async, kmod: warn on synchronous request_module() from async workers
[linux-3.10.git] / kernel / kmod.c
1 /*
2         kmod, the new module loader (replaces kerneld)
3         Kirk Petersen
4
5         Reorganized not to be a daemon by Adam Richter, with guidance
6         from Greg Zornetzer.
7
8         Modified to avoid chroot and file sharing problems.
9         Mikael Pettersson
10
11         Limit the concurrent number of kmod modprobes to catch loops from
12         "modprobe needs a service that is in a module".
13         Keith Owens <kaos@ocs.com.au> December 1999
14
15         Unblock all signals when we exec a usermode process.
16         Shuu Yamaguchi <shuu@wondernetworkresources.com> December 2000
17
18         call_usermodehelper wait flag, and remove exec_usermodehelper.
19         Rusty Russell <rusty@rustcorp.com.au>  Jan 2003
20 */
21 #include <linux/module.h>
22 #include <linux/sched.h>
23 #include <linux/syscalls.h>
24 #include <linux/unistd.h>
25 #include <linux/kmod.h>
26 #include <linux/slab.h>
27 #include <linux/completion.h>
28 #include <linux/cred.h>
29 #include <linux/file.h>
30 #include <linux/fdtable.h>
31 #include <linux/workqueue.h>
32 #include <linux/security.h>
33 #include <linux/mount.h>
34 #include <linux/kernel.h>
35 #include <linux/init.h>
36 #include <linux/resource.h>
37 #include <linux/notifier.h>
38 #include <linux/suspend.h>
39 #include <linux/rwsem.h>
40 #include <linux/ptrace.h>
41 #include <linux/async.h>
42 #include <asm/uaccess.h>
43
44 #include <trace/events/module.h>
45
46 extern int max_threads;
47
48 static struct workqueue_struct *khelper_wq;
49
50 /*
51  * kmod_thread_locker is used for deadlock avoidance.  There is no explicit
52  * locking to protect this global - it is private to the singleton khelper
53  * thread and should only ever be modified by that thread.
54  */
55 static const struct task_struct *kmod_thread_locker;
56
57 #define CAP_BSET        (void *)1
58 #define CAP_PI          (void *)2
59
60 static kernel_cap_t usermodehelper_bset = CAP_FULL_SET;
61 static kernel_cap_t usermodehelper_inheritable = CAP_FULL_SET;
62 static DEFINE_SPINLOCK(umh_sysctl_lock);
63 static DECLARE_RWSEM(umhelper_sem);
64
65 #ifdef CONFIG_MODULES
66
67 /*
68         modprobe_path is set via /proc/sys.
69 */
70 char modprobe_path[KMOD_PATH_LEN] = "/sbin/modprobe";
71
72 static void free_modprobe_argv(struct subprocess_info *info)
73 {
74         kfree(info->argv[3]); /* check call_modprobe() */
75         kfree(info->argv);
76 }
77
78 static int call_modprobe(char *module_name, int wait)
79 {
80         static char *envp[] = {
81                 "HOME=/",
82                 "TERM=linux",
83                 "PATH=/sbin:/usr/sbin:/bin:/usr/bin",
84                 NULL
85         };
86
87         char **argv = kmalloc(sizeof(char *[5]), GFP_KERNEL);
88         if (!argv)
89                 goto out;
90
91         module_name = kstrdup(module_name, GFP_KERNEL);
92         if (!module_name)
93                 goto free_argv;
94
95         argv[0] = modprobe_path;
96         argv[1] = "-q";
97         argv[2] = "--";
98         argv[3] = module_name;  /* check free_modprobe_argv() */
99         argv[4] = NULL;
100
101         return call_usermodehelper_fns(modprobe_path, argv, envp,
102                 wait | UMH_KILLABLE, NULL, free_modprobe_argv, NULL);
103 free_argv:
104         kfree(argv);
105 out:
106         return -ENOMEM;
107 }
108
109 /**
110  * __request_module - try to load a kernel module
111  * @wait: wait (or not) for the operation to complete
112  * @fmt: printf style format string for the name of the module
113  * @...: arguments as specified in the format string
114  *
115  * Load a module using the user mode module loader. The function returns
116  * zero on success or a negative errno code on failure. Note that a
117  * successful module load does not mean the module did not then unload
118  * and exit on an error of its own. Callers must check that the service
119  * they requested is now available not blindly invoke it.
