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/buffer_head.h>          /* for fsync_bdev() */
  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
  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();
 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         for_each_process(p) {
 326                 if (p->mm && !is_global_init(p))
 327                         /* Not swapper, init nor kernel thread */
 328                         force_sig(sig, p);
 329         }
 330 }
 331
 332 static void sysrq_handle_term(int key)
 333 {
 334         send_sig_all(SIGTERM);
 335         console_loglevel = 8;
 336 }
 337 static struct sysrq_key_op sysrq_term_op = {
 338         .handler        = sysrq_handle_term,
 339         .help_msg       = "terminate-all-tasks(E)",
 340         .action_msg     = "Terminate All Tasks",
 341         .enable_mask    = SYSRQ_ENABLE_SIGNAL,
 342 };
 343
 344 static void moom_callback(struct work_struct *ignored)
 345 {
 346         out_of_memory(node_zonelist(0, GFP_KERNEL), GFP_KERNEL, 0, NULL);
 347 }
 348
 349 static DECLARE_WORK(moom_work, moom_callback);
 350
 351 static void sysrq_handle_moom(int key)
 352 {
 353         schedule_work(&moom_work);
 354 }
 355 static struct sysrq_key_op sysrq_moom_op = {
 356         .handler        = sysrq_handle_moom,
 357         .help_msg       = "memory-full-oom-kill(F)",
 358         .action_msg     = "Manual OOM execution",
 359         .enable_mask    = SYSRQ_ENABLE_SIGNAL,
 360 };
 361
 362 #ifdef CONFIG_BLOCK
 363 static void sysrq_handle_thaw(int key)
 364 {
 365         emergency_thaw_all();
 366 }
 367 static struct sysrq_key_op sysrq_thaw_op = {
 368         .handler        = sysrq_handle_thaw,
 369         .help_msg       = "thaw-filesystems(J)",
 370         .action_msg     = "Emergency Thaw of all frozen filesystems",
 371         .enable_mask    = SYSRQ_ENABLE_SIGNAL,
 372 };
 373 #endif
 374
 375 static void sysrq_handle_kill(int key)
 376 {
 377         send_sig_all(SIGKILL);
 378         console_loglevel = 8;
 379 }
 380 static struct sysrq_key_op sysrq_kill_op = {
 381         .handler        = sysrq_handle_kill,
 382         .help_msg       = "kill-all-tasks(I)",
 383         .action_msg     = "Kill All Tasks",
 384         .enable_mask    = SYSRQ_ENABLE_SIGNAL,
 385 };
 386
 387 static void sysrq_handle_unrt(int key)
 388 {
 389         normalize_rt_tasks();
 390 }
 391 static struct sysrq_key_op sysrq_unrt_op = {
 392         .handler        = sysrq_handle_unrt,
 393         .help_msg       = "nice-all-RT-tasks(N)",
 394         .action_msg     = "Nice All RT Tasks",
 395         .enable_mask    = SYSRQ_ENABLE_RTNICE,
 396 };
 397
 398 /* Key Operations table and lock */
 399 static DEFINE_SPINLOCK(sysrq_key_table_lock);
 400
 401 static struct sysrq_key_op *sysrq_key_table[36] = {
 402         &sysrq_loglevel_op,             /* 0 */
 403         &sysrq_loglevel_op,             /* 1 */
 404         &sysrq_loglevel_op,             /* 2 */
 405         &sysrq_loglevel_op,             /* 3 */
 406         &sysrq_loglevel_op,             /* 4 */
 407         &sysrq_loglevel_op,             /* 5 */
 408         &sysrq_loglevel_op,             /* 6 */
 409         &sysrq_loglevel_op,             /* 7 */
 410         &sysrq_loglevel_op,             /* 8 */
 411         &sysrq_loglevel_op,             /* 9 */
 412
 413         /*
 414          * a: Don't use for system provided sysrqs, it is handled specially on
 415          * sparc and will never arrive.
