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