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Linux/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/sched/rt.h>
 19 #include <linux/interrupt.h>
 20 #include <linux/mm.h>
 21 #include <linux/fs.h>
 22 #include <linux/mount.h>
 23 #include <linux/kdev_t.h>
 24 #include <linux/major.h>
 25 #include <linux/reboot.h>
 26 #include <linux/sysrq.h>
 27 #include <linux/kbd_kern.h>
 28 #include <linux/proc_fs.h>
 29 #include <linux/nmi.h>
 30 #include <linux/quotaops.h>
 31 #include <linux/perf_event.h>
 32 #include <linux/kernel.h>
 33 #include <linux/module.h>
 34 #include <linux/suspend.h>
 35 #include <linux/writeback.h>
 36 #include <linux/swap.h>
 37 #include <linux/spinlock.h>
 38 #include <linux/vt_kern.h>
 39 #include <linux/workqueue.h>
 40 #include <linux/hrtimer.h>
 41 #include <linux/oom.h>
 42 #include <linux/slab.h>
 43 #include <linux/input.h>
 44 #include <linux/uaccess.h>
 45 #include <linux/moduleparam.h>
 46 #include <linux/jiffies.h>
 47 #include <linux/syscalls.h>
 48 #include <linux/of.h>
 49 #include <linux/rcupdate.h>
 50 
 51 #include <asm/ptrace.h>
 52 #include <asm/irq_regs.h>
 53 
 54 /* Whether we react on sysrq keys or just ignore them */
 55 static int __read_mostly sysrq_enabled = CONFIG_MAGIC_SYSRQ_DEFAULT_ENABLE;
 56 static bool __read_mostly sysrq_always_enabled;
 57 
 58 static bool sysrq_on(void)
 59 {
 60         return sysrq_enabled || sysrq_always_enabled;
 61 }
 62 
 63 /*
 64  * A value of 1 means 'all', other nonzero values are an op mask:
 65  */
 66 static bool sysrq_on_mask(int mask)
 67 {
 68         return sysrq_always_enabled ||
 69                sysrq_enabled == 1 ||
 70                (sysrq_enabled & mask);
 71 }
 72 
 73 static int __init sysrq_always_enabled_setup(char *str)
 74 {
 75         sysrq_always_enabled = true;
 76         pr_info("sysrq always enabled.\n");
 77 
 78         return 1;
 79 }
 80 
 81 __setup("sysrq_always_enabled", sysrq_always_enabled_setup);
 82 
 83 
 84 static void sysrq_handle_loglevel(int key)
 85 {
 86         int i;
 87 
 88         i = key - '';
 89         console_loglevel = CONSOLE_LOGLEVEL_DEFAULT;
 90         pr_info("Loglevel set to %d\n", i);
 91         console_loglevel = i;
 92 }
 93 static struct sysrq_key_op sysrq_loglevel_op = {
 94         .handler        = sysrq_handle_loglevel,
 95         .help_msg       = "loglevel(0-9)",
 96         .action_msg     = "Changing Loglevel",
 97         .enable_mask    = SYSRQ_ENABLE_LOG,
 98 };
 99 
100 #ifdef CONFIG_VT
101 static void sysrq_handle_SAK(int key)
102 {
103         struct work_struct *SAK_work = &vc_cons[fg_console].SAK_work;
104         schedule_work(SAK_work);
105 }
106 static struct sysrq_key_op sysrq_SAK_op = {
107         .handler        = sysrq_handle_SAK,
108         .help_msg       = "sak(k)",
109         .action_msg     = "SAK",
110         .enable_mask    = SYSRQ_ENABLE_KEYBOARD,
111 };
112 #else
113 #define sysrq_SAK_op (*(struct sysrq_key_op *)NULL)
114 #endif
115 
116 #ifdef CONFIG_VT
117 static void sysrq_handle_unraw(int key)
118 {
119         vt_reset_unicode(fg_console);
120 }
121 
122 static struct sysrq_key_op sysrq_unraw_op = {
123         .handler        = sysrq_handle_unraw,
124         .help_msg       = "unraw(r)",
125         .action_msg     = "Keyboard mode set to system default",
126         .enable_mask    = SYSRQ_ENABLE_KEYBOARD,
127 };
128 #else
129 #define sysrq_unraw_op (*(struct sysrq_key_op *)NULL)
130 #endif /* CONFIG_VT */
131 
132 static void sysrq_handle_crash(int key)
133 {
134         char *killer = NULL;
135 
136         /* we need to release the RCU read lock here,
137          * otherwise we get an annoying
138          * 'BUG: sleeping function called from invalid context'
139          * complaint from the kernel before the panic.
