes it, and 209 * waits for it to exit. Your threadfn() must not call do_exit() 210 * itself if you use this function! This can also be called after 211 * kthread_create() instead of calling wake_up_process(): the thread 212 * will exit without calling threadfn(). 213 * 214 * Returns the result of threadfn(), or %-EINTR if wake_up_process() 215 * was never called. 216 */ 217 int kthread_stop(struct task_struct *k) 218 { 219 return kthread_stop_sem(k, NULL); 220 } 221 EXPORT_SYMBOL(kthread_stop); 222 223 /** 224 * kthread_stop_sem - stop a thread created by kthread_create(). 225 * @k: thread created by kthread_create(). 226 * @s: semaphore that @k waits on while idle. 227 * 228 * Does essentially the same thing as kthread_stop() above, but wakes 229 * @k by calling up(@s). 230 * 231 * Returns the result of threadfn(), or %-EINTR if wake_up_process() 232 * was never called. 233 */ 234 int kthread_stop_sem(struct task_struct *k, struct semaphore *s) 235 { 236 int ret; 237 238 mutex_lock(&kthread_stop_lock); 239 240 /* It could exit after stop_info.k set, but before wake_up_process. */ 241 get_task_struct(k); 242 243 /* Must init completion *before* thread sees kthread_stop_info.k */ 244 init_completion(&kthread_stop_info.done); 245 smp_wmb(); 246 247 /* Now set kthread_should_stop() to true, and wake it up. */ 248 kthread_stop_info.k = k; 249 if (s) 250 up(s); 251 else 252 wake_up_process(k); 253 put_task_struct(k); 254 255 /* Once it dies, reset stop ptr, gather result and we're done. */ 256 wait_for_completion(&kthread_stop_info.done); 257 kthread_stop_info.k = NULL; 258 ret = kthread_stop_info.err; 259 mutex_unlock(&kthread_stop_lock); 260 261 return ret; 262 } 263 EXPORT_SYMBOL(kthread_stop_sem); 264 265 static __init int helper_init(void) 266 { 267 helper_wq = create_singlethread_workqueue("kthread"); 268 BUG_ON(!helper_wq); 269 270 return 0; 271 } 272 273 core_initcall(helper_init); 274