120  *
121  * If module auto-loading support is disabled then this function
122  * becomes a no-operation.
123  */
124 int __request_module(bool wait, const char *fmt, ...)
125 {
126         va_list args;
127         char module_name[MODULE_NAME_LEN];
128         unsigned int max_modprobes;
129         int ret;
130         static atomic_t kmod_concurrent = ATOMIC_INIT(0);
131 #define MAX_KMOD_CONCURRENT 50  /* Completely arbitrary value - KAO */
132         static int kmod_loop_msg;
133
134         /*
135          * We don't allow synchronous module loading from async.  Module
136          * init may invoke async_synchronize_full() which will end up
137          * waiting for this task which already is waiting for the module
138          * loading to complete, leading to a deadlock.
139          */
140         WARN_ON_ONCE(wait && current_is_async());
141
142         va_start(args, fmt);
143         ret = vsnprintf(module_name, MODULE_NAME_LEN, fmt, args);
144         va_end(args);
145         if (ret >= MODULE_NAME_LEN)
146                 return -ENAMETOOLONG;
147
148         ret = security_kernel_module_request(module_name);
149         if (ret)
150                 return ret;
151
152         /* If modprobe needs a service that is in a module, we get a recursive
153          * loop.  Limit the number of running kmod threads to max_threads/2 or
154          * MAX_KMOD_CONCURRENT, whichever is the smaller.  A cleaner method
155          * would be to run the parents of this process, counting how many times
156          * kmod was invoked.  That would mean accessing the internals of the
157          * process tables to get the command line, proc_pid_cmdline is static
158          * and it is not worth changing the proc code just to handle this case. 
159          * KAO.
160          *
161          * "trace the ppid" is simple, but will fail if someone's
162          * parent exits.  I think this is as good as it gets. --RR
163          */
164         max_modprobes = min(max_threads/2, MAX_KMOD_CONCURRENT);
165         atomic_inc(&kmod_concurrent);
166         if (atomic_read(&kmod_concurrent) > max_modprobes) {
167                 /* We may be blaming an innocent here, but unlikely */
168                 if (kmod_loop_msg < 5) {
169                         printk(KERN_ERR
170                                "request_module: runaway loop modprobe %s\n",
171                                module_name);
172                         kmod_loop_msg++;
173                 }
174                 atomic_dec(&kmod_concurrent);
175                 return -ENOMEM;
176         }
177
178         trace_module_request(module_name, wait, _RET_IP_);
179
180         ret = call_modprobe(module_name, wait ? UMH_WAIT_PROC : UMH_WAIT_EXEC);
181
182         atomic_dec(&kmod_concurrent);
183         return ret;
184 }
185 EXPORT_SYMBOL(__request_module);
186 #endif /* CONFIG_MODULES */
187
188 /*
189  * This is the task which runs the usermode application
190  */
191 static int ____call_usermodehelper(void *data)
192 {
193         struct subprocess_info *sub_info = data;
194         struct cred *new;
195         int retval;
196
197         spin_lock_irq(&current->sighand->siglock);
198         flush_signal_handlers(current, 1);
199         spin_unlock_irq(&current->sighand->siglock);
200
201         /* We can run anywhere, unlike our parent keventd(). */
202         set_cpus_allowed_ptr(current, cpu_all_mask);
203
204         /*
205          * Our parent is keventd, which runs with elevated scheduling priority.
206          * Avoid propagating that into the userspace child.