140          */
141         rcu_read_unlock();
142         panic_on_oops = 1;      /* force panic */
143         wmb();
144         *killer = 1;
145 }
146 static struct sysrq_key_op sysrq_crash_op = {
147         .handler        = sysrq_handle_crash,
148         .help_msg       = "crash(c)",
149         .action_msg     = "Trigger a crash",
150         .enable_mask    = SYSRQ_ENABLE_DUMP,
151 };
152 
153 static void sysrq_handle_reboot(int key)
154 {
155         lockdep_off();
156         local_irq_enable();
157         emergency_restart();
158 }
159 static struct sysrq_key_op sysrq_reboot_op = {
160         .handler        = sysrq_handle_reboot,
161         .help_msg       = "reboot(b)",
162         .action_msg     = "Resetting",
163         .enable_mask    = SYSRQ_ENABLE_BOOT,
164 };
165 
166 static void sysrq_handle_sync(int key)
167 {
168         emergency_sync();
169 }
170 static struct sysrq_key_op sysrq_sync_op = {
171         .handler        = sysrq_handle_sync,
172         .help_msg       = "sync(s)",
173         .action_msg     = "Emergency Sync",
174         .enable_mask    = SYSRQ_ENABLE_SYNC,
175 };
176 
177 static void sysrq_handle_show_timers(int key)
178 {
179         sysrq_timer_list_show();
180 }
181 
182 static struct sysrq_key_op sysrq_show_timers_op = {
183         .handler        = sysrq_handle_show_timers,
184         .help_msg       = "show-all-timers(q)",
185         .action_msg     = "Show clockevent devices & pending hrtimers (no others)",
186 };
187 
188 static void sysrq_handle_mountro(int key)
189 {
190         emergency_remount();
191 }
192 static struct sysrq_key_op sysrq_mountro_op = {
193         .handler        = sysrq_handle_mountro,
194         .help_msg       = "unmount(u)",
195         .action_msg     = "Emergency Remount R/O",
196         .enable_mask    = SYSRQ_ENABLE_REMOUNT,
197 };
198 
199 #ifdef CONFIG_LOCKDEP
200 static void sysrq_handle_showlocks(int key)
201 {
202         debug_show_all_locks();
203 }
204 
205 static struct sysrq_key_op sysrq_showlocks_op = {
206         .handler        = sysrq_handle_showlocks,
207         .help_msg       = "show-all-locks(d)",
208         .action_msg     = "Show Locks Held",
209 };
210 #else
211 #define sysrq_showlocks_op (*(struct sysrq_key_op *)NULL)
212 #endif
213 
214 #ifdef CONFIG_SMP
215 static DEFINE_SPINLOCK(show_lock);
216 
217 static void showacpu(void *dummy)
218 {
219         unsigned long flags;
220 
221         /* Idle CPUs have no interesting backtrace. */
222         if (idle_cpu(smp_processor_id()))
223                 return;
224 
225         spin_lock_irqsave(&show_lock, flags);
226         pr_info("CPU%d:\n", smp_processor_id());
227         show_stack(NULL, NULL);
228         spin_unlock_irqrestore(&show_lock, flags);
229 }
230 
231 static void sysrq_showregs_othercpus(struct work_struct *dummy)
232 {
233         smp_call_function(showacpu, NULL, 0);
234 }
235 
236 static DECLARE_WORK(sysrq_showallcpus, sysrq_showregs_othercpus);
237 
238 static void sysrq_handle_showallcpus(int key)
239 {
240         /*
241          * Fall back to the workqueue based printing if the
242          * backtrace printing did not succeed or the
243          * architecture has no support for it:
244          */
245         if (!trigger_all_cpu_backtrace()) {
246                 struct pt_regs *regs = get_irq_regs();
247 
248                 if (regs) {
249                         pr_info("CPU%d:\n", smp_processor_id());
250                         show_regs(regs);
251                 }
252                 schedule_work(&sysrq_showallcpus);
253         }
254 }
255 
256 static struct sysrq_key_op sysrq_showallcpus_op = {
257         .handler        = sysrq_handle_showallcpus,
258         .help_msg       = "show-backtrace-all-active-cpus(l)",
259         .action_msg     = "Show backtrace of all active CPUs",
260         .enable_mask    = SYSRQ_ENABLE_DUMP,
261 };
262 #endif
263 
264 static void sysrq_handle_showregs(int key)
265 {
266         struct pt_regs *regs = get_irq_regs();
267         if (regs)
268                 show_regs(regs);
269         perf_event_print_debug();
270 }
271 static struct sysrq_key_op sysrq_showregs_op = {
272         .handler        = sysrq_handle_showregs,
273         .help_msg       = "show-registers(p)",
274         .action_msg     = "Show Regs",
275         .enable_mask    = SYSRQ_ENABLE_DUMP,
276 };
277 
278 static void sysrq_handle_showstate(int key)
279 {
280         show_state();
281         show_workqueue_state();
282 }
283 static struct sysrq_key_op sysrq_showstate_op = {
284         .handler        = sysrq_handle_showstate,
285         .help_msg       = "show-task-states(t)",
286         .action_msg     = "Show State",
287         .enable_mask    = SYSRQ_ENABLE_DUMP,
288 };
289 
290 static void sysrq_handle_showstate_blocked(int key)
291 {
292         show_state_filter(TASK_UNINTERRUPTIBLE);
293 }
294 static struct sysrq_key_op sysrq_showstate_blocked_op = {
295         .handler        = sysrq_handle_showstate_blocked,
