kernel/debug/debug_core.c

   1 /*
   2  * Kernel Debug Core
   3  *
   4  * Maintainer: Jason Wessel <jason.wessel@windriver.com>
   5  *
   6  * Copyright (C) 2000-2001 VERITAS Software Corporation.
   7  * Copyright (C) 2002-2004 Timesys Corporation
   8  * Copyright (C) 2003-2004 Amit S. Kale <amitkale@linsyssoft.com>
   9  * Copyright (C) 2004 Pavel Machek <pavel@ucw.cz>
  10  * Copyright (C) 2004-2006 Tom Rini <trini@kernel.crashing.org>
  11  * Copyright (C) 2004-2006 LinSysSoft Technologies Pvt. Ltd.
  12  * Copyright (C) 2005-2009 Wind River Systems, Inc.
  13  * Copyright (C) 2007 MontaVista Software, Inc.
  14  * Copyright (C) 2008 Red Hat, Inc., Ingo Molnar <mingo@redhat.com>
  15  *
  16  * Contributors at various stages not listed above:
  17  *  Jason Wessel ( jason.wessel@windriver.com )
  18  *  George Anzinger <george@mvista.com>
  19  *  Anurekh Saxena (anurekh.saxena@timesys.com)
  20  *  Lake Stevens Instrument Division (Glenn Engel)
  21  *  Jim Kingdon, Cygnus Support.
  22  *
  23  * Original KGDB stub: David Grothe <dave@gcom.com>,
  24  * Tigran Aivazian <tigran@sco.com>
  25  *
  26  * This file is licensed under the terms of the GNU General Public License
  27  * version 2. This program is licensed "as is" without any warranty of any
  28  * kind, whether express or implied.
  29  */
  30
  31 #define pr_fmt(fmt) "KGDB: " fmt
  32
  33 #include <linux/pid_namespace.h>
  34 #include <linux/clocksource.h>
  35 #include <linux/serial_core.h>
  36 #include <linux/interrupt.h>
  37 #include <linux/spinlock.h>
  38 #include <linux/console.h>
  39 #include <linux/threads.h>
  40 #include <linux/uaccess.h>
  41 #include <linux/kernel.h>
  42 #include <linux/module.h>
  43 #include <linux/ptrace.h>
  44 #include <linux/string.h>
  45 #include <linux/delay.h>
  46 #include <linux/sched.h>
  47 #include <linux/sysrq.h>
  48 #include <linux/reboot.h>
  49 #include <linux/init.h>
  50 #include <linux/kgdb.h>
  51 #include <linux/kdb.h>
  52 #include <linux/nmi.h>
  53 #include <linux/pid.h>
  54 #include <linux/smp.h>
  55 #include <linux/mm.h>
  56 #include <linux/vmacache.h>
  57 #include <linux/rcupdate.h>
  58
  59 #include <asm/cacheflush.h>
  60 #include <asm/byteorder.h>
  61 #include <linux/atomic.h>
  62
  63 #include "debug_core.h"
  64
  65 static int kgdb_break_asap;
  66
  67 struct debuggerinfo_struct kgdb_info[NR_CPUS];
  68
  69 /**
  70  * kgdb_connected - Is a host GDB connected to us?
  71  */
  72 int                             kgdb_connected;
  73 EXPORT_SYMBOL_GPL(kgdb_connected);
  74
  75 /* All the KGDB handlers are installed */
  76 int                     kgdb_io_module_registered;
  77
  78 /* Guard for recursive entry */
  79 static int                      exception_level;
  80
  81 struct kgdb_io          *dbg_io_ops;
  82 static DEFINE_SPINLOCK(kgdb_registration_lock);
  83
  84 /* Action for the reboot notifiter, a global allow kdb to change it */
  85 static int kgdbreboot;
  86 /* kgdb console driver is loaded */
  87 static int kgdb_con_registered;
  88 /* determine if kgdb console output should be used */
  89 static int kgdb_use_con;
  90 /* Flag for alternate operations for early debugging */
  91 bool dbg_is_early = true;
  92 /* Next cpu to become the master debug core */
  93 int dbg_switch_cpu;
  94
  95 /* Use kdb or gdbserver mode */
  96 int dbg_kdb_mode = 1;
  97
  98 static int __init opt_kgdb_con(char *str)
  99 {
 100         kgdb_use_con = 1;
 101         return 0;
 102 }
 103
 104 early_param("kgdbcon", opt_kgdb_con);
 105
 106 module_param(kgdb_use_con, int, 0644);
 107 module_param(kgdbreboot, int, 0644);
 108
 109 /*
 110  * Holds information about breakpoints in a kernel. These breakpoints are
 111  * added and removed by gdb.