207          */
208         set_user_nice(current, 0);
209
210         retval = -ENOMEM;
211         new = prepare_kernel_cred(current);
212         if (!new)
213                 goto fail;
214
215         spin_lock(&umh_sysctl_lock);
216         new->cap_bset = cap_intersect(usermodehelper_bset, new->cap_bset);
217         new->cap_inheritable = cap_intersect(usermodehelper_inheritable,
218                                              new->cap_inheritable);
219         spin_unlock(&umh_sysctl_lock);
220
221         if (sub_info->init) {
222                 retval = sub_info->init(sub_info, new);
223                 if (retval) {
224                         abort_creds(new);
225                         goto fail;
226                 }
227         }
228
229         commit_creds(new);
230
231         retval = kernel_execve(sub_info->path,
232                                (const char *const *)sub_info->argv,
233                                (const char *const *)sub_info->envp);
234         if (!retval)
235                 return 0;
236
237         /* Exec failed? */
238 fail:
239         sub_info->retval = retval;
240         do_exit(0);
241 }
242
243 static int call_helper(void *data)
244 {
245         /* Worker thread started blocking khelper thread. */
246         kmod_thread_locker = current;
247         return ____call_usermodehelper(data);
248 }
249
250 static void call_usermodehelper_freeinfo(struct subprocess_info *info)
251 {
252         if (info->cleanup)
253                 (*info->cleanup)(info);
254         kfree(info);
255 }
256
257 static void umh_complete(struct subprocess_info *sub_info)
258 {
259         struct completion *comp = xchg(&sub_info->complete, NULL);
260         /*
261          * See call_usermodehelper_exec(). If xchg() returns NULL
262          * we own sub_info, the UMH_KILLABLE caller has gone away.
263          */
264         if (comp)
265                 complete(comp);
266         else
267                 call_usermodehelper_freeinfo(sub_info);
268 }
269
270 /* Keventd can't block, but this (a child) can. */
271 static int wait_for_helper(void *data)
272 {
273         struct subprocess_info *sub_info = data;
274         pid_t pid;
275
276         /* If SIGCLD is ignored sys_wait4 won't populate the status. */
277         spin_lock_irq(&current->sighand->siglock);
278         current->sighand->action[SIGCHLD-1].sa.sa_handler = SIG_DFL;
279         spin_unlock_irq(&current->sighand->siglock);
280
281         pid = kernel_thread(____call_usermodehelper, sub_info, SIGCHLD);
282         if (pid < 0) {
283                 sub_info->retval = pid;
284         } else {
285                 int ret = -ECHILD;
286                 /*
287                  * Normally it is bogus to call wait4() from in-kernel because
288                  * wait4() wants to write the exit code to a userspace address.
289                  * But wait_for_helper() always runs as keventd, and put_user()
290                  * to a kernel address works OK for kernel threads, due to their
291                  * having an mm_segment_t which spans the entire address space.
292                  *
293                  * Thus the __user pointer cast is valid here.
294                  */
295                 sys_wait4(pid, (int __user *)&ret, 0, NULL);
296
297                 /*
298                  * If ret is 0, either ____call_usermodehelper failed and the
299                  * real error code is already in sub_info->retval or
300                  * sub_info->retval is 0 anyway, so don't mess with it then.
301                  */
302                 if (ret)
303                         sub_info->retval = ret;
304         }
305
306         umh_complete(sub_info);
307         do_exit(0);
308 }
309
310 /* This is run by khelper thread  */
311 static void __call_usermodehelper(struct work_struct *work)
312 {
313         struct subprocess_info *sub_info =
314                 container_of(work, struct subprocess_info, work);
315         int wait = sub_info->wait & ~UMH_KILLABLE;
316         pid_t pid;
317
318         /* CLONE_VFORK: wait until the usermode helper has execve'd
319          * successfully We need the data structures to stay around
320          * until that is done.  */
321         if (wait == UMH_WAIT_PROC)
322                 pid = kernel_thread(wait_for_helper, sub_info,
323                                     CLONE_FS | CLONE_FILES | SIGCHLD);
324         else {
325                 pid = kernel_thread(call_helper, sub_info,
326                                     CLONE_VFORK | SIGCHLD);
327                 /* Worker thread stopped blocking khelper thread. */
328                 kmod_thread_locker = NULL;
329         }
330
331         switch (wait) {
332         case UMH_NO_WAIT:
333                 call_usermodehelper_freeinfo(sub_info);
334                 break;
335
336         case UMH_WAIT_PROC:
337                 if (pid > 0)
338                         break;
339                 /* FALLTHROUGH */
340         case UMH_WAIT_EXEC:
341                 if (pid < 0)
342                         sub_info->retval = pid;
343                 umh_complete(sub_info);
344         }
345 }
346
347 /*
348  * If set, call_usermodehelper_exec() will exit immediately returning -EBUSY
349  * (used for preventing user land processes from being created after the user
350  * land has been frozen during a system-wide hibernation or suspend operation).
351  * Should always be manipulated under umhelper_sem acquired for write.
