sysrq: Fix possible race with exiting task
[linux-2.6.git] / drivers / tty / sysrq.c
1 /*
2  *      Linux Magic System Request Key Hacks
3  *
4  *      (c) 1997 Martin Mares <mj@atrey.karlin.mff.cuni.cz>
5  *      based on ideas by Pavel Machek <pavel@atrey.karlin.mff.cuni.cz>
6  *
7  *      (c) 2000 Crutcher Dunnavant <crutcher+kernel@datastacks.com>
8  *      overhauled to use key registration
9  *      based upon discusions in irc://irc.openprojects.net/#kernelnewbies
10  *
11  *      Copyright (c) 2010 Dmitry Torokhov
12  *      Input handler conversion
13  */
14
15 #define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
16
17 #include <linux/sched.h>
18 #include <linux/interrupt.h>
19 #include <linux/mm.h>
20 #include <linux/fs.h>
21 #include <linux/mount.h>
22 #include <linux/kdev_t.h>
23 #include <linux/major.h>
24 #include <linux/reboot.h>
25 #include <linux/sysrq.h>
26 #include <linux/kbd_kern.h>
27 #include <linux/proc_fs.h>
28 #include <linux/nmi.h>
29 #include <linux/quotaops.h>
30 #include <linux/perf_event.h>
31 #include <linux/kernel.h>
32 #include <linux/module.h>
33 #include <linux/suspend.h>
34 #include <linux/writeback.h>
35 #include <linux/swap.h>
36 #include <linux/spinlock.h>
37 #include <linux/vt_kern.h>
38 #include <linux/workqueue.h>
39 #include <linux/hrtimer.h>
40 #include <linux/oom.h>
41 #include <linux/slab.h>
42 #include <linux/input.h>
43 #include <linux/uaccess.h>
44
45 #include <asm/ptrace.h>
46 #include <asm/irq_regs.h>
47
48 /* Whether we react on sysrq keys or just ignore them */
49 static int __read_mostly sysrq_enabled = SYSRQ_DEFAULT_ENABLE;
50 static bool __read_mostly sysrq_always_enabled;
51
52 static bool sysrq_on(void)
53 {
54         return sysrq_enabled || sysrq_always_enabled;
55 }
56
57 /*
58  * A value of 1 means 'all', other nonzero values are an op mask:
59  */
60 static bool sysrq_on_mask(int mask)
61 {
62         return sysrq_always_enabled ||
63                sysrq_enabled == 1 ||
64                (sysrq_enabled & mask);
65 }
66
67 static int __init sysrq_always_enabled_setup(char *str)
68 {
69         sysrq_always_enabled = true;
70         pr_info("sysrq always enabled.\n");
71
72         return 1;
73 }
74
75 __setup("sysrq_always_enabled", sysrq_always_enabled_setup);
76
77
78 static void sysrq_handle_loglevel(int key)
79 {
80         int i;
81
82         i = key - '0';
83         console_loglevel = 7;
84         printk("Loglevel set to %d\n", i);
85         console_loglevel = i;
86 }
87 static struct sysrq_key_op sysrq_loglevel_op = {
88         .handler        = sysrq_handle_loglevel,
89         .help_msg       = "loglevel(0-9)",
90         .action_msg     = "Changing Loglevel",
91         .enable_mask    = SYSRQ_ENABLE_LOG,
92 };
93
94 #ifdef CONFIG_VT
95 static void sysrq_handle_SAK(int key)
96 {
97         struct work_struct *SAK_work = &vc_cons[fg_console].SAK_work;
98         schedule_work(SAK_work);
99 }
100 static struct sysrq_key_op sysrq_SAK_op = {
101         .handler        = sysrq_handle_SAK,
102         .help_msg       = "saK",
103         .action_msg     = "SAK",
104         .enable_mask    = SYSRQ_ENABLE_KEYBOARD,
105 };
106 #else
107 #define sysrq_SAK_op (*(struct sysrq_key_op *)NULL)
108 #endif
109
110 #ifdef CONFIG_VT
111 static void sysrq_handle_unraw(int key)
112 {