 416          */
 417         NULL,                           /* a */
 418         &sysrq_reboot_op,               /* b */
 419         &sysrq_crash_op,                /* c & ibm_emac driver debug */
 420         &sysrq_showlocks_op,            /* d */
 421         &sysrq_term_op,                 /* e */
 422         &sysrq_moom_op,                 /* f */
 423         /* g: May be registered for the kernel debugger */
 424         NULL,                           /* g */
 425         NULL,                           /* h - reserved for help */
 426         &sysrq_kill_op,                 /* i */
 427 #ifdef CONFIG_BLOCK
 428         &sysrq_thaw_op,                 /* j */
 429 #else
 430         NULL,                           /* j */
 431 #endif
 432         &sysrq_SAK_op,                  /* k */
 433 #ifdef CONFIG_SMP
 434         &sysrq_showallcpus_op,          /* l */
 435 #else
 436         NULL,                           /* l */
 437 #endif
 438         &sysrq_showmem_op,              /* m */
 439         &sysrq_unrt_op,                 /* n */
 440         /* o: This will often be registered as 'Off' at init time */
 441         NULL,                           /* o */
 442         &sysrq_showregs_op,             /* p */
 443         &sysrq_show_timers_op,          /* q */
 444         &sysrq_unraw_op,                /* r */
 445         &sysrq_sync_op,                 /* s */
 446         &sysrq_showstate_op,            /* t */
 447         &sysrq_mountro_op,              /* u */
 448         /* v: May be registered for frame buffer console restore */
 449         NULL,                           /* v */
 450         &sysrq_showstate_blocked_op,    /* w */
 451         /* x: May be registered on ppc/powerpc for xmon */
 452         NULL,                           /* x */
 453         /* y: May be registered on sparc64 for global register dump */
 454         NULL,                           /* y */
 455         &sysrq_ftrace_dump_op,          /* z */
 456 };
 457
 458 /* key2index calculation, -1 on invalid index */
 459 static int sysrq_key_table_key2index(int key)
 460 {
 461         int retval;
 462
 463         if ((key >= '0') && (key <= '9'))
 464                 retval = key - '0';
 465         else if ((key >= 'a') && (key <= 'z'))
 466                 retval = key + 10 - 'a';
 467         else
 468                 retval = -1;
 469         return retval;
 470 }
 471
 472 /*
 473  * get and put functions for the table, exposed to modules.
 474  */
 475 struct sysrq_key_op *__sysrq_get_key_op(int key)
 476 {
 477         struct sysrq_key_op *op_p = NULL;
 478         int i;
 479
 480         i = sysrq_key_table_key2index(key);
 481         if (i != -1)
 482                 op_p = sysrq_key_table[i];
 483
 484         return op_p;
 485 }
 486
 487 static void __sysrq_put_key_op(int key, struct sysrq_key_op *op_p)
 488 {
 489         int i = sysrq_key_table_key2index(key);
 490
 491         if (i != -1)
 492                 sysrq_key_table[i] = op_p;
 493 }
 494
 495 void __handle_sysrq(int key, bool check_mask)
 496 {
 497         struct sysrq_key_op *op_p;
 498         int orig_log_level;
 499         int i;
 500         unsigned long flags;
 501
 502         spin_lock_irqsave(&sysrq_key_table_lock, flags);
 503         /*
 504          * Raise the apparent loglevel to maximum so that the sysrq header
 505          * is shown to provide the user with positive feedback.  We do not
 506          * simply emit this at KERN_EMERG as that would change message
 507          * routing in the consumers of /proc/kmsg.
 508          */
 509         orig_log_level = console_loglevel;
 510         console_loglevel = 7;
 511         printk(KERN_INFO "SysRq : ");
 512
 513         op_p = __sysrq_get_key_op(key);
 514         if (op_p) {
 515                 /*
 516                  * Should we check for enabled operations (/proc/sysrq-trigger
 517                  * should not) and is the invoked operation enabled?