296         .help_msg       = "show-blocked-tasks(w)",
297         .action_msg     = "Show Blocked State",
298         .enable_mask    = SYSRQ_ENABLE_DUMP,
299 };
300 
301 #ifdef CONFIG_TRACING
302 #include <linux/ftrace.h>
303 
304 static void sysrq_ftrace_dump(int key)
305 {
306         ftrace_dump(DUMP_ALL);
307 }
308 static struct sysrq_key_op sysrq_ftrace_dump_op = {
309         .handler        = sysrq_ftrace_dump,
310         .help_msg       = "dump-ftrace-buffer(z)",
311         .action_msg     = "Dump ftrace buffer",
312         .enable_mask    = SYSRQ_ENABLE_DUMP,
313 };
314 #else
315 #define sysrq_ftrace_dump_op (*(struct sysrq_key_op *)NULL)
316 #endif
317 
318 static void sysrq_handle_showmem(int key)
319 {
320         show_mem(0);
321 }
322 static struct sysrq_key_op sysrq_showmem_op = {
323         .handler        = sysrq_handle_showmem,
324         .help_msg       = "show-memory-usage(m)",
325         .action_msg     = "Show Memory",
326         .enable_mask    = SYSRQ_ENABLE_DUMP,
327 };
328 
329 /*
330  * Signal sysrq helper function.  Sends a signal to all user processes.
331  */
332 static void send_sig_all(int sig)
333 {
334         struct task_struct *p;
335 
336         read_lock(&tasklist_lock);
337         for_each_process(p) {
338                 if (p->flags & PF_KTHREAD)
339                         continue;
340                 if (is_global_init(p))
341                         continue;
342 
343                 do_send_sig_info(sig, SEND_SIG_FORCED, p, true);
344         }
345         read_unlock(&tasklist_lock);
346 }
347 
348 static void sysrq_handle_term(int key)
349 {
350         send_sig_all(SIGTERM);
351         console_loglevel = CONSOLE_LOGLEVEL_DEBUG;
352 }
353 static struct sysrq_key_op sysrq_term_op = {
354         .handler        = sysrq_handle_term,
355         .help_msg       = "terminate-all-tasks(e)",
356         .action_msg     = "Terminate All Tasks",
357         .enable_mask    = SYSRQ_ENABLE_SIGNAL,
358 };
359 
360 static void moom_callback(struct work_struct *ignored)
361 {
362         const gfp_t gfp_mask = GFP_KERNEL;
363         struct oom_control oc = {
364                 .zonelist = node_zonelist(first_memory_node, gfp_mask),
365                 .nodemask = NULL,
366                 .memcg = NULL,
367                 .gfp_mask = gfp_mask,
368                 .order = -1,
369         };
370 
371         mutex_lock(&oom_lock);
372         if (!out_of_memory(&oc))
373                 pr_info("OOM request ignored because killer is disabled\n");
374         mutex_unlock(&oom_lock);
375 }
376 
377 static DECLARE_WORK(moom_work, moom_callback);
378 
379 static void sysrq_handle_moom(int key)
380 {
381         schedule_work(&moom_work);
382 }
383 static struct sysrq_key_op sysrq_moom_op = {
384         .handler        = sysrq_handle_moom,
385         .help_msg       = "memory-full-oom-kill(f)",
386         .action_msg     = "Manual OOM execution",
387         .enable_mask    = SYSRQ_ENABLE_SIGNAL,
388 };
389 
390 #ifdef CONFIG_BLOCK
391 static void sysrq_handle_thaw(int key)
392 {
393         emergency_thaw_all();
394 }
395 static struct sysrq_key_op sysrq_thaw_op = {
396         .handler        = sysrq_handle_thaw,
397         .help_msg       = "thaw-filesystems(j)",
398         .action_msg     = "Emergency Thaw of all frozen filesystems",
399         .enable_mask    = SYSRQ_ENABLE_SIGNAL,
400 };
401 #endif
402 
403 static void sysrq_handle_kill(int key)
404 {
405         send_sig_all(SIGKILL);
406         console_loglevel = CONSOLE_LOGLEVEL_DEBUG;
407 }
408 static struct sysrq_key_op sysrq_kill_op = {
409         .handler        = sysrq_handle_kill,
410         .help_msg       = "kill-all-tasks(i)",
411         .action_msg     = "Kill All Tasks",
412         .enable_mask    = SYSRQ_ENABLE_SIGNAL,
413 };
414 
415 static void sysrq_handle_unrt(int key)
416 {
417         normalize_rt_tasks();
418 }
419 static struct sysrq_key_op sysrq_unrt_op = {
420         .handler        = sysrq_handle_unrt,
421         .help_msg       = "nice-all-RT-tasks(n)",
422         .action_msg     = "Nice All RT Tasks",
423         .enable_mask    = SYSRQ_ENABLE_RTNICE,
424 };
425 
426 /* Key Operations table and lock */
427 static DEFINE_SPINLOCK(sysrq_key_table_lock);
428 
429 static struct sysrq_key_op *sysrq_key_table[36] = {
430         &sysrq_loglevel_op,             /* 0 */
431         &sysrq_loglevel_op,             /* 1 */
432         &sysrq_loglevel_op,             /* 2 */
433         &sysrq_loglevel_op,             /* 3 */
434         &sysrq_loglevel_op,             /* 4 */
435         &sysrq_loglevel_op,             /* 5 */
436         &sysrq_loglevel_op,             /* 6 */
437         &sysrq_loglevel_op,             /* 7 */
438         &sysrq_loglevel_op,             /* 8 */
439         &sysrq_loglevel_op,             /* 9 */
440 
441         /*
442          * a: Don't use for system provided sysrqs, it is handled specially on
443          * sparc and will never arrive.