113         struct kbd_struct *kbd = &kbd_table[fg_console];
114
115         if (kbd)
116                 kbd->kbdmode = default_utf8 ? VC_UNICODE : VC_XLATE;
117 }
118 static struct sysrq_key_op sysrq_unraw_op = {
119         .handler        = sysrq_handle_unraw,
120         .help_msg       = "unRaw",
121         .action_msg     = "Keyboard mode set to system default",
122         .enable_mask    = SYSRQ_ENABLE_KEYBOARD,
123 };
124 #else
125 #define sysrq_unraw_op (*(struct sysrq_key_op *)NULL)
126 #endif /* CONFIG_VT */
127
128 static void sysrq_handle_crash(int key)
129 {
130         char *killer = NULL;
131
132         panic_on_oops = 1;      /* force panic */
133         wmb();
134         *killer = 1;
135 }
136 static struct sysrq_key_op sysrq_crash_op = {
137         .handler        = sysrq_handle_crash,
138         .help_msg       = "Crash",
139         .action_msg     = "Trigger a crash",
140         .enable_mask    = SYSRQ_ENABLE_DUMP,
141 };
142
143 static void sysrq_handle_reboot(int key)
144 {
145         lockdep_off();
146         local_irq_enable();
147         emergency_restart();
148 }
149 static struct sysrq_key_op sysrq_reboot_op = {
150         .handler        = sysrq_handle_reboot,
151         .help_msg       = "reBoot",
152         .action_msg     = "Resetting",
153         .enable_mask    = SYSRQ_ENABLE_BOOT,
154 };
155
156 static void sysrq_handle_sync(int key)
157 {
158         emergency_sync();
159 }
160 static struct sysrq_key_op sysrq_sync_op = {
161         .handler        = sysrq_handle_sync,
162         .help_msg       = "Sync",
163         .action_msg     = "Emergency Sync",
164         .enable_mask    = SYSRQ_ENABLE_SYNC,
165 };
166
167 static void sysrq_handle_show_timers(int key)
168 {
169         sysrq_timer_list_show();
170 }
171
172 static struct sysrq_key_op sysrq_show_timers_op = {
173         .handler        = sysrq_handle_show_timers,
174         .help_msg       = "show-all-timers(Q)",
175         .action_msg     = "Show clockevent devices & pending hrtimers (no others)",
176 };
177
178 static void sysrq_handle_mountro(int key)
179 {
180         emergency_remount();
181 }
182 static struct sysrq_key_op sysrq_mountro_op = {
183         .handler        = sysrq_handle_mountro,
184         .help_msg       = "Unmount",
185         .action_msg     = "Emergency Remount R/O",
186         .enable_mask    = SYSRQ_ENABLE_REMOUNT,
187 };
188
189 #ifdef CONFIG_LOCKDEP
190 static void sysrq_handle_showlocks(int key)
191 {
192         debug_show_all_locks();
193 }
194
195 static struct sysrq_key_op sysrq_showlocks_op = {
196         .handler        = sysrq_handle_showlocks,
197         .help_msg       = "show-all-locks(D)",
198         .action_msg     = "Show Locks Held",
199 };
200 #else
201 #define sysrq_showlocks_op (*(struct sysrq_key_op *)NULL)
202 #endif
203
204 #ifdef CONFIG_SMP
205 static DEFINE_SPINLOCK(show_lock);
206
207 static void showacpu(void *dummy)
208 {
209         unsigned long flags;
210
211         /* Idle CPUs have no interesting backtrace. */
212         if (idle_cpu(smp_processor_id()))
213                 return;
214
215         spin_lock_irqsave(&show_lock, flags);
216         printk(KERN_INFO "CPU%d:\n", smp_processor_id());
217         show_stack(NULL, NULL);
218         spin_unlock_irqrestore(&show_lock, flags);
219 }