 518                  */
 519                 if (!check_mask || sysrq_on_mask(op_p->enable_mask)) {
 520                         printk("%s\n", op_p->action_msg);
 521                         console_loglevel = orig_log_level;
 522                         op_p->handler(key);
 523                 } else {
 524                         printk("This sysrq operation is disabled.\n");
 525                 }
 526         } else {
 527                 printk("HELP : ");
 528                 /* Only print the help msg once per handler */
 529                 for (i = 0; i < ARRAY_SIZE(sysrq_key_table); i++) {
 530                         if (sysrq_key_table[i]) {
 531                                 int j;
 532
 533                                 for (j = 0; sysrq_key_table[i] !=
 534                                                 sysrq_key_table[j]; j++)
 535                                         ;
 536                                 if (j != i)
 537                                         continue;
 538                                 printk("%s ", sysrq_key_table[i]->help_msg);
 539                         }
 540                 }
 541                 printk("\n");
 542                 console_loglevel = orig_log_level;
 543         }
 544         spin_unlock_irqrestore(&sysrq_key_table_lock, flags);
 545 }
 546
 547 void handle_sysrq(int key)
 548 {
 549         if (sysrq_on())
 550                 __handle_sysrq(key, true);
 551 }
 552 EXPORT_SYMBOL(handle_sysrq);
 553
 554 #ifdef CONFIG_INPUT
 555
 556 /* Simple translation table for the SysRq keys */
 557 static const unsigned char sysrq_xlate[KEY_CNT] =
 558         "\000\0331234567890-=\177\t"                    /* 0x00 - 0x0f */
 559         "qwertyuiop[]\r\000as"                          /* 0x10 - 0x1f */
 560         "dfghjkl;'`\000\\zxcv"                          /* 0x20 - 0x2f */
 561         "bnm,./\000*\000 \000\201\202\203\204\205"      /* 0x30 - 0x3f */
 562         "\206\207\210\211\212\000\000789-456+1"         /* 0x40 - 0x4f */
 563         "230\177\000\000\213\214\000\000\000\000\000\000\000\000\000\000" /* 0x50 - 0x5f */
 564         "\r\000/";                                      /* 0x60 - 0x6f */
 565
 566 struct sysrq_state {
 567         struct input_handle handle;
 568         struct work_struct reinject_work;
 569         unsigned long key_down[BITS_TO_LONGS(KEY_CNT)];
 570         unsigned int alt;
 571         unsigned int alt_use;
 572         bool active;
 573         bool need_reinject;
 574         bool reinjecting;
 575 };
 576
 577 static void sysrq_reinject_alt_sysrq(struct work_struct *work)
 578 {
 579         struct sysrq_state *sysrq =
 580                         container_of(work, struct sysrq_state, reinject_work);
 581         struct input_handle *handle = &sysrq->handle;
 582         unsigned int alt_code = sysrq->alt_use;
 583
 584         if (sysrq->need_reinject) {
 585                 /* we do not want the assignment to be reordered */
 586                 sysrq->reinjecting = true;
 587                 mb();
 588
 589                 /* Simulate press and release of Alt + SysRq */
 590                 input_inject_event(handle, EV_KEY, alt_code, 1);
 591                 input_inject_event(handle, EV_KEY, KEY_SYSRQ, 1);
 592                 input_inject_event(handle, EV_SYN, SYN_REPORT, 1);
 593
 594                 input_inject_event(handle, EV_KEY, KEY_SYSRQ, 0);
 595                 input_inject_event(handle, EV_KEY, alt_code, 0);
 596                 input_inject_event(handle, EV_SYN, SYN_REPORT, 1);
 597
 598                 mb();
 599                 sysrq->reinjecting = false;
 600         }
 601 }
 602
 603 static bool sysrq_filter(struct input_handle *handle,
 604                          unsigned int type, unsigned int code, int value)
 605 {
 606         struct sysrq_state *sysrq = handle->private;
 607         bool was_active = sysrq->active;
 608         bool suppress;
 609
 610         /*
 611          * Do not filter anything if we are in the process of re-injecting
 612          * Alt+SysRq combination.
 613          */
 614         if (sysrq->reinjecting)
 615                 return false;
 616
 617         switch (type) {
 618
 619         case EV_SYN:
 620                 suppress = false;
 621                 break;
 622
 623         case EV_KEY:
 624                 switch (code) {
 625
 626                 case KEY_LEFTALT:
 627                 case KEY_RIGHTALT:
 628                         if (!value) {
 629                                 /* One of ALTs is being released */
 630                                 if (sysrq->active && code == sysrq->alt_use)
 631                                         sysrq->active = false;
 632
 633                                 sysrq->alt = KEY_RESERVED;
 634
 635                         } else if (value != 2) {
 636                                 sysrq->alt = code;
 637                                 sysrq->need_reinject = false;
 638                         }
 639                         break;
 640
 641                 case KEY_SYSRQ:
 642                         if (value == 1 && sysrq->alt != KEY_RESERVED) {
 643                                 sysrq->active = true;
 644                                 sysrq->alt_use = sysrq->alt;
 645                                 /*
 646                                  * If nothing else will be pressed we'll need
 647                                  * to re-inject Alt-SysRq keysroke.