 112  */
 113 static struct kgdb_bkpt         kgdb_break[KGDB_MAX_BREAKPOINTS] = {
 114         [0 ... KGDB_MAX_BREAKPOINTS-1] = { .state = BP_UNDEFINED }
 115 };
 116
 117 /*
 118  * The CPU# of the active CPU, or -1 if none:
 119  */
 120 atomic_t                        kgdb_active = ATOMIC_INIT(-1);
 121 EXPORT_SYMBOL_GPL(kgdb_active);
 122 static DEFINE_RAW_SPINLOCK(dbg_master_lock);
 123 static DEFINE_RAW_SPINLOCK(dbg_slave_lock);
 124
 125 /*
 126  * We use NR_CPUs not PERCPU, in case kgdb is used to debug early
 127  * bootup code (which might not have percpu set up yet):
 128  */
 129 static atomic_t                 masters_in_kgdb;
 130 static atomic_t                 slaves_in_kgdb;
 131 static atomic_t                 kgdb_break_tasklet_var;
 132 atomic_t                        kgdb_setting_breakpoint;
 133
 134 struct task_struct              *kgdb_usethread;
 135 struct task_struct              *kgdb_contthread;
 136
 137 int                             kgdb_single_step;
 138 static pid_t                    kgdb_sstep_pid;
 139
 140 /* to keep track of the CPU which is doing the single stepping*/
 141 atomic_t                        kgdb_cpu_doing_single_step = ATOMIC_INIT(-1);
 142
 143 /*
 144  * If you are debugging a problem where roundup (the collection of
 145  * all other CPUs) is a problem [this should be extremely rare],
 146  * then use the nokgdbroundup option to avoid roundup. In that case
 147  * the other CPUs might interfere with your debugging context, so
 148  * use this with care:
 149  */
 150 static int kgdb_do_roundup = 1;
 151
 152 static int __init opt_nokgdbroundup(char *str)
 153 {
 154         kgdb_do_roundup = 0;
 155
 156         return 0;
 157 }
 158
 159 early_param("nokgdbroundup", opt_nokgdbroundup);
 160
 161 /*
 162  * Finally, some KGDB code :-)
 163  */
 164
 165 /*
 166  * Weak aliases for breakpoint management,
 167  * can be overriden by architectures when needed:
 168  */
 169 int __weak kgdb_arch_set_breakpoint(struct kgdb_bkpt *bpt)
 170 {
 171         int err;
 172
 173         err = probe_kernel_read(bpt->saved_instr, (char *)bpt->bpt_addr,
 174                                 BREAK_INSTR_SIZE);
 175         if (err)
 176                 return err;
 177         err = probe_kernel_write((char *)bpt->bpt_addr,
 178                                  arch_kgdb_ops.gdb_bpt_instr, BREAK_INSTR_SIZE);
 179         return err;
 180 }
 181
 182 int __weak kgdb_arch_remove_breakpoint(struct kgdb_bkpt *bpt)
 183 {
 184         return probe_kernel_write((char *)bpt->bpt_addr,
 185                                   (char *)bpt->saved_instr, BREAK_INSTR_SIZE);
 186 }
 187
 188 int __weak kgdb_validate_break_address(unsigned long addr)
 189 {
 190         struct kgdb_bkpt tmp;
 191         int err;
 192         /* Validate setting the breakpoint and then removing it.  If the
 193          * remove fails, the kernel needs to emit a bad message because we
 194          * are deep trouble not being able to put things back the way we
 195          * found them.
 196          */
 197         tmp.bpt_addr = addr;
 198         err = kgdb_arch_set_breakpoint(&tmp);
 199         if (err)
 200                 return err;
 201         err = kgdb_arch_remove_breakpoint(&tmp);
 202         if (err)
 203                 pr_err("Critical breakpoint error, kernel memory destroyed at: %lx\n",
 204                        addr);
 205         return err;
 206 }
 207
 208 unsigned long __weak kgdb_arch_pc(int exception, struct pt_regs *regs)
 209 {
 210         return instruction_pointer(regs);
 211 }
 212
 213 int __weak kgdb_arch_init(void)
 214 {
 215         return 0;
 216 }
 217
 218 int __weak kgdb_skipexception(int exception, struct pt_regs *regs)
 219 {
 220         return 0;
 221 }
 222
 223 /*
 224  * Some architectures need cache flushes when we set/clear a
 225  * breakpoint:
 226  */
 227 static void kgdb_flush_swbreak_addr(unsigned long addr)
 228 {
 229         if (!CACHE_FLUSH_IS_SAFE)
 230                 return;
 231
 232         if (current->mm) {
 233                 int i;
 234
 235                 for (i = 0; i < VMACACHE_SIZE; i++) {
 236                         if (!current->vmacache.vmas[i])
 237                                 continue;
 238                         flush_cache_range(current->vmacache.vmas[i],
 239                                           addr, addr + BREAK_INSTR_SIZE);
 240                 }
 241         }
 242
 243         /* Force flush instruction cache if it was outside the mm */
 244         flush_icache_range(addr, addr + BREAK_INSTR_SIZE);
 245 }
 246
 247 /*
 248  * SW breakpoint management:
 249  */
 250 int dbg_activate_sw_breakpoints(void)
 251 {
 252         int error;
 253         int ret = 0;
 254         int i;
 255
 256         for (i = 0; i < KGDB_MAX_BREAKPOINTS; i++) {