220
221 static void sysrq_showregs_othercpus(struct work_struct *dummy)
222 {
223         smp_call_function(showacpu, NULL, 0);
224 }
225
226 static DECLARE_WORK(sysrq_showallcpus, sysrq_showregs_othercpus);
227
228 static void sysrq_handle_showallcpus(int key)
229 {
230         /*
231          * Fall back to the workqueue based printing if the
232          * backtrace printing did not succeed or the
233          * architecture has no support for it:
234          */
235         if (!trigger_all_cpu_backtrace()) {
236                 struct pt_regs *regs = get_irq_regs();
237
238                 if (regs) {
239                         printk(KERN_INFO "CPU%d:\n", smp_processor_id());
240                         show_regs(regs);
241                 }
242                 schedule_work(&sysrq_showallcpus);
243         }
244 }
245
246 static struct sysrq_key_op sysrq_showallcpus_op = {
247         .handler        = sysrq_handle_showallcpus,
248         .help_msg       = "show-backtrace-all-active-cpus(L)",
249         .action_msg     = "Show backtrace of all active CPUs",
250         .enable_mask    = SYSRQ_ENABLE_DUMP,
251 };
252 #endif
253
254 static void sysrq_handle_showregs(int key)
255 {
256         struct pt_regs *regs = get_irq_regs();
257         if (regs)
258                 show_regs(regs);
259         perf_event_print_debug();
260 }
261 static struct sysrq_key_op sysrq_showregs_op = {
262         .handler        = sysrq_handle_showregs,
263         .help_msg       = "show-registers(P)",
264         .action_msg     = "Show Regs",
265         .enable_mask    = SYSRQ_ENABLE_DUMP,
266 };
267
268 static void sysrq_handle_showstate(int key)
269 {
270         show_state();
271 }
272 static struct sysrq_key_op sysrq_showstate_op = {
273         .handler        = sysrq_handle_showstate,
274         .help_msg       = "show-task-states(T)",
275         .action_msg     = "Show State",
276         .enable_mask    = SYSRQ_ENABLE_DUMP,
277 };
278
279 static void sysrq_handle_showstate_blocked(int key)
280 {
281         show_state_filter(TASK_UNINTERRUPTIBLE);
282 }
283 static struct sysrq_key_op sysrq_showstate_blocked_op = {
284         .handler        = sysrq_handle_showstate_blocked,
285         .help_msg       = "show-blocked-tasks(W)",
286         .action_msg     = "Show Blocked State",
287         .enable_mask    = SYSRQ_ENABLE_DUMP,
288 };
289
290 #ifdef CONFIG_TRACING
291 #include <linux/ftrace.h>
292
293 static void sysrq_ftrace_dump(int key)
294 {
295         ftrace_dump(DUMP_ALL);
296 }
297 static struct sysrq_key_op sysrq_ftrace_dump_op = {
298         .handler        = sysrq_ftrace_dump,
299         .help_msg       = "dump-ftrace-buffer(Z)",
300         .action_msg     = "Dump ftrace buffer",
301         .enable_mask    = SYSRQ_ENABLE_DUMP,
302 };
303 #else
304 #define sysrq_ftrace_dump_op (*(struct sysrq_key_op *)NULL)
305 #endif
306
307 static void sysrq_handle_showmem(int key)
308 {
309         show_mem(0);
310 }
311 static struct sysrq_key_op sysrq_showmem_op = {
312         .handler        = sysrq_handle_showmem,
313         .help_msg       = "show-memory-usage(M)",
314         .action_msg     = "Show Memory",
315         .enable_mask    = SYSRQ_ENABLE_DUMP,
316 };
317
318 /*
319  * Signal sysrq helper function.  Sends a signal to all user processes.