 648                                  */
 649                                 sysrq->need_reinject = true;
 650                         }
 651
 652                         /*
 653                          * Pretend that sysrq was never pressed at all. This
 654                          * is needed to properly handle KGDB which will try
 655                          * to release all keys after exiting debugger. If we
 656                          * do not clear key bit it KGDB will end up sending
 657                          * release events for Alt and SysRq, potentially
 658                          * triggering print screen function.
 659                          */
 660                         if (sysrq->active)
 661                                 clear_bit(KEY_SYSRQ, handle->dev->key);
 662
 663                         break;
 664
 665                 default:
 666                         if (sysrq->active && value && value != 2) {
 667                                 sysrq->need_reinject = false;
 668                                 __handle_sysrq(sysrq_xlate[code], true);
 669                         }
 670                         break;
 671                 }
 672
 673                 suppress = sysrq->active;
 674
 675                 if (!sysrq->active) {
 676                         /*
 677                          * If we are not suppressing key presses keep track of
 678                          * keyboard state so we can release keys that have been
 679                          * pressed before entering SysRq mode.
 680                          */
 681                         if (value)
 682                                 set_bit(code, sysrq->key_down);
 683                         else
 684                                 clear_bit(code, sysrq->key_down);
 685
 686                         if (was_active)
 687                                 schedule_work(&sysrq->reinject_work);
 688
 689                 } else if (value == 0 &&
 690                            test_and_clear_bit(code, sysrq->key_down)) {
 691                         /*
 692                          * Pass on release events for keys that was pressed before
 693                          * entering SysRq mode.
 694                          */
 695                         suppress = false;
 696                 }
 697                 break;
 698
 699         default:
 700                 suppress = sysrq->active;
 701                 break;
 702         }
 703
 704         return suppress;
 705 }
 706
 707 static int sysrq_connect(struct input_handler *handler,
 708                          struct input_dev *dev,
 709                          const struct input_device_id *id)
 710 {
 711         struct sysrq_state *sysrq;
 712         int error;
 713
 714         sysrq = kzalloc(sizeof(struct sysrq_state), GFP_KERNEL);
 715         if (!sysrq)
 716                 return -ENOMEM;
 717
 718         INIT_WORK(&sysrq->reinject_work, sysrq_reinject_alt_sysrq);
 719
 720         sysrq->handle.dev = dev;
 721         sysrq->handle.handler = handler;
 722         sysrq->handle.name = "sysrq";
 723         sysrq->handle.private = sysrq;
 724
 725         error = input_register_handle(&sysrq->handle);
 726         if (error) {
 727                 pr_err("Failed to register input sysrq handler, error %d\n",
 728                         error);
 729                 goto err_free;
 730         }
 731
 732         error = input_open_device(&sysrq->handle);
 733         if (error) {
 734                 pr_err("Failed to open input device, error %d\n", error);
 735                 goto err_unregister;
 736         }
 737
 738         return 0;
 739
 740  err_unregister:
 741         input_unregister_handle(&sysrq->handle);
 742  err_free:
 743         kfree(sysrq);
 744         return error;
 745 }
 746
 747 static void sysrq_disconnect(struct input_handle *handle)
 748 {
 749         struct sysrq_state *sysrq = handle->private;
 750
 751         input_close_device(handle);
 752         cancel_work_sync(&sysrq->reinject_work);
 753         input_unregister_handle(handle);
 754         kfree(sysrq);
 755 }
 756
 757 /*
 758  * We are matching on KEY_LEFTALT instead of KEY_SYSRQ because not all
 759  * keyboards have SysRq key predefined and so user may add it to keymap
 760  * later, but we expect all such keyboards to have left alt.