352  */
353 static enum umh_disable_depth usermodehelper_disabled = UMH_DISABLED;
354
355 /* Number of helpers running */
356 static atomic_t running_helpers = ATOMIC_INIT(0);
357
358 /*
359  * Wait queue head used by usermodehelper_disable() to wait for all running
360  * helpers to finish.
361  */
362 static DECLARE_WAIT_QUEUE_HEAD(running_helpers_waitq);
363
364 /*
365  * Used by usermodehelper_read_lock_wait() to wait for usermodehelper_disabled
366  * to become 'false'.
367  */
368 static DECLARE_WAIT_QUEUE_HEAD(usermodehelper_disabled_waitq);
369
370 /*
371  * Time to wait for running_helpers to become zero before the setting of
372  * usermodehelper_disabled in usermodehelper_disable() fails
373  */
374 #define RUNNING_HELPERS_TIMEOUT (5 * HZ)
375
376 int usermodehelper_read_trylock(void)
377 {
378         DEFINE_WAIT(wait);
379         int ret = 0;
380
381         down_read(&umhelper_sem);
382         for (;;) {
383                 prepare_to_wait(&usermodehelper_disabled_waitq, &wait,
384                                 TASK_INTERRUPTIBLE);
385                 if (!usermodehelper_disabled)
386                         break;
387
388                 if (usermodehelper_disabled == UMH_DISABLED)
389                         ret = -EAGAIN;
390
391                 up_read(&umhelper_sem);
392
393                 if (ret)
394                         break;
395
396                 schedule();
397                 try_to_freeze();
398
399                 down_read(&umhelper_sem);
400         }
401         finish_wait(&usermodehelper_disabled_waitq, &wait);
402         return ret;
403 }
404 EXPORT_SYMBOL_GPL(usermodehelper_read_trylock);
405
406 long usermodehelper_read_lock_wait(long timeout)
407 {
408         DEFINE_WAIT(wait);
409
410         if (timeout < 0)
411                 return -EINVAL;
412
413         down_read(&umhelper_sem);
414         for (;;) {
415                 prepare_to_wait(&usermodehelper_disabled_waitq, &wait,
416                                 TASK_UNINTERRUPTIBLE);
417                 if (!usermodehelper_disabled)
418                         break;
419
420                 up_read(&umhelper_sem);
421
422                 timeout = schedule_timeout(timeout);
423                 if (!timeout)
424                         break;
425
426                 down_read(&umhelper_sem);
427         }
428         finish_wait(&usermodehelper_disabled_waitq, &wait);
429         return timeout;
430 }
431 EXPORT_SYMBOL_GPL(usermodehelper_read_lock_wait);
432
433 void usermodehelper_read_unlock(void)
434 {
435         up_read(&umhelper_sem);
436 }
437 EXPORT_SYMBOL_GPL(usermodehelper_read_unlock);
438
439 /**
440  * __usermodehelper_set_disable_depth - Modify usermodehelper_disabled.
441  * @depth: New value to assign to usermodehelper_disabled.
442  *
443  * Change the value of usermodehelper_disabled (under umhelper_sem locked for
444  * writing) and wakeup tasks waiting for it to change.
445  */
446 void __usermodehelper_set_disable_depth(enum umh_disable_depth depth)
447 {
448         down_write(&umhelper_sem);
449         usermodehelper_disabled = depth;
450         wake_up(&usermodehelper_disabled_waitq);
451         up_write(&umhelper_sem);
452 }
453
454 /**
455  * __usermodehelper_disable - Prevent new helpers from being started.
456  * @depth: New value to assign to usermodehelper_disabled.
457  *
458  * Set usermodehelper_disabled to @depth and wait for running helpers to exit.
459  */
460 int __usermodehelper_disable(enum umh_disable_depth depth)
461 {
462         long retval;
463
464         if (!depth)
465                 return -EINVAL;
466
467         down_write(&umhelper_sem);
468         usermodehelper_disabled = depth;
469         up_write(&umhelper_sem);
470
471         /*
472          * From now on call_usermodehelper_exec() won't start any new
473          * helpers, so it is sufficient if running_helpers turns out to
474          * be zero at one point (it may be increased later, but that
475          * doesn't matter).