320  */
321 static void send_sig_all(int sig)
322 {
323         struct task_struct *p;
324
325         read_lock(&tasklist_lock);
326         for_each_process(p) {
327                 if (p->mm && !is_global_init(p))
328                         /* Not swapper, init nor kernel thread */
329                         force_sig(sig, p);
330         }
331         read_unlock(&tasklist_lock);
332 }
333
334 static void sysrq_handle_term(int key)
335 {
336         send_sig_all(SIGTERM);
337         console_loglevel = 8;
338 }
339 static struct sysrq_key_op sysrq_term_op = {
340         .handler        = sysrq_handle_term,
341         .help_msg       = "terminate-all-tasks(E)",
342         .action_msg     = "Terminate All Tasks",
343         .enable_mask    = SYSRQ_ENABLE_SIGNAL,
344 };
345
346 static void moom_callback(struct work_struct *ignored)
347 {
348         out_of_memory(node_zonelist(0, GFP_KERNEL), GFP_KERNEL, 0, NULL);
349 }
350
351 static DECLARE_WORK(moom_work, moom_callback);
352
353 static void sysrq_handle_moom(int key)
354 {
355         schedule_work(&moom_work);
356 }
357 static struct sysrq_key_op sysrq_moom_op = {
358         .handler        = sysrq_handle_moom,
359         .help_msg       = "memory-full-oom-kill(F)",
360         .action_msg     = "Manual OOM execution",
361         .enable_mask    = SYSRQ_ENABLE_SIGNAL,
362 };
363
364 #ifdef CONFIG_BLOCK
365 static void sysrq_handle_thaw(int key)
366 {
367         emergency_thaw_all();
368 }
369 static struct sysrq_key_op sysrq_thaw_op = {
370         .handler        = sysrq_handle_thaw,
371         .help_msg       = "thaw-filesystems(J)",
372         .action_msg     = "Emergency Thaw of all frozen filesystems",
373         .enable_mask    = SYSRQ_ENABLE_SIGNAL,
374 };
375 #endif
376
377 static void sysrq_handle_kill(int key)
378 {
379         send_sig_all(SIGKILL);
380         console_loglevel = 8;
381 }
382 static struct sysrq_key_op sysrq_kill_op = {
383         .handler        = sysrq_handle_kill,
384         .help_msg       = "kill-all-tasks(I)",
385         .action_msg     = "Kill All Tasks",
386         .enable_mask    = SYSRQ_ENABLE_SIGNAL,
387 };
388
389 static void sysrq_handle_unrt(int key)
390 {
391         normalize_rt_tasks();
392 }
393 static struct sysrq_key_op sysrq_unrt_op = {
394         .handler        = sysrq_handle_unrt,
395         .help_msg       = "nice-all-RT-tasks(N)",
396         .action_msg     = "Nice All RT Tasks",
397         .enable_mask    = SYSRQ_ENABLE_RTNICE,
398 };
399
400 /* Key Operations table and lock */
401 static DEFINE_SPINLOCK(sysrq_key_table_lock);
402
403 static struct sysrq_key_op *sysrq_key_table[36] = {
404         &sysrq_loglevel_op,             /* 0 */
405         &sysrq_loglevel_op,             /* 1 */
406         &sysrq_loglevel_op,             /* 2 */
407         &sysrq_loglevel_op,             /* 3 */
408         &sysrq_loglevel_op,             /* 4 */
409         &sysrq_loglevel_op,             /* 5 */
410         &sysrq_loglevel_op,             /* 6 */
411         &sysrq_loglevel_op,             /* 7 */
412         &sysrq_loglevel_op,             /* 8 */
413         &sysrq_loglevel_op,             /* 9 */
414
415         /*
416          * a: Don't use for system provided sysrqs, it is handled specially on
417          * sparc and will never arrive.