444          */
445         NULL,                           /* a */
446         &sysrq_reboot_op,               /* b */
447         &sysrq_crash_op,                /* c & ibm_emac driver debug */
448         &sysrq_showlocks_op,            /* d */
449         &sysrq_term_op,                 /* e */
450         &sysrq_moom_op,                 /* f */
451         /* g: May be registered for the kernel debugger */
452         NULL,                           /* g */
453         NULL,                           /* h - reserved for help */
454         &sysrq_kill_op,                 /* i */
455 #ifdef CONFIG_BLOCK
456         &sysrq_thaw_op,                 /* j */
457 #else
458         NULL,                           /* j */
459 #endif
460         &sysrq_SAK_op,                  /* k */
461 #ifdef CONFIG_SMP
462         &sysrq_showallcpus_op,          /* l */
463 #else
464         NULL,                           /* l */
465 #endif
466         &sysrq_showmem_op,              /* m */
467         &sysrq_unrt_op,                 /* n */
468         /* o: This will often be registered as 'Off' at init time */
469         NULL,                           /* o */
470         &sysrq_showregs_op,             /* p */
471         &sysrq_show_timers_op,          /* q */
472         &sysrq_unraw_op,                /* r */
473         &sysrq_sync_op,                 /* s */
474         &sysrq_showstate_op,            /* t */
475         &sysrq_mountro_op,              /* u */
476         /* v: May be registered for frame buffer console restore */
477         NULL,                           /* v */
478         &sysrq_showstate_blocked_op,    /* w */
479         /* x: May be registered on mips for TLB dump */
480         /* x: May be registered on ppc/powerpc for xmon */
481         /* x: May be registered on sparc64 for global PMU dump */
482         NULL,                           /* x */
483         /* y: May be registered on sparc64 for global register dump */
484         NULL,                           /* y */
485         &sysrq_ftrace_dump_op,          /* z */
486 };
487 
488 /* key2index calculation, -1 on invalid index */
489 static int sysrq_key_table_key2index(int key)
490 {
491         int retval;
492 
493         if ((key >= '') && (key <= '9'))
494                 retval = key - '';
495         else if ((key >= 'a') && (key <= 'z'))
496                 retval = key + 10 - 'a';
497         else
498                 retval = -1;
499         return retval;
500 }
501 
502 /*
503  * get and put functions for the table, exposed to modules.
504  */
505 struct sysrq_key_op *__sysrq_get_key_op(int key)
506 {
507         struct sysrq_key_op *op_p = NULL;
508         int i;
509 
510         i = sysrq_key_table_key2index(key);
511         if (i != -1)
512                 op_p = sysrq_key_table[i];
513 
514         return op_p;
515 }
516 
517 static void __sysrq_put_key_op(int key, struct sysrq_key_op *op_p)
518 {
519         int i = sysrq_key_table_key2index(key);
520 
521         if (i != -1)
522                 sysrq_key_table[i] = op_p;
523 }
524 
525 void __handle_sysrq(int key, bool check_mask)
526 {
527         struct sysrq_key_op *op_p;
528         int orig_log_level;
529         int i;
530 
531         rcu_sysrq_start();
532         rcu_read_lock();
533         /*
534          * Raise the apparent loglevel to maximum so that the sysrq header
535          * is shown to provide the user with positive feedback.  We do not
536          * simply emit this at KERN_EMERG as that would change message
537          * routing in the consumers of /proc/kmsg.
538          */
539         orig_log_level = console_loglevel;
540         console_loglevel = CONSOLE_LOGLEVEL_DEFAULT;
541         pr_info("SysRq : ");
542 
543         op_p = __sysrq_get_key_op(key);
544         if (op_p) {
545                 /*
546                  * Should we check for enabled operations (/proc/sysrq-trigger
547                  * should not) and is the invoked operation enabled?