476          */
477         retval = wait_event_timeout(running_helpers_waitq,
478                                         atomic_read(&running_helpers) == 0,
479                                         RUNNING_HELPERS_TIMEOUT);
480         if (retval)
481                 return 0;
482
483         __usermodehelper_set_disable_depth(UMH_ENABLED);
484         return -EAGAIN;
485 }
486
487 static void helper_lock(void)
488 {
489         atomic_inc(&running_helpers);
490         smp_mb__after_atomic_inc();
491 }
492
493 static void helper_unlock(void)
494 {
495         if (atomic_dec_and_test(&running_helpers))
496                 wake_up(&running_helpers_waitq);
497 }
498
499 /**
500  * call_usermodehelper_setup - prepare to call a usermode helper
501  * @path: path to usermode executable
502  * @argv: arg vector for process
503  * @envp: environment for process
504  * @gfp_mask: gfp mask for memory allocation
505  *
506  * Returns either %NULL on allocation failure, or a subprocess_info
507  * structure.  This should be passed to call_usermodehelper_exec to
508  * exec the process and free the structure.
509  */
510 static
511 struct subprocess_info *call_usermodehelper_setup(char *path, char **argv,
512                                                   char **envp, gfp_t gfp_mask)
513 {
514         struct subprocess_info *sub_info;
515         sub_info = kzalloc(sizeof(struct subprocess_info), gfp_mask);
516         if (!sub_info)
517                 goto out;
518
519         INIT_WORK(&sub_info->work, __call_usermodehelper);
520         sub_info->path = path;
521         sub_info->argv = argv;
522         sub_info->envp = envp;
523   out:
524         return sub_info;
525 }
526
527 /**
528  * call_usermodehelper_setfns - set a cleanup/init function
529  * @info: a subprocess_info returned by call_usermodehelper_setup
530  * @cleanup: a cleanup function
531  * @init: an init function
532  * @data: arbitrary context sensitive data
533  *
534  * The init function is used to customize the helper process prior to
535  * exec.  A non-zero return code causes the process to error out, exit,
536  * and return the failure to the calling process
537  *
538  * The cleanup function is just before ethe subprocess_info is about to
539  * be freed.  This can be used for freeing the argv and envp.  The
540  * Function must be runnable in either a process context or the
541  * context in which call_usermodehelper_exec is called.
542  */
543 static
544 void call_usermodehelper_setfns(struct subprocess_info *info,
545                     int (*init)(struct subprocess_info *info, struct cred *new),
546                     void (*cleanup)(struct subprocess_info *info),
547                     void *data)
548 {
549         info->cleanup = cleanup;
550         info->init = init;
551         info->data = data;
552 }
553
554 /**
555  * call_usermodehelper_exec - start a usermode application
556  * @sub_info: information about the subprocessa
557  * @wait: wait for the application to finish and return status.
558  *        when -1 don't wait at all, but you get no useful error back when
559  *        the program couldn't be exec'ed. This makes it safe to call
560  *        from interrupt context.
561  *
562  * Runs a user-space application.  The application is started
563  * asynchronously if wait is not set, and runs as a child of keventd.
564  * (ie. it runs with full root capabilities).
565  */
566 static
567 int call_usermodehelper_exec(struct subprocess_info *sub_info, int wait)
568 {
569         DECLARE_COMPLETION_ONSTACK(done);
570         int retval = 0;
571
572         helper_lock();
573         if (sub_info->path[0] == '\0')
574                 goto out;
575
576         if (!khelper_wq || usermodehelper_disabled) {
577                 retval = -EBUSY;
578                 goto out;
579         }
580         /*
581          * Worker thread must not wait for khelper thread at below
582          * wait_for_completion() if the thread was created with CLONE_VFORK
583          * flag, for khelper thread is already waiting for the thread at
584          * wait_for_completion() in do_fork().
585          */
586         if (wait != UMH_NO_WAIT && current == kmod_thread_locker) {
587                 retval = -EBUSY;
588                 goto out;
589         }
590
591         sub_info->complete = &done;
592         sub_info->wait = wait;
593
594         queue_work(khelper_wq, &sub_info->work);
595         if (wait == UMH_NO_WAIT)        /* task has freed sub_info */
596                 goto unlock;
597
598         if (wait & UMH_KILLABLE) {
599                 retval = wait_for_completion_killable(&done);
600                 if (!retval)
601                         goto wait_done;
602
603                 /* umh_complete() will see NULL and free sub_info */
604                 if (xchg(&sub_info->complete, NULL))
605                         goto unlock;
606                 /* fallthrough, umh_complete() was already called */
607         }
608
609         wait_for_completion(&done);
610 wait_done:
611         retval = sub_info->retval;
612 out:
613         call_usermodehelper_freeinfo(sub_info);
614 unlock:
615         helper_unlock();
616         return retval;
617 }
618
619 /*
620  * call_usermodehelper_fns() will not run the caller-provided cleanup function
621  * if a memory allocation failure is experienced.  So the caller might need to
622  * check the call_usermodehelper_fns() return value: if it is -ENOMEM, perform
623  * the necessaary cleanup within the caller.