418          */
419         NULL,                           /* a */
420         &sysrq_reboot_op,               /* b */
421         &sysrq_crash_op,                /* c & ibm_emac driver debug */
422         &sysrq_showlocks_op,            /* d */
423         &sysrq_term_op,                 /* e */
424         &sysrq_moom_op,                 /* f */
425         /* g: May be registered for the kernel debugger */
426         NULL,                           /* g */
427         NULL,                           /* h - reserved for help */
428         &sysrq_kill_op,                 /* i */
429 #ifdef CONFIG_BLOCK
430         &sysrq_thaw_op,                 /* j */
431 #else
432         NULL,                           /* j */
433 #endif
434         &sysrq_SAK_op,                  /* k */
435 #ifdef CONFIG_SMP
436         &sysrq_showallcpus_op,          /* l */
437 #else
438         NULL,                           /* l */
439 #endif
440         &sysrq_showmem_op,              /* m */
441         &sysrq_unrt_op,                 /* n */
442         /* o: This will often be registered as 'Off' at init time */
443         NULL,                           /* o */
444         &sysrq_showregs_op,             /* p */
445         &sysrq_show_timers_op,          /* q */
446         &sysrq_unraw_op,                /* r */
447         &sysrq_sync_op,                 /* s */
448         &sysrq_showstate_op,            /* t */
449         &sysrq_mountro_op,              /* u */
450         /* v: May be registered for frame buffer console restore */
451         NULL,                           /* v */
452         &sysrq_showstate_blocked_op,    /* w */
453         /* x: May be registered on ppc/powerpc for xmon */
454         NULL,                           /* x */
455         /* y: May be registered on sparc64 for global register dump */
456         NULL,                           /* y */
457         &sysrq_ftrace_dump_op,          /* z */
458 };
459
460 /* key2index calculation, -1 on invalid index */
461 static int sysrq_key_table_key2index(int key)
462 {
463         int retval;
464
465         if ((key >= '0') && (key <= '9'))
466                 retval = key - '0';
467         else if ((key >= 'a') && (key <= 'z'))
468                 retval = key + 10 - 'a';
469         else
470                 retval = -1;
471         return retval;
472 }
473
474 /*
475  * get and put functions for the table, exposed to modules.
476  */
477 struct sysrq_key_op *__sysrq_get_key_op(int key)
478 {
479         struct sysrq_key_op *op_p = NULL;
480         int i;
481
482         i = sysrq_key_table_key2index(key);
483         if (i != -1)
484                 op_p = sysrq_key_table[i];
485
486         return op_p;
487 }
488
489 static void __sysrq_put_key_op(int key, struct sysrq_key_op *op_p)
490 {
491         int i = sysrq_key_table_key2index(key);
492
493         if (i != -1)
494                 sysrq_key_table[i] = op_p;
495 }
496
497 void __handle_sysrq(int key, bool check_mask)
498 {
499         struct sysrq_key_op *op_p;
500         int orig_log_level;
501         int i;
502         unsigned long flags;
503
504         spin_lock_irqsave(&sysrq_key_table_lock, flags);
505         /*
506          * Raise the apparent loglevel to maximum so that the sysrq header
507          * is shown to provide the user with positive feedback.  We do not
508          * simply emit this at KERN_EMERG as that would change message
509          * routing in the consumers of /proc/kmsg.
510          */
511         orig_log_level = console_loglevel;
512         console_loglevel = 7;
513         printk(KERN_INFO "SysRq : ");
514
515         op_p = __sysrq_get_key_op(key);
516         if (op_p) {
517                 /*
518                  * Should we check for enabled operations (/proc/sysrq-trigger
519                  * should not) and is the invoked operation enabled?