548                  */
549                 if (!check_mask || sysrq_on_mask(op_p->enable_mask)) {
550                         pr_cont("%s\n", op_p->action_msg);
551                         console_loglevel = orig_log_level;
552                         op_p->handler(key);
553                 } else {
554                         pr_cont("This sysrq operation is disabled.\n");
555                 }
556         } else {
557                 pr_cont("HELP : ");
558                 /* Only print the help msg once per handler */
559                 for (i = 0; i < ARRAY_SIZE(sysrq_key_table); i++) {
560                         if (sysrq_key_table[i]) {
561                                 int j;
562 
563                                 for (j = 0; sysrq_key_table[i] !=
564                                                 sysrq_key_table[j]; j++)
565                                         ;
566                                 if (j != i)
567                                         continue;
568                                 pr_cont("%s ", sysrq_key_table[i]->help_msg);
569                         }
570                 }
571                 pr_cont("\n");
572                 console_loglevel = orig_log_level;
573         }
574         rcu_read_unlock();
575         rcu_sysrq_end();
576 }
577 
578 void handle_sysrq(int key)
579 {
580         if (sysrq_on())
581                 __handle_sysrq(key, true);
582 }
583 EXPORT_SYMBOL(handle_sysrq);
584 
585 #ifdef CONFIG_INPUT
586 static int sysrq_reset_downtime_ms;
587 
588 /* Simple translation table for the SysRq keys */
589 static const unsigned char sysrq_xlate[KEY_CNT] =
590         "\000\0331234567890-=\177\t"                    /* 0x00 - 0x0f */
591         "qwertyuiop[]\r\000as"                          /* 0x10 - 0x1f */
592         "dfghjkl;'`\000\\zxcv"                          /* 0x20 - 0x2f */
593         "bnm,./\000*\000 \000\201\202\203\204\205"      /* 0x30 - 0x3f */
594         "\206\207\210\211\212\000\000789-456+1"         /* 0x40 - 0x4f */
595         "230\177\000\000\213\214\000\000\000\000\000\000\000\000\000\000" /* 0x50 - 0x5f */
596         "\r\000/";                                      /* 0x60 - 0x6f */
597 
598 struct sysrq_state {
599         struct input_handle handle;
600         struct work_struct reinject_work;
601         unsigned long key_down[BITS_TO_LONGS(KEY_CNT)];
602         unsigned int alt;
603         unsigned int alt_use;
604         bool active;
605         bool need_reinject;
606         bool reinjecting;
607 
608         /* reset sequence handling */
609         bool reset_canceled;
610         bool reset_requested;
611         unsigned long reset_keybit[BITS_TO_LONGS(KEY_CNT)];
612         int reset_seq_len;
613         int reset_seq_cnt;
614         int reset_seq_version;
615         struct timer_list keyreset_timer;
616 };
617 
618 #define SYSRQ_KEY_RESET_MAX     20 /* Should be plenty */
619 static unsigned short sysrq_reset_seq[SYSRQ_KEY_RESET_MAX];
620 static unsigned int sysrq_reset_seq_len;
621 static unsigned int sysrq_reset_seq_version = 1;
622 
623 static void sysrq_parse_reset_sequence(struct sysrq_state *state)
624 {
625         int i;
626         unsigned short key;
627 
628         state->reset_seq_cnt = 0;
629 
630         for (i = 0; i < sysrq_reset_seq_len; i++) {
631                 key = sysrq_reset_seq[i];
632 
633                 if (key == KEY_RESERVED || key > KEY_MAX)
634                         break;
635 
636                 __set_bit(key, state->reset_keybit);
637                 state->reset_seq_len++;
638 
639                 if (test_bit(key, state->key_down))
640                         state->reset_seq_cnt++;
641         }
642 
643         /* Disable reset until old keys are not released */
644         state->reset_canceled = state->reset_seq_cnt != 0;
645 
646         state->reset_seq_version = sysrq_reset_seq_version;
647 }
648 
649 static void sysrq_do_reset(unsigned long _state)
650 {
651         struct sysrq_state *state = (struct sysrq_state *) _state;
652 
653         state->reset_requested = true;
654 
655         sys_sync();
656         kernel_restart(NULL);
657 }
658 
659 static void sysrq_handle_reset_request(struct sysrq_state *state)
660 {
661         if (state->reset_requested)
662                 __handle_sysrq(sysrq_xlate[KEY_B], false);
663 
664         if (sysrq_reset_downtime_ms)
665                 mod_timer(&state->keyreset_timer,
666                         jiffies + msecs_to_jiffies(sysrq_reset_downtime_ms));
667         else
668                 sysrq_do_reset((unsigned long)state);
669 }
670 
671 static void sysrq_detect_reset_sequence(struct sysrq_state *state,
672                                         unsigned int code, int value)
673 {
674         if (!test_bit(code, state->reset_keybit)) {
675                 /*
676                  * Pressing any key _not_ in reset sequence cancels
677                  * the reset sequence.  Also cancelling the timer in
678                  * case additional keys were pressed after a reset
679                  * has been requested.
