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