 257                 if (kgdb_break[i].state != BP_SET)
 258                         continue;
 259
 260                 error = kgdb_arch_set_breakpoint(&kgdb_break[i]);
 261                 if (error) {
 262                         ret = error;
 263                         pr_info("BP install failed: %lx\n",
 264                                 kgdb_break[i].bpt_addr);
 265                         continue;
 266                 }
 267
 268                 kgdb_flush_swbreak_addr(kgdb_break[i].bpt_addr);
 269                 kgdb_break[i].state = BP_ACTIVE;
 270         }
 271         return ret;
 272 }
 273
 274 int dbg_set_sw_break(unsigned long addr)
 275 {
 276         int err = kgdb_validate_break_address(addr);
 277         int breakno = -1;
 278         int i;
 279
 280         if (err)
 281                 return err;
 282
 283         for (i = 0; i < KGDB_MAX_BREAKPOINTS; i++) {
 284                 if ((kgdb_break[i].state == BP_SET) &&
 285                                         (kgdb_break[i].bpt_addr == addr))
 286                         return -EEXIST;
 287         }
 288         for (i = 0; i < KGDB_MAX_BREAKPOINTS; i++) {
 289                 if (kgdb_break[i].state == BP_REMOVED &&
 290                                         kgdb_break[i].bpt_addr == addr) {
 291                         breakno = i;
 292                         break;
 293                 }
 294         }
 295
 296         if (breakno == -1) {
 297                 for (i = 0; i < KGDB_MAX_BREAKPOINTS; i++) {
 298                         if (kgdb_break[i].state == BP_UNDEFINED) {
 299                                 breakno = i;
 300                                 break;
 301                         }
 302                 }
 303         }
 304
 305         if (breakno == -1)
 306                 return -E2BIG;
 307
 308         kgdb_break[breakno].state = BP_SET;
 309         kgdb_break[breakno].type = BP_BREAKPOINT;
 310         kgdb_break[breakno].bpt_addr = addr;
 311
 312         return 0;
 313 }
 314
 315 int dbg_deactivate_sw_breakpoints(void)
 316 {
 317         int error;
 318         int ret = 0;
 319         int i;
 320
 321         for (i = 0; i < KGDB_MAX_BREAKPOINTS; i++) {
 322                 if (kgdb_break[i].state != BP_ACTIVE)
 323                         continue;
 324                 error = kgdb_arch_remove_breakpoint(&kgdb_break[i]);
 325                 if (error) {
 326                         pr_info("BP remove failed: %lx\n",
 327                                 kgdb_break[i].bpt_addr);
 328                         ret = error;
 329                 }
 330
 331                 kgdb_flush_swbreak_addr(kgdb_break[i].bpt_addr);
 332                 kgdb_break[i].state = BP_SET;
 333         }
 334         return ret;
 335 }
 336
 337 int dbg_remove_sw_break(unsigned long addr)
 338 {
 339         int i;
 340
 341         for (i = 0; i < KGDB_MAX_BREAKPOINTS; i++) {
 342                 if ((kgdb_break[i].state == BP_SET) &&
 343                                 (kgdb_break[i].bpt_addr == addr)) {
 344                         kgdb_break[i].state = BP_REMOVED;
 345                         return 0;
 346                 }
 347         }
 348         return -ENOENT;
 349 }
 350
 351 int kgdb_isremovedbreak(unsigned long addr)
 352 {
 353         int i;
 354
 355         for (i = 0; i < KGDB_MAX_BREAKPOINTS; i++) {
 356                 if ((kgdb_break[i].state == BP_REMOVED) &&
 357                                         (kgdb_break[i].bpt_addr == addr))
 358                         return 1;
 359         }
 360         return 0;
 361 }
 362
 363 int dbg_remove_all_break(void)
 364 {
 365         int error;
 366         int i;
 367
 368         /* Clear memory breakpoints. */
 369         for (i = 0; i < KGDB_MAX_BREAKPOINTS; i++) {
 370                 if (kgdb_break[i].state != BP_ACTIVE)
 371                         goto setundefined;
 372                 error = kgdb_arch_remove_breakpoint(&kgdb_break[i]);
 373                 if (error)
 374                         pr_err("breakpoint remove failed: %lx\n",
 375                                kgdb_break[i].bpt_addr);
 376 setundefined:
 377                 kgdb_break[i].state = BP_UNDEFINED;
 378         }
 379
 380         /* Clear hardware breakpoints. */
 381         if (arch_kgdb_ops.remove_all_hw_break)
 382                 arch_kgdb_ops.remove_all_hw_break();
 383
 384         return 0;
 385 }
 386
 387 /*
 388  * Return true if there is a valid kgdb I/O module.  Also if no
 389  * debugger is attached a message can be printed to the console about
 390  * waiting for the debugger to attach.
 391  *
 392  * The print_wait argument is only to be true when called from inside
 393  * the core kgdb_handle_exception, because it will wait for the
 394  * debugger to attach.