680                  */
681                 if (value && state->reset_seq_cnt) {
682                         state->reset_canceled = true;
683                         del_timer(&state->keyreset_timer);
684                 }
685         } else if (value == 0) {
686                 /*
687                  * Key release - all keys in the reset sequence need
688                  * to be pressed and held for the reset timeout
689                  * to hold.
690                  */
691                 del_timer(&state->keyreset_timer);
692 
693                 if (--state->reset_seq_cnt == 0)
694                         state->reset_canceled = false;
695         } else if (value == 1) {
696                 /* key press, not autorepeat */
697                 if (++state->reset_seq_cnt == state->reset_seq_len &&
698                     !state->reset_canceled) {
699                         sysrq_handle_reset_request(state);
700                 }
701         }
702 }
703 
704 #ifdef CONFIG_OF
705 static void sysrq_of_get_keyreset_config(void)
706 {
707         u32 key;
708         struct device_node *np;
709         struct property *prop;
710         const __be32 *p;
711 
712         np = of_find_node_by_path("/chosen/linux,sysrq-reset-seq");
713         if (!np) {
714                 pr_debug("No sysrq node found");
715                 return;
716         }
717 
718         /* Reset in case a __weak definition was present */
719         sysrq_reset_seq_len = 0;
720 
721         of_property_for_each_u32(np, "keyset", prop, p, key) {
722                 if (key == KEY_RESERVED || key > KEY_MAX ||
723                     sysrq_reset_seq_len == SYSRQ_KEY_RESET_MAX)
724                         break;
725 
726                 sysrq_reset_seq[sysrq_reset_seq_len++] = (unsigned short)key;
727         }
728 
729         /* Get reset timeout if any. */
730         of_property_read_u32(np, "timeout-ms", &sysrq_reset_downtime_ms);
731 }
732 #else
733 static void sysrq_of_get_keyreset_config(void)
734 {
735 }
736 #endif
737 
738 static void sysrq_reinject_alt_sysrq(struct work_struct *work)
739 {
740         struct sysrq_state *sysrq =
741                         container_of(work, struct sysrq_state, reinject_work);
742         struct input_handle *handle = &sysrq->handle;
743         unsigned int alt_code = sysrq->alt_use;
744 
745         if (sysrq->need_reinject) {
746                 /* we do not want the assignment to be reordered */
747                 sysrq->reinjecting = true;
748                 mb();
749 
750                 /* Simulate press and release of Alt + SysRq */
751                 input_inject_event(handle, EV_KEY, alt_code, 1);
752                 input_inject_event(handle, EV_KEY, KEY_SYSRQ, 1);
753                 input_inject_event(handle, EV_SYN, SYN_REPORT, 1);
754 
755                 input_inject_event(handle, EV_KEY, KEY_SYSRQ, 0);
756                 input_inject_event(handle, EV_KEY, alt_code, 0);
757                 input_inject_event(handle, EV_SYN, SYN_REPORT, 1);
758 
759                 mb();
760                 sysrq->reinjecting = false;
761         }
762 }
763 
764 static bool sysrq_handle_keypress(struct sysrq_state *sysrq,
765                                   unsigned int code, int value)
766 {
767         bool was_active = sysrq->active;
768         bool suppress;
769 
770         switch (code) {
771 
772         case KEY_LEFTALT:
773         case KEY_RIGHTALT:
774                 if (!value) {
775                         /* One of ALTs is being released */
776                         if (sysrq->active && code == sysrq->alt_use)
777                                 sysrq->active = false;
778 
779                         sysrq->alt = KEY_RESERVED;
780 
781                 } else if (value != 2) {
782                         sysrq->alt = code;
783                         sysrq->need_reinject = false;
784                 }
785                 break;
786 
787         case KEY_SYSRQ:
788                 if (value == 1 && sysrq->alt != KEY_RESERVED) {
789                         sysrq->active = true;
790                         sysrq->alt_use = sysrq->alt;
791                         /*
792                          * If nothing else will be pressed we'll need
793                          * to re-inject Alt-SysRq keysroke.
794                          */
795                         sysrq->need_reinject = true;
796                 }
797 
798                 /*
799                  * Pretend that sysrq was never pressed at all. This
800                  * is needed to properly handle KGDB which will try
801                  * to release all keys after exiting debugger. If we
802                  * do not clear key bit it KGDB will end up sending
803                  * release events for Alt and SysRq, potentially
804                  * triggering print screen function.
805                  */
806                 if (sysrq->active)
807                         clear_bit(KEY_SYSRQ, sysrq->handle.dev->key);
808 
809                 break;
810 
811         default:
812                 if (sysrq->active && value && value != 2) {
813                         sysrq->need_reinject = false;
814                         __handle_sysrq(sysrq_xlate[code], true);
815                 }
816                 break;
817         }
818 
819         suppress = sysrq->active;
820 
821         if (!sysrq->active) {
822 
823                 /*
824                  * See if reset sequence has changed since the last time.