624  */
625 int call_usermodehelper_fns(
626         char *path, char **argv, char **envp, int wait,
627         int (*init)(struct subprocess_info *info, struct cred *new),
628         void (*cleanup)(struct subprocess_info *), void *data)
629 {
630         struct subprocess_info *info;
631         gfp_t gfp_mask = (wait == UMH_NO_WAIT) ? GFP_ATOMIC : GFP_KERNEL;
632
633         info = call_usermodehelper_setup(path, argv, envp, gfp_mask);
634
635         if (info == NULL)
636                 return -ENOMEM;
637
638         call_usermodehelper_setfns(info, init, cleanup, data);
639
640         return call_usermodehelper_exec(info, wait);
641 }
642 EXPORT_SYMBOL(call_usermodehelper_fns);
643
644 static int proc_cap_handler(struct ctl_table *table, int write,
645                          void __user *buffer, size_t *lenp, loff_t *ppos)
646 {
647         struct ctl_table t;
648         unsigned long cap_array[_KERNEL_CAPABILITY_U32S];
649         kernel_cap_t new_cap;
650         int err, i;
651
652         if (write && (!capable(CAP_SETPCAP) ||
653                       !capable(CAP_SYS_MODULE)))
654                 return -EPERM;
655
656         /*
657          * convert from the global kernel_cap_t to the ulong array to print to
658          * userspace if this is a read.
659          */
660         spin_lock(&umh_sysctl_lock);
661         for (i = 0; i < _KERNEL_CAPABILITY_U32S; i++)  {
662                 if (table->data == CAP_BSET)
663                         cap_array[i] = usermodehelper_bset.cap[i];
664                 else if (table->data == CAP_PI)
665                         cap_array[i] = usermodehelper_inheritable.cap[i];
666                 else
667                         BUG();
668         }
669         spin_unlock(&umh_sysctl_lock);
670
671         t = *table;
672         t.data = &cap_array;
673
674         /*
675          * actually read or write and array of ulongs from userspace.  Remember
676          * these are least significant 32 bits first
677          */
678         err = proc_doulongvec_minmax(&t, write, buffer, lenp, ppos);
679         if (err < 0)
680                 return err;
681
682         /*
683          * convert from the sysctl array of ulongs to the kernel_cap_t
684          * internal representation
685          */
686         for (i = 0; i < _KERNEL_CAPABILITY_U32S; i++)
687                 new_cap.cap[i] = cap_array[i];
688
689         /*
690          * Drop everything not in the new_cap (but don't add things)
691          */
692         spin_lock(&umh_sysctl_lock);
693         if (write) {
694                 if (table->data == CAP_BSET)
695                         usermodehelper_bset = cap_intersect(usermodehelper_bset, new_cap);
696                 if (table->data == CAP_PI)
697                         usermodehelper_inheritable = cap_intersect(usermodehelper_inheritable, new_cap);
698         }
699         spin_unlock(&umh_sysctl_lock);
700
701         return 0;
702 }
703
704 struct ctl_table usermodehelper_table[] = {
705         {
706                 .procname       = "bset",
707                 .data           = CAP_BSET,
708                 .maxlen         = _KERNEL_CAPABILITY_U32S * sizeof(unsigned long),
709                 .mode           = 0600,
710                 .proc_handler   = proc_cap_handler,
711         },
712         {
713                 .procname       = "inheritable",
714                 .data           = CAP_PI,
715                 .maxlen         = _KERNEL_CAPABILITY_U32S * sizeof(unsigned long),
716                 .mode           = 0600,
717                 .proc_handler   = proc_cap_handler,
718         },
719         { }
720 };
721
722 void __init usermodehelper_init(void)
723 {
724         khelper_wq = create_singlethread_workqueue("khelper");
725         BUG_ON(!khelper_wq);
726 }