 395  */
 396 static int kgdb_io_ready(int print_wait)
 397 {
 398         if (!dbg_io_ops)
 399                 return 0;
 400         if (kgdb_connected)
 401                 return 1;
 402         if (atomic_read(&kgdb_setting_breakpoint))
 403                 return 1;
 404         if (print_wait) {
 405 #ifdef CONFIG_KGDB_KDB
 406                 if (!dbg_kdb_mode)
 407                         pr_crit("waiting... or $3#33 for KDB\n");
 408 #else
 409                 pr_crit("Waiting for remote debugger\n");
 410 #endif
 411         }
 412         return 1;
 413 }
 414
 415 static int kgdb_reenter_check(struct kgdb_state *ks)
 416 {
 417         unsigned long addr;
 418
 419         if (atomic_read(&kgdb_active) != raw_smp_processor_id())
 420                 return 0;
 421
 422         /* Panic on recursive debugger calls: */
 423         exception_level++;
 424         addr = kgdb_arch_pc(ks->ex_vector, ks->linux_regs);
 425         dbg_deactivate_sw_breakpoints();
 426
 427         /*
 428          * If the break point removed ok at the place exception
 429          * occurred, try to recover and print a warning to the end
 430          * user because the user planted a breakpoint in a place that
 431          * KGDB needs in order to function.
 432          */
 433         if (dbg_remove_sw_break(addr) == 0) {
 434                 exception_level = 0;
 435                 kgdb_skipexception(ks->ex_vector, ks->linux_regs);
 436                 dbg_activate_sw_breakpoints();
 437                 pr_crit("re-enter error: breakpoint removed %lx\n", addr);
 438                 WARN_ON_ONCE(1);
 439
 440                 return 1;
 441         }
 442         dbg_remove_all_break();
 443         kgdb_skipexception(ks->ex_vector, ks->linux_regs);
 444
 445         if (exception_level > 1) {
 446                 dump_stack();
 447                 panic("Recursive entry to debugger");
 448         }
 449
 450         pr_crit("re-enter exception: ALL breakpoints killed\n");
 451 #ifdef CONFIG_KGDB_KDB
 452         /* Allow kdb to debug itself one level */
 453         return 0;
 454 #endif
 455         dump_stack();
 456         panic("Recursive entry to debugger");
 457
 458         return 1;
 459 }
 460
 461 static void dbg_touch_watchdogs(void)
 462 {
 463         touch_softlockup_watchdog_sync();
 464         clocksource_touch_watchdog();
 465         rcu_cpu_stall_reset();
 466 }
 467
 468 static int kgdb_cpu_enter(struct kgdb_state *ks, struct pt_regs *regs,
 469                 int exception_state)
 470 {
 471         unsigned long flags;
 472         int sstep_tries = 100;
 473         int error;
 474         int cpu;
 475         int trace_on = 0;
 476         int online_cpus = num_online_cpus();
 477         u64 time_left;
 478
 479         kgdb_info[ks->cpu].enter_kgdb++;
 480         kgdb_info[ks->cpu].exception_state |= exception_state;
 481
 482         if (exception_state == DCPU_WANT_MASTER)
 483                 atomic_inc(&masters_in_kgdb);
 484         else
 485                 atomic_inc(&slaves_in_kgdb);
 486
 487         if (arch_kgdb_ops.disable_hw_break)
 488                 arch_kgdb_ops.disable_hw_break(regs);
 489
 490 acquirelock:
 491         /*
 492          * Interrupts will be restored by the 'trap return' code, except when
 493          * single stepping.
 494          */
 495         local_irq_save(flags);
 496
 497         cpu = ks->cpu;
 498         kgdb_info[cpu].debuggerinfo = regs;
 499         kgdb_info[cpu].task = current;
 500         kgdb_info[cpu].ret_state = 0;
 501         kgdb_info[cpu].irq_depth = hardirq_count() >> HARDIRQ_SHIFT;
 502
 503         /* Make sure the above info reaches the primary CPU */
 504         smp_mb();
 505
 506         if (exception_level == 1) {
 507                 if (raw_spin_trylock(&dbg_master_lock))
 508                         atomic_xchg(&kgdb_active, cpu);
 509                 goto cpu_master_loop;
 510         }
 511
 512         /*
 513          * CPU will loop if it is a slave or request to become a kgdb
 514          * master cpu and acquire the kgdb_active lock:
 515          */
 516         while (1) {
 517 cpu_loop:
 518                 if (kgdb_info[cpu].exception_state & DCPU_NEXT_MASTER) {
 519                         kgdb_info[cpu].exception_state &= ~DCPU_NEXT_MASTER;
 520                         goto cpu_master_loop;
 521                 } else if (kgdb_info[cpu].exception_state & DCPU_WANT_MASTER) {
 522                         if (raw_spin_trylock(&dbg_master_lock)) {
 523                                 atomic_xchg(&kgdb_active, cpu);
 524                                 break;
 525                         }
 526                 } else if (kgdb_info[cpu].exception_state & DCPU_IS_SLAVE) {
 527                         if (!raw_spin_is_locked(&dbg_slave_lock))
 528                                 goto return_normal;
 529                 } else {
 530 return_normal:
 531                         /* Return to normal operation by executing any
 532                          * hw breakpoint fixup.