520                  */
521                 if (!check_mask || sysrq_on_mask(op_p->enable_mask)) {
522                         printk("%s\n", op_p->action_msg);
523                         console_loglevel = orig_log_level;
524                         op_p->handler(key);
525                 } else {
526                         printk("This sysrq operation is disabled.\n");
527                 }
528         } else {
529                 printk("HELP : ");
530                 /* Only print the help msg once per handler */
531                 for (i = 0; i < ARRAY_SIZE(sysrq_key_table); i++) {
532                         if (sysrq_key_table[i]) {
533                                 int j;
534
535                                 for (j = 0; sysrq_key_table[i] !=
536                                                 sysrq_key_table[j]; j++)
537                                         ;
538                                 if (j != i)
539                                         continue;
540                                 printk("%s ", sysrq_key_table[i]->help_msg);
541                         }
542                 }
543                 printk("\n");
544                 console_loglevel = orig_log_level;
545         }
546         spin_unlock_irqrestore(&sysrq_key_table_lock, flags);
547 }
548
549 void handle_sysrq(int key)
550 {
551         if (sysrq_on())
552                 __handle_sysrq(key, true);
553 }
554 EXPORT_SYMBOL(handle_sysrq);
555
556 #ifdef CONFIG_INPUT
557
558 /* Simple translation table for the SysRq keys */
559 static const unsigned char sysrq_xlate[KEY_CNT] =
560         "\000\0331234567890-=\177\t"                    /* 0x00 - 0x0f */
561         "qwertyuiop[]\r\000as"                          /* 0x10 - 0x1f */
562         "dfghjkl;'`\000\\zxcv"                          /* 0x20 - 0x2f */
563         "bnm,./\000*\000 \000\201\202\203\204\205"      /* 0x30 - 0x3f */
564         "\206\207\210\211\212\000\000789-456+1"         /* 0x40 - 0x4f */
565         "230\177\000\000\213\214\000\000\000\000\000\000\000\000\000\000" /* 0x50 - 0x5f */
566         "\r\000/";                                      /* 0x60 - 0x6f */
567
568 struct sysrq_state {
569         struct input_handle handle;
570         struct work_struct reinject_work;
571         unsigned long key_down[BITS_TO_LONGS(KEY_CNT)];
572         unsigned int alt;
573         unsigned int alt_use;
574         bool active;
575         bool need_reinject;
576         bool reinjecting;
577 };
578
579 static void sysrq_reinject_alt_sysrq(struct work_struct *work)
580 {
581         struct sysrq_state *sysrq =
582                         container_of(work, struct sysrq_state, reinject_work);
583         struct input_handle *handle = &sysrq->handle;
584         unsigned int alt_code = sysrq->alt_use;
585
586         if (sysrq->need_reinject) {
587                 /* we do not want the assignment to be reordered */
588                 sysrq->reinjecting = true;
589                 mb();
590
591                 /* Simulate press and release of Alt + SysRq */
592                 input_inject_event(handle, EV_KEY, alt_code, 1);
593                 input_inject_event(handle, EV_KEY, KEY_SYSRQ, 1);
594                 input_inject_event(handle, EV_SYN, SYN_REPORT, 1);
595
596                 input_inject_event(handle, EV_KEY, KEY_SYSRQ, 0);
597                 input_inject_event(handle, EV_KEY, alt_code, 0);
598                 input_inject_event(handle, EV_SYN, SYN_REPORT, 1);
599
600                 mb();
601                 sysrq->reinjecting = false;
602         }
603 }
604
605 static bool sysrq_filter(struct input_handle *handle,
606                          unsigned int type, unsigned int code, int value)
607 {
608         struct sysrq_state *sysrq = handle->private;
609         bool was_active = sysrq->active;
610         bool suppress;
611
612         /*
613          * Do not filter anything if we are in the process of re-injecting
614          * Alt+SysRq combination.
615          */
616         if (sysrq->reinjecting)
617                 return false;
618
619         switch (type) {
620
621         case EV_SYN:
622                 suppress = false;
623                 break;
624
625         case EV_KEY:
626                 switch (code) {
627
628                 case KEY_LEFTALT:
629                 case KEY_RIGHTALT:
630                         if (!value) {
631                                 /* One of ALTs is being released */
632                                 if (sysrq->active && code == sysrq->alt_use)
633                                         sysrq->active = false;
634
635                                 sysrq->alt = KEY_RESERVED;
636
637                         } else if (value != 2) {
638                                 sysrq->alt = code;
639                                 sysrq->need_reinject = false;
640                         }
641                         break;
642
643                 case KEY_SYSRQ:
644                         if (value == 1 && sysrq->alt != KEY_RESERVED) {
645                                 sysrq->active = true;
646                                 sysrq->alt_use = sysrq->alt;
647                                 /*
648                                  * If nothing else will be pressed we'll need
649                                  * to re-inject Alt-SysRq keysroke.