825                  */
826                 if (sysrq->reset_seq_version != sysrq_reset_seq_version)
827                         sysrq_parse_reset_sequence(sysrq);
828 
829                 /*
830                  * If we are not suppressing key presses keep track of
831                  * keyboard state so we can release keys that have been
832                  * pressed before entering SysRq mode.
833                  */
834                 if (value)
835                         set_bit(code, sysrq->key_down);
836                 else
837                         clear_bit(code, sysrq->key_down);
838 
839                 if (was_active)
840                         schedule_work(&sysrq->reinject_work);
841 
842                 /* Check for reset sequence */
843                 sysrq_detect_reset_sequence(sysrq, code, value);
844 
845         } else if (value == 0 && test_and_clear_bit(code, sysrq->key_down)) {
846                 /*
847                  * Pass on release events for keys that was pressed before
848                  * entering SysRq mode.
849                  */
850                 suppress = false;
851         }
852 
853         return suppress;
854 }
855 
856 static bool sysrq_filter(struct input_handle *handle,
857                          unsigned int type, unsigned int code, int value)
858 {
859         struct sysrq_state *sysrq = handle->private;
860         bool suppress;
861 
862         /*
863          * Do not filter anything if we are in the process of re-injecting
864          * Alt+SysRq combination.
865          */
866         if (sysrq->reinjecting)
867                 return false;
868 
869         switch (type) {
870 
871         case EV_SYN:
872                 suppress = false;
873                 break;
874 
875         case EV_KEY:
876                 suppress = sysrq_handle_keypress(sysrq, code, value);
877                 break;
878 
879         default:
880                 suppress = sysrq->active;
881                 break;
882         }
883 
884         return suppress;
885 }
886 
887 static int sysrq_connect(struct input_handler *handler,
888                          struct input_dev *dev,
889                          const struct input_device_id *id)
890 {
891         struct sysrq_state *sysrq;
892         int error;
893 
894         sysrq = kzalloc(sizeof(struct sysrq_state), GFP_KERNEL);
895         if (!sysrq)
896                 return -ENOMEM;
897 
898         INIT_WORK(&sysrq->reinject_work, sysrq_reinject_alt_sysrq);
899 
900         sysrq->handle.dev = dev;
901         sysrq->handle.handler = handler;
902         sysrq->handle.name = "sysrq";
903         sysrq->handle.private = sysrq;
904         setup_timer(&sysrq->keyreset_timer,
905                     sysrq_do_reset, (unsigned long)sysrq);
906 
907         error = input_register_handle(&sysrq->handle);
908         if (error) {
909                 pr_err("Failed to register input sysrq handler, error %d\n",
910                         error);
911                 goto err_free;
912         }
913 
914         error = input_open_device(&sysrq->handle);
915         if (error) {
916                 pr_err("Failed to open input device, error %d\n", error);
917                 goto err_unregister;
918         }
919 
920         return 0;
921 
922  err_unregister:
923         input_unregister_handle(&sysrq->handle);
924  err_free:
925         kfree(sysrq);
926         return error;
927 }
928 
929 static void sysrq_disconnect(struct input_handle *handle)
930 {
931         struct sysrq_state *sysrq = handle->private;
932 
933         input_close_device(handle);
934         cancel_work_sync(&sysrq->reinject_work);
935         del_timer_sync(&sysrq->keyreset_timer);
936         input_unregister_handle(handle);
937         kfree(sysrq);
938 }
939 
940 /*
941  * We are matching on KEY_LEFTALT instead of KEY_SYSRQ because not all
942  * keyboards have SysRq key predefined and so user may add it to keymap
943  * later, but we expect all such keyboards to have left alt.
944  */
945 static const struct input_device_id sysrq_ids[] = {
946         {
947                 .flags = INPUT_DEVICE_ID_MATCH_EVBIT |
948                                 INPUT_DEVICE_ID_MATCH_KEYBIT,
949                 .evbit = { BIT_MASK(EV_KEY) },
950                 .keybit = { BIT_MASK(KEY_LEFTALT) },
951         },
952         { },
953 };
954 
955 static struct input_handler sysrq_handler = {
956         .filter         = sysrq_filter,
957         .connect        = sysrq_connect,
958         .disconnect     = sysrq_disconnect,
959         .name           = "sysrq",
960         .id_table       = sysrq_ids,
961 };
962 
963 static bool sysrq_handler_registered;
964 
965 static inline void sysrq_register_handler(void)
966 {
967         int error;
968 
969         sysrq_of_get_keyreset_config();
970 
971         error = input_register_handler(&sysrq_handler);
972         if (error)
973                 pr_err("Failed to register input handler, error %d", error);
974         else
975                 sysrq_handler_registered = true;
976 }
977 
978 static inline void sysrq_unregister_handler(void)
979 {
980         if (sysrq_handler_registered) {
981                 input_unregister_handler(&sysrq_handler);
982                 sysrq_handler_registered = false;
983         }
984 }
985 
986 static int sysrq_reset_seq_param_set(const char *buffer,
987                                      const struct kernel_param *kp)
988 {
989         unsigned long val;
990         int error;
991 
992         error = kstrtoul(buffer, 0, &val);
993         if (error < 0)
994                 return error;
995 
996         if (val > KEY_MAX)
997                 return -EINVAL;
998 
999         *((unsigned short *)kp->arg) = val;
1000         sysrq_reset_seq_version++;
1001 
1002         return 0;
1003 }
1004 
1005 static const struct kernel_param_ops param_ops_sysrq_reset_seq = {
1006         .get    = param_get_ushort,
1007         .set    = sysrq_reset_seq_param_set,
1008 };
1009 
1010 #define param_check_sysrq_reset_seq(name, p)    \
1011         __param_check(name, p, unsigned short)
1012 
1013 /*
1014  * not really modular, but the easiest way to keep compat with existing
1015  * bootargs behaviour is to continue using module_param here.