 533                          */
 534                         if (arch_kgdb_ops.correct_hw_break)
 535                                 arch_kgdb_ops.correct_hw_break();
 536                         if (trace_on)
 537                                 tracing_on();
 538                         kgdb_info[cpu].exception_state &=
 539                                 ~(DCPU_WANT_MASTER | DCPU_IS_SLAVE);
 540                         kgdb_info[cpu].enter_kgdb--;
 541                         smp_mb__before_atomic();
 542                         atomic_dec(&slaves_in_kgdb);
 543                         dbg_touch_watchdogs();
 544                         local_irq_restore(flags);
 545                         return 0;
 546                 }
 547                 cpu_relax();
 548         }
 549
 550         /*
 551          * For single stepping, try to only enter on the processor
 552          * that was single stepping.  To guard against a deadlock, the
 553          * kernel will only try for the value of sstep_tries before
 554          * giving up and continuing on.
 555          */
 556         if (atomic_read(&kgdb_cpu_doing_single_step) != -1 &&
 557             (kgdb_info[cpu].task &&
 558              kgdb_info[cpu].task->pid != kgdb_sstep_pid) && --sstep_tries) {
 559                 atomic_set(&kgdb_active, -1);
 560                 raw_spin_unlock(&dbg_master_lock);
 561                 dbg_touch_watchdogs();
 562                 local_irq_restore(flags);
 563
 564                 goto acquirelock;
 565         }
 566
 567         if (!kgdb_io_ready(1)) {
 568                 kgdb_info[cpu].ret_state = 1;
 569                 goto kgdb_restore; /* No I/O connection, resume the system */
 570         }
 571
 572         /*
 573          * Don't enter if we have hit a removed breakpoint.
 574          */
 575         if (kgdb_skipexception(ks->ex_vector, ks->linux_regs))
 576                 goto kgdb_restore;
 577
 578         /* Call the I/O driver's pre_exception routine */
 579         if (dbg_io_ops->pre_exception)
 580                 dbg_io_ops->pre_exception();
 581
 582         /*
 583          * Get the passive CPU lock which will hold all the non-primary
 584          * CPU in a spin state while the debugger is active
 585          */
 586         if (!kgdb_single_step)
 587                 raw_spin_lock(&dbg_slave_lock);
 588
 589 #ifdef CONFIG_SMP
 590         /* If send_ready set, slaves are already waiting */
 591         if (ks->send_ready)
 592                 atomic_set(ks->send_ready, 1);
 593
 594         /* Signal the other CPUs to enter kgdb_wait() */
 595         else if ((!kgdb_single_step) && kgdb_do_roundup)
 596                 kgdb_roundup_cpus(flags);
 597 #endif
 598
 599         /*
 600          * Wait for the other CPUs to be notified and be waiting for us:
 601          */
 602         time_left = MSEC_PER_SEC;
 603         while (kgdb_do_roundup && --time_left &&
 604                (atomic_read(&masters_in_kgdb) + atomic_read(&slaves_in_kgdb)) !=
 605                    online_cpus)
 606                 udelay(1000);
 607         if (!time_left)
 608                 pr_crit("Timed out waiting for secondary CPUs.\n");
 609
 610         /*
 611          * At this point the primary processor is completely
 612          * in the debugger and all secondary CPUs are quiescent
 613          */
 614         dbg_deactivate_sw_breakpoints();
 615         kgdb_single_step = 0;
 616         kgdb_contthread = current;
 617         exception_level = 0;
 618         trace_on = tracing_is_on();
 619         if (trace_on)
 620                 tracing_off();
 621
 622         while (1) {
 623 cpu_master_loop:
 624                 if (dbg_kdb_mode) {
 625                         kgdb_connected = 1;
 626                         error = kdb_stub(ks);
 627                         if (error == -1)
 628                                 continue;
 629                         kgdb_connected = 0;
 630                 } else {
 631                         error = gdb_serial_stub(ks);
 632                 }
 633
 634                 if (error == DBG_PASS_EVENT) {
 635                         dbg_kdb_mode = !dbg_kdb_mode;
 636                 } else if (error == DBG_SWITCH_CPU_EVENT) {
 637                         kgdb_info[dbg_switch_cpu].exception_state |=
 638                                 DCPU_NEXT_MASTER;
 639                         goto cpu_loop;
 640                 } else {
 641                         kgdb_info[cpu].ret_state = error;
 642                         break;
 643                 }
 644         }
 645
 646         /* Call the I/O driver's post_exception routine */
 647         if (dbg_io_ops->post_exception)
 648                 dbg_io_ops->post_exception();
 649
 650         if (!kgdb_single_step) {
 651                 raw_spin_unlock(&dbg_slave_lock);
 652                 /* Wait till all the CPUs have quit from the debugger. */
 653                 while (kgdb_do_roundup && atomic_read(&slaves_in_kgdb))
 654                         cpu_relax();
 655         }
 656
 657 kgdb_restore:
 658         if (atomic_read(&kgdb_cpu_doing_single_step) != -1) {
 659                 int sstep_cpu = atomic_read(&kgdb_cpu_doing_single_step);
 660                 if (kgdb_info[sstep_cpu].task)
 661                         kgdb_sstep_pid = kgdb_info[sstep_cpu].task->pid;
 662                 else
 663                         kgdb_sstep_pid = 0;
 664         }
 665         if (arch_kgdb_ops.correct_hw_break)
 666                 arch_kgdb_ops.correct_hw_break();
 667         if (trace_on)
 668                 tracing_on();
 669
 670         kgdb_info[cpu].exception_state &=
 671                 ~(DCPU_WANT_MASTER | DCPU_IS_SLAVE);
 672         kgdb_info[cpu].enter_kgdb--;
 673         smp_mb__before_atomic();
 674         atomic_dec(&masters_in_kgdb);
 675         /* Free kgdb_active */
 676         atomic_set(&kgdb_active, -1);
 677         raw_spin_unlock(&dbg_master_lock);
 678         dbg_touch_watchdogs();
 679         local_irq_restore(flags);
 680
 681         return kgdb_info[cpu].ret_state;
 682 }
 683
 684 /*
 685  * kgdb_handle_exception() - main entry point from a kernel exception
 686  *
 687  * Locking hierarchy:
 688  *      interface locks, if any (begin_session)
 689  *      kgdb lock (kgdb_active)
 690  */
 691 int
 692 kgdb_handle_exception(int evector, int signo, int ecode, struct pt_regs *regs)
 693 {
 694         struct kgdb_state kgdb_var;
 695         struct kgdb_state *ks = &kgdb_var;
 696         int ret = 0;
 697
 698         if (arch_kgdb_ops.enable_nmi)
 699                 arch_kgdb_ops.enable_nmi(0);
 700         /*
 701          * Avoid entering the debugger if we were triggered due to an oops
 702          * but panic_timeout indicates the system should automatically
 703          * reboot on panic. We don't want to get stuck waiting for input
 704          * on such systems, especially if its "just" an oops.