650                                  */
651                                 sysrq->need_reinject = true;
652                         }
653
654                         /*
655                          * Pretend that sysrq was never pressed at all. This
656                          * is needed to properly handle KGDB which will try
657                          * to release all keys after exiting debugger. If we
658                          * do not clear key bit it KGDB will end up sending
659                          * release events for Alt and SysRq, potentially
660                          * triggering print screen function.
661                          */
662                         if (sysrq->active)
663                                 clear_bit(KEY_SYSRQ, handle->dev->key);
664
665                         break;
666
667                 default:
668                         if (sysrq->active && value && value != 2) {
669                                 sysrq->need_reinject = false;
670                                 __handle_sysrq(sysrq_xlate[code], true);
671                         }
672                         break;
673                 }
674
675                 suppress = sysrq->active;
676
677                 if (!sysrq->active) {
678                         /*
679                          * If we are not suppressing key presses keep track of
680                          * keyboard state so we can release keys that have been
681                          * pressed before entering SysRq mode.
682                          */
683                         if (value)
684                                 set_bit(code, sysrq->key_down);
685                         else
686                                 clear_bit(code, sysrq->key_down);
687
688                         if (was_active)
689                                 schedule_work(&sysrq->reinject_work);
690
691                 } else if (value == 0 &&
692                            test_and_clear_bit(code, sysrq->key_down)) {
693                         /*
694                          * Pass on release events for keys that was pressed before
695                          * entering SysRq mode.
696                          */
697                         suppress = false;
698                 }
699                 break;
700
701         default:
702                 suppress = sysrq->active;
703                 break;
704         }
705
706         return suppress;
707 }
708
709 static int sysrq_connect(struct input_handler *handler,
710                          struct input_dev *dev,
711                          const struct input_device_id *id)
712 {
713         struct sysrq_state *sysrq;
714         int error;
715
716         sysrq = kzalloc(sizeof(struct sysrq_state), GFP_KERNEL);
717         if (!sysrq)
718                 return -ENOMEM;
719
720         INIT_WORK(&sysrq->reinject_work, sysrq_reinject_alt_sysrq);
721
722         sysrq->handle.dev = dev;
723         sysrq->handle.handler = handler;
724         sysrq->handle.name = "sysrq";
725         sysrq->handle.private = sysrq;
726
727         error = input_register_handle(&sysrq->handle);
728         if (error) {
729                 pr_err("Failed to register input sysrq handler, error %d\n",
730                         error);
731                 goto err_free;
732         }
733
734         error = input_open_device(&sysrq->handle);
735         if (error) {
736                 pr_err("Failed to open input device, error %d\n", error);
737                 goto err_unregister;
738         }
739
740         return 0;
741
742  err_unregister:
743         input_unregister_handle(&sysrq->handle);
744  err_free:
745         kfree(sysrq);
746         return error;
747 }
748
749 static void sysrq_disconnect(struct input_handle *handle)
750 {
751         struct sysrq_state *sysrq = handle->private;
752
753         input_close_device(handle);
754         cancel_work_sync(&sysrq->reinject_work);
755         input_unregister_handle(handle);
756         kfree(sysrq);
757 }
758
759 /*
760  * We are matching on KEY_LEFTALT instead of KEY_SYSRQ because not all
761  * keyboards have SysRq key predefined and so user may add it to keymap
762  * later, but we expect all such keyboards to have left alt.