 761  */
 762 static const struct input_device_id sysrq_ids[] = {
 763         {
 764                 .flags = INPUT_DEVICE_ID_MATCH_EVBIT |
 765                                 INPUT_DEVICE_ID_MATCH_KEYBIT,
 766                 .evbit = { BIT_MASK(EV_KEY) },
 767                 .keybit = { BIT_MASK(KEY_LEFTALT) },
 768         },
 769         { },
 770 };
 771
 772 static struct input_handler sysrq_handler = {
 773         .filter         = sysrq_filter,
 774         .connect        = sysrq_connect,
 775         .disconnect     = sysrq_disconnect,
 776         .name           = "sysrq",
 777         .id_table       = sysrq_ids,
 778 };
 779
 780 static bool sysrq_handler_registered;
 781
 782 static inline void sysrq_register_handler(void)
 783 {
 784         int error;
 785
 786         error = input_register_handler(&sysrq_handler);
 787         if (error)
 788                 pr_err("Failed to register input handler, error %d", error);
 789         else
 790                 sysrq_handler_registered = true;
 791 }
 792
 793 static inline void sysrq_unregister_handler(void)
 794 {
 795         if (sysrq_handler_registered) {
 796                 input_unregister_handler(&sysrq_handler);
 797                 sysrq_handler_registered = false;
 798         }
 799 }
 800
 801 #else
 802
 803 static inline void sysrq_register_handler(void)
 804 {
 805 }
 806
 807 static inline void sysrq_unregister_handler(void)
 808 {
 809 }
 810
 811 #endif /* CONFIG_INPUT */
 812
 813 int sysrq_toggle_support(int enable_mask)
 814 {
 815         bool was_enabled = sysrq_on();
 816
 817         sysrq_enabled = enable_mask;
 818
 819         if (was_enabled != sysrq_on()) {
 820                 if (sysrq_on())
 821                         sysrq_register_handler();
 822                 else
 823                         sysrq_unregister_handler();
 824         }
 825
 826         return 0;
 827 }
 828
 829 static int __sysrq_swap_key_ops(int key, struct sysrq_key_op *insert_op_p,
 830                                 struct sysrq_key_op *remove_op_p)
 831 {
 832         int retval;
 833         unsigned long flags;
 834
 835         spin_lock_irqsave(&sysrq_key_table_lock, flags);
 836         if (__sysrq_get_key_op(key) == remove_op_p) {
 837                 __sysrq_put_key_op(key, insert_op_p);
 838                 retval = 0;
 839         } else {
 840                 retval = -1;
 841         }
 842         spin_unlock_irqrestore(&sysrq_key_table_lock, flags);
 843         return retval;
 844 }
 845
 846 int register_sysrq_key(int key, struct sysrq_key_op *op_p)
 847 {
 848         return __sysrq_swap_key_ops(key, op_p, NULL);
 849 }
 850 EXPORT_SYMBOL(register_sysrq_key);
 851
 852 int unregister_sysrq_key(int key, struct sysrq_key_op *op_p)
 853 {
 854         return __sysrq_swap_key_ops(key, NULL, op_p);
 855 }
 856 EXPORT_SYMBOL(unregister_sysrq_key);
 857
 858 #ifdef CONFIG_PROC_FS
 859 /*
 860  * writing 'C' to /proc/sysrq-trigger is like sysrq-C
 861  */
 862 static ssize_t write_sysrq_trigger(struct file *file, const char __user *buf,
 863                                    size_t count, loff_t *ppos)
 864 {
 865         if (count) {
 866                 char c;
 867
 868                 if (get_user(c, buf))
 869                         return -EFAULT;
 870                 __handle_sysrq(c, false);
 871         }
 872
 873         return count;
 874 }
 875
 876 static const struct file_operations proc_sysrq_trigger_operations = {
 877         .write          = write_sysrq_trigger,
 878         .llseek         = noop_llseek,
 879 };
 880
 881 static void sysrq_init_procfs(void)
 882 {
 883         if (!proc_create("sysrq-trigger", S_IWUSR, NULL,
 884                          &proc_sysrq_trigger_operations))
 885                 pr_err("Failed to register proc interface\n");
 886 }
 887
 888 #else
 889
 890 static inline void sysrq_init_procfs(void)
 891 {
 892 }
 893
 894 #endif /* CONFIG_PROC_FS */
 895
 896 static int __init sysrq_init(void)
 897 {
 898         sysrq_init_procfs();
 899
 900         if (sysrq_on())
 901                 sysrq_register_handler();
 902
 903         return 0;
 904 }
 905 module_init(sysrq_init);