 705          */
 706         if (signo != SIGTRAP && panic_timeout)
 707                 return 1;
 708
 709         memset(ks, 0, sizeof(struct kgdb_state));
 710         ks->cpu                 = raw_smp_processor_id();
 711         ks->ex_vector           = evector;
 712         ks->signo               = signo;
 713         ks->err_code            = ecode;
 714         ks->linux_regs          = regs;
 715
 716         if (kgdb_reenter_check(ks))
 717                 goto out; /* Ouch, double exception ! */
 718         if (kgdb_info[ks->cpu].enter_kgdb != 0)
 719                 goto out;
 720
 721         ret = kgdb_cpu_enter(ks, regs, DCPU_WANT_MASTER);
 722 out:
 723         if (arch_kgdb_ops.enable_nmi)
 724                 arch_kgdb_ops.enable_nmi(1);
 725         return ret;
 726 }
 727
 728 /*
 729  * GDB places a breakpoint at this function to know dynamically
 730  * loaded objects. It's not defined static so that only one instance with this
 731  * name exists in the kernel.
 732  */
 733
 734 static int module_event(struct notifier_block *self, unsigned long val,
 735         void *data)
 736 {
 737         return 0;
 738 }
 739
 740 static struct notifier_block dbg_module_load_nb = {
 741         .notifier_call  = module_event,
 742 };
 743
 744 int kgdb_nmicallback(int cpu, void *regs)
 745 {
 746 #ifdef CONFIG_SMP
 747         struct kgdb_state kgdb_var;
 748         struct kgdb_state *ks = &kgdb_var;
 749
 750         memset(ks, 0, sizeof(struct kgdb_state));
 751         ks->cpu                 = cpu;
 752         ks->linux_regs          = regs;
 753
 754         if (kgdb_info[ks->cpu].enter_kgdb == 0 &&
 755                         raw_spin_is_locked(&dbg_master_lock)) {
 756                 kgdb_cpu_enter(ks, regs, DCPU_IS_SLAVE);
 757                 return 0;
 758         }
 759 #endif
 760         return 1;
 761 }
 762
 763 int kgdb_nmicallin(int cpu, int trapnr, void *regs, int err_code,
 764                                                         atomic_t *send_ready)
 765 {
 766 #ifdef CONFIG_SMP
 767         if (!kgdb_io_ready(0) || !send_ready)
 768                 return 1;
 769
 770         if (kgdb_info[cpu].enter_kgdb == 0) {
 771                 struct kgdb_state kgdb_var;
 772                 struct kgdb_state *ks = &kgdb_var;
 773
 774                 memset(ks, 0, sizeof(struct kgdb_state));
 775                 ks->cpu                 = cpu;
 776                 ks->ex_vector           = trapnr;
 777                 ks->signo               = SIGTRAP;
 778                 ks->err_code            = err_code;
 779                 ks->linux_regs          = regs;
 780                 ks->send_ready          = send_ready;
 781                 kgdb_cpu_enter(ks, regs, DCPU_WANT_MASTER);
 782                 return 0;
 783         }
 784 #endif
 785         return 1;
 786 }
 787
 788 static void kgdb_console_write(struct console *co, const char *s,
 789    unsigned count)
 790 {
 791         unsigned long flags;
 792
 793         /* If we're debugging, or KGDB has not connected, don't try
 794          * and print. */
 795         if (!kgdb_connected || atomic_read(&kgdb_active) != -1 || dbg_kdb_mode)
 796                 return;
 797
 798         local_irq_save(flags);
 799         gdbstub_msg_write(s, count);
 800         local_irq_restore(flags);
 801 }
 802
 803 static struct console kgdbcons = {
 804         .name           = "kgdb",
 805         .write          = kgdb_console_write,
 806         .flags          = CON_PRINTBUFFER | CON_ENABLED,
 807         .index          = -1,
 808 };
 809
 810 #ifdef CONFIG_MAGIC_SYSRQ
 811 static void sysrq_handle_dbg(int key)
 812 {
 813         if (!dbg_io_ops) {
 814                 pr_crit("ERROR: No KGDB I/O module available\n");
 815                 return;
 816         }
 817         if (!kgdb_connected) {
 818 #ifdef CONFIG_KGDB_KDB
 819                 if (!dbg_kdb_mode)
 820                         pr_crit("KGDB or $3#33 for KDB\n");
 821 #else
 822                 pr_crit("Entering KGDB\n");
 823 #endif
 824         }
 825
 826         kgdb_breakpoint();
 827 }
 828
 829 static struct sysrq_key_op sysrq_dbg_op = {
 830         .handler        = sysrq_handle_dbg,
 831         .help_msg       = "debug(g)",
 832         .action_msg     = "DEBUG",
 833 };
 834 #endif
 835
 836 static int kgdb_panic_event(struct notifier_block *self,
 837                             unsigned long val,
 838                             void *data)
 839 {
 840         /*
 841          * Avoid entering the debugger if we were triggered due to a panic
 842          * We don't want to get stuck waiting for input from user in such case.