763  */
764 static const struct input_device_id sysrq_ids[] = {
765         {
766                 .flags = INPUT_DEVICE_ID_MATCH_EVBIT |
767                                 INPUT_DEVICE_ID_MATCH_KEYBIT,
768                 .evbit = { BIT_MASK(EV_KEY) },
769                 .keybit = { BIT_MASK(KEY_LEFTALT) },
770         },
771         { },
772 };
773
774 static struct input_handler sysrq_handler = {
775         .filter         = sysrq_filter,
776         .connect        = sysrq_connect,
777         .disconnect     = sysrq_disconnect,
778         .name           = "sysrq",
779         .id_table       = sysrq_ids,
780 };
781
782 static bool sysrq_handler_registered;
783
784 static inline void sysrq_register_handler(void)
785 {
786         int error;
787
788         error = input_register_handler(&sysrq_handler);
789         if (error)
790                 pr_err("Failed to register input handler, error %d", error);
791         else
792                 sysrq_handler_registered = true;
793 }
794
795 static inline void sysrq_unregister_handler(void)
796 {
797         if (sysrq_handler_registered) {
798                 input_unregister_handler(&sysrq_handler);
799                 sysrq_handler_registered = false;
800         }
801 }
802
803 #else
804
805 static inline void sysrq_register_handler(void)
806 {
807 }
808
809 static inline void sysrq_unregister_handler(void)
810 {
811 }
812
813 #endif /* CONFIG_INPUT */
814
815 int sysrq_toggle_support(int enable_mask)
816 {
817         bool was_enabled = sysrq_on();
818
819         sysrq_enabled = enable_mask;
820
821         if (was_enabled != sysrq_on()) {
822                 if (sysrq_on())
823                         sysrq_register_handler();
824                 else
825                         sysrq_unregister_handler();
826         }
827
828         return 0;
829 }
830
831 static int __sysrq_swap_key_ops(int key, struct sysrq_key_op *insert_op_p,
832                                 struct sysrq_key_op *remove_op_p)
833 {
834         int retval;
835         unsigned long flags;
836
837         spin_lock_irqsave(&sysrq_key_table_lock, flags);
838         if (__sysrq_get_key_op(key) == remove_op_p) {
839                 __sysrq_put_key_op(key, insert_op_p);
840                 retval = 0;
841         } else {
842                 retval = -1;
843         }
844         spin_unlock_irqrestore(&sysrq_key_table_lock, flags);
845         return retval;
846 }
847
848 int register_sysrq_key(int key, struct sysrq_key_op *op_p)
849 {
850         return __sysrq_swap_key_ops(key, op_p, NULL);
851 }
852 EXPORT_SYMBOL(register_sysrq_key);
853
854 int unregister_sysrq_key(int key, struct sysrq_key_op *op_p)
855 {
856         return __sysrq_swap_key_ops(key, NULL, op_p);
857 }
858 EXPORT_SYMBOL(unregister_sysrq_key);
859
860 #ifdef CONFIG_PROC_FS
861 /*
862  * writing 'C' to /proc/sysrq-trigger is like sysrq-C
863  */
864 static ssize_t write_sysrq_trigger(struct file *file, const char __user *buf,
865                                    size_t count, loff_t *ppos)
866 {
867         if (count) {
868                 char c;
869
870                 if (get_user(c, buf))
871                         return -EFAULT;
872                 __handle_sysrq(c, false);
873         }
874
875         return count;
876 }
877
878 static const struct file_operations proc_sysrq_trigger_operations = {
879         .write          = write_sysrq_trigger,
880         .llseek         = noop_llseek,
881 };
882
883 static void sysrq_init_procfs(void)
884 {
885         if (!proc_create("sysrq-trigger", S_IWUSR, NULL,
886                          &proc_sysrq_trigger_operations))
887                 pr_err("Failed to register proc interface\n");
888 }
889
890 #else
891
892 static inline void sysrq_init_procfs(void)
893 {
894 }
895
896 #endif /* CONFIG_PROC_FS */
897
898 static int __init sysrq_init(void)
899 {
900         sysrq_init_procfs();
901
902         if (sysrq_on())
903                 sysrq_register_handler();
904
905         return 0;
906 }
907 module_init(sysrq_init);