1016  */
1017 module_param_array_named(reset_seq, sysrq_reset_seq, sysrq_reset_seq,
1018                          &sysrq_reset_seq_len, 0644);
1019 
1020 module_param_named(sysrq_downtime_ms, sysrq_reset_downtime_ms, int, 0644);
1021 
1022 #else
1023 
1024 static inline void sysrq_register_handler(void)
1025 {
1026 }
1027 
1028 static inline void sysrq_unregister_handler(void)
1029 {
1030 }
1031 
1032 #endif /* CONFIG_INPUT */
1033 
1034 int sysrq_toggle_support(int enable_mask)
1035 {
1036         bool was_enabled = sysrq_on();
1037 
1038         sysrq_enabled = enable_mask;
1039 
1040         if (was_enabled != sysrq_on()) {
1041                 if (sysrq_on())
1042                         sysrq_register_handler();
1043                 else
1044                         sysrq_unregister_handler();
1045         }
1046 
1047         return 0;
1048 }
1049 
1050 static int __sysrq_swap_key_ops(int key, struct sysrq_key_op *insert_op_p,
1051                                 struct sysrq_key_op *remove_op_p)
1052 {
1053         int retval;
1054 
1055         spin_lock(&sysrq_key_table_lock);
1056         if (__sysrq_get_key_op(key) == remove_op_p) {
1057                 __sysrq_put_key_op(key, insert_op_p);
1058                 retval = 0;
1059         } else {
1060                 retval = -1;
1061         }
1062         spin_unlock(&sysrq_key_table_lock);
1063 
1064         /*
1065          * A concurrent __handle_sysrq either got the old op or the new op.
1066          * Wait for it to go away before returning, so the code for an old
1067          * op is not freed (eg. on module unload) while it is in use.
1068          */
1069         synchronize_rcu();
1070 
1071         return retval;
1072 }
1073 
1074 int register_sysrq_key(int key, struct sysrq_key_op *op_p)
1075 {
1076         return __sysrq_swap_key_ops(key, op_p, NULL);
1077 }
1078 EXPORT_SYMBOL(register_sysrq_key);
1079 
1080 int unregister_sysrq_key(int key, struct sysrq_key_op *op_p)
1081 {
1082         return __sysrq_swap_key_ops(key, NULL, op_p);
1083 }
1084 EXPORT_SYMBOL(unregister_sysrq_key);
1085 
1086 #ifdef CONFIG_PROC_FS
1087 /*
1088  * writing 'C' to /proc/sysrq-trigger is like sysrq-C
1089  */
1090 static ssize_t write_sysrq_trigger(struct file *file, const char __user *buf,
1091                                    size_t count, loff_t *ppos)
1092 {
1093         if (count) {
1094                 char c;
1095 
1096                 if (get_user(c, buf))
1097                         return -EFAULT;
1098                 __handle_sysrq(c, false);
1099         }
1100 
1101         return count;
1102 }
1103 
1104 static const struct file_operations proc_sysrq_trigger_operations = {
1105         .write          = write_sysrq_trigger,
1106         .llseek         = noop_llseek,
1107 };
1108 
1109 static void sysrq_init_procfs(void)
1110 {
1111         if (!proc_create("sysrq-trigger", S_IWUSR, NULL,
1112                          &proc_sysrq_trigger_operations))
1113                 pr_err("Failed to register proc interface\n");
1114 }
1115 
1116 #else
1117 
1118 static inline void sysrq_init_procfs(void)
1119 {
1120 }
1121 
1122 #endif /* CONFIG_PROC_FS */
1123 
1124 static int __init sysrq_init(void)
1125 {
1126         sysrq_init_procfs();
1127 
1128         if (sysrq_on())
1129                 sysrq_register_handler();
1130 
1131         return 0;
1132 }
1133 device_initcall(sysrq_init);
1134 

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