 843          * panic_timeout indicates the system should automatically
 844          * reboot on panic.
 845          */
 846         if (panic_timeout)
 847                 return NOTIFY_DONE;
 848
 849         if (dbg_kdb_mode)
 850                 kdb_printf("PANIC: %s\n", (char *)data);
 851         kgdb_breakpoint();
 852         return NOTIFY_DONE;
 853 }
 854
 855 static struct notifier_block kgdb_panic_event_nb = {
 856        .notifier_call   = kgdb_panic_event,
 857        .priority        = INT_MAX,
 858 };
 859
 860 void __weak kgdb_arch_late(void)
 861 {
 862 }
 863
 864 void __init dbg_late_init(void)
 865 {
 866         dbg_is_early = false;
 867         if (kgdb_io_module_registered)
 868                 kgdb_arch_late();
 869         kdb_init(KDB_INIT_FULL);
 870 }
 871
 872 static int
 873 dbg_notify_reboot(struct notifier_block *this, unsigned long code, void *x)
 874 {
 875         /*
 876          * Take the following action on reboot notify depending on value:
 877          *    1 == Enter debugger
 878          *    0 == [the default] detatch debug client
 879          *   -1 == Do nothing... and use this until the board resets
 880          */
 881         switch (kgdbreboot) {
 882         case 1:
 883                 kgdb_breakpoint();
 884         case -1:
 885                 goto done;
 886         }
 887         if (!dbg_kdb_mode)
 888                 gdbstub_exit(code);
 889 done:
 890         return NOTIFY_DONE;
 891 }
 892
 893 static struct notifier_block dbg_reboot_notifier = {
 894         .notifier_call          = dbg_notify_reboot,
 895         .next                   = NULL,
 896         .priority               = INT_MAX,
 897 };
 898
 899 static void kgdb_register_callbacks(void)
 900 {
 901         if (!kgdb_io_module_registered) {
 902                 kgdb_io_module_registered = 1;
 903                 kgdb_arch_init();
 904                 if (!dbg_is_early)
 905                         kgdb_arch_late();
 906                 register_module_notifier(&dbg_module_load_nb);
 907                 register_reboot_notifier(&dbg_reboot_notifier);
 908                 atomic_notifier_chain_register(&panic_notifier_list,
 909                                                &kgdb_panic_event_nb);
 910 #ifdef CONFIG_MAGIC_SYSRQ
 911                 register_sysrq_key('g', &sysrq_dbg_op);
 912 #endif
 913                 if (kgdb_use_con && !kgdb_con_registered) {
 914                         register_console(&kgdbcons);
 915                         kgdb_con_registered = 1;
 916                 }
 917         }
 918 }
 919
 920 static void kgdb_unregister_callbacks(void)
 921 {
 922         /*
 923          * When this routine is called KGDB should unregister from the
 924          * panic handler and clean up, making sure it is not handling any
 925          * break exceptions at the time.
 926          */
 927         if (kgdb_io_module_registered) {
 928                 kgdb_io_module_registered = 0;
 929                 unregister_reboot_notifier(&dbg_reboot_notifier);
 930                 unregister_module_notifier(&dbg_module_load_nb);
 931                 atomic_notifier_chain_unregister(&panic_notifier_list,
 932                                                &kgdb_panic_event_nb);
 933                 kgdb_arch_exit();
 934 #ifdef CONFIG_MAGIC_SYSRQ
 935                 unregister_sysrq_key('g', &sysrq_dbg_op);
 936 #endif
 937                 if (kgdb_con_registered) {
 938                         unregister_console(&kgdbcons);
 939                         kgdb_con_registered = 0;
 940                 }
 941         }
 942 }
 943
 944 /*
 945  * There are times a tasklet needs to be used vs a compiled in
 946  * break point so as to cause an exception outside a kgdb I/O module,
 947  * such as is the case with kgdboe, where calling a breakpoint in the
 948  * I/O driver itself would be fatal.
 949  */
 950 static void kgdb_tasklet_bpt(unsigned long ing)
 951 {
 952         kgdb_breakpoint();
 953         atomic_set(&kgdb_break_tasklet_var, 0);
 954 }
 955
 956 static DECLARE_TASKLET(kgdb_tasklet_breakpoint, kgdb_tasklet_bpt, 0);
 957
 958 void kgdb_schedule_breakpoint(void)
 959 {
 960         if (atomic_read(&kgdb_break_tasklet_var) ||
 961                 atomic_read(&kgdb_active) != -1 ||
 962                 atomic_read(&kgdb_setting_breakpoint))
 963                 return;
 964         atomic_inc(&kgdb_break_tasklet_var);
 965         tasklet_schedule(&kgdb_tasklet_breakpoint);
 966 }
 967 EXPORT_SYMBOL_GPL(kgdb_schedule_breakpoint);
 968
 969 static void kgdb_initial_breakpoint(void)
 970 {
 971         kgdb_break_asap = 0;
 972
 973         pr_crit("Waiting for connection from remote gdb...\n");
 974         kgdb_breakpoint();
 975 }
 976
 977 /**
 978  *      kgdb_register_io_module - register KGDB IO module
 979  *      @new_dbg_io_ops: the io ops vector
 980  *
 981  *      Register it with the KGDB core.
 982  */
 983 int kgdb_register_io_module(struct kgdb_io *new_dbg_io_ops)
 984 {
 985         int err;
 986
 987         spin_lock(&kgdb_registration_lock);
 988
 989         if (dbg_io_ops) {
 990                 spin_unlock(&kgdb_registration_lock);
 991
 992                 pr_err("Another I/O driver is already registered with KGDB\n");
 993                 return -EBUSY;
 994         }
 995
 996         if (new_dbg_io_ops->init) {
 997                 err = new_dbg_io_ops->init();
 998                 if (err) {
 999                         spin_unlock(&kgdb_registration_lock);
1000                         return err;
1001                 }
1002         }
1003
1004         dbg_io_ops = new_dbg_io_ops;
1005
1006         spin_unlock(&kgdb_registration_lock);
1007
1008         pr_info("Registered I/O driver %s\n", new_dbg_io_ops->name);
1009
1010         /* Arm KGDB now. */
1011         kgdb_register_callbacks();
1012
1013         if (kgdb_break_asap)
1014                 kgdb_initial_breakpoint();
1015
1016         return 0;
1017 }
1018 EXPORT_SYMBOL_GPL(kgdb_register_io_module);
1019
1020 /**
1021  *      kkgdb_unregister_io_module - unregister KGDB IO module
1022  *      @old_dbg_io_ops: the io ops vector
1023  *
1024  *      Unregister it with the KGDB core.
1025  */
1026 void kgdb_unregister_io_module(struct kgdb_io *old_dbg_io_ops)
1027 {
1028         BUG_ON(kgdb_connected);
1029
1030         /*
1031          * KGDB is no longer able to communicate out, so
1032          * unregister our callbacks and reset state.
1033          */
1034         kgdb_unregister_callbacks();
1035
1036         spin_lock(&kgdb_registration_lock);
1037
1038         WARN_ON_ONCE(dbg_io_ops != old_dbg_io_ops);
1039         dbg_io_ops = NULL;
1040
1041         spin_unlock(&kgdb_registration_lock);
1042
1043         pr_info("Unregistered I/O driver %s, debugger disabled\n",
1044                 old_dbg_io_ops->name);
1045 }
1046 EXPORT_SYMBOL_GPL(kgdb_unregister_io_module);
1047
1048 int dbg_io_get_char(void)
1049 {
1050         int ret = dbg_io_ops->read_char();
1051         if (ret == NO_POLL_CHAR)
1052                 return -1;
1053         if (!dbg_kdb_mode)
1054                 return ret;
1055         if (ret == 127)
1056                 return 8;
1057         return ret;
1058 }
1059
1060 /**
1061  * kgdb_breakpoint - generate breakpoint exception
1062  *
1063  * This function will generate a breakpoint exception.  It is used at the
1064  * beginning of a program to sync up with a debugger and can be used
1065  * otherwise as a quick means to stop program execution and "break" into
1066  * the debugger.
1067  */
1068 noinline void kgdb_breakpoint(void)
1069 {
1070         atomic_inc(&kgdb_setting_breakpoint);
1071         wmb(); /* Sync point before breakpoint */
1072         arch_kgdb_breakpoint();
1073         wmb(); /* Sync point after breakpoint */
1074         atomic_dec(&kgdb_setting_breakpoint);
1075 }
1076 EXPORT_SYMBOL_GPL(kgdb_breakpoint);
1077
1078 static int __init opt_kgdb_wait(char *str)
1079 {
1080         kgdb_break_asap = 1;
1081
1082         kdb_init(KDB_INIT_EARLY);
1083         if (kgdb_io_module_registered)
1084                 kgdb_initial_breakpoint();
1085
1086         return 0;
1087 }
1088
1089 early_param("kgdbwait", opt_kgdb_wait);