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/pid.h>
  53 #include <linux/smp.h>
  54 #include <linux/mm.h>
  55 #include <linux/vmacache.h>
  56 #include <linux/rcupdate.h>
  57
  58 #include <asm/cacheflush.h>
  59 #include <asm/byteorder.h>
  60 #include <linux/atomic.h>
  61
  62 #include "debug_core.h"
  63
  64 static int kgdb_break_asap;
  65
  66 struct debuggerinfo_struct kgdb_info[NR_CPUS];
  67
  68 /**
  69  * kgdb_connected - Is a host GDB connected to us?
  70  */
  71 int                             kgdb_connected;
  72 EXPORT_SYMBOL_GPL(kgdb_connected);
  73
  74 /* All the KGDB handlers are installed */
  75 int                     kgdb_io_module_registered;
  76
  77 /* Guard for recursive entry */
  78 static int                      exception_level;
  79
  80 struct kgdb_io          *dbg_io_ops;
  81 static DEFINE_SPINLOCK(kgdb_registration_lock);
  82
  83 /* Action for the reboot notifiter, a global allow kdb to change it */
  84 static int kgdbreboot;
  85 /* kgdb console driver is loaded */
  86 static int kgdb_con_registered;
  87 /* determine if kgdb console output should be used */
  88 static int kgdb_use_con;
  89 /* Flag for alternate operations for early debugging */
  90 bool dbg_is_early = true;
  91 /* Next cpu to become the master debug core */
  92 int dbg_switch_cpu;
  93
  94 /* Use kdb or gdbserver mode */
  95 int dbg_kdb_mode = 1;
  96
  97 module_param(kgdb_use_con, int, 0644);
  98 module_param(kgdbreboot, int, 0644);
  99
 100 /*
 101  * Holds information about breakpoints in a kernel. These breakpoints are
 102  * added and removed by gdb.
 103  */
 104 static struct kgdb_bkpt         kgdb_break[KGDB_MAX_BREAKPOINTS] = {
 105         [0 ... KGDB_MAX_BREAKPOINTS-1] = { .state = BP_UNDEFINED }
 106 };
 107
 108 /*
 109  * The CPU# of the active CPU, or -1 if none:
 110  */
 111 atomic_t                        kgdb_active = ATOMIC_INIT(-1);
 112 EXPORT_SYMBOL_GPL(kgdb_active);
 113 static DEFINE_RAW_SPINLOCK(dbg_master_lock);
 114 static DEFINE_RAW_SPINLOCK(dbg_slave_lock);
 115
 116 /*
 117  * We use NR_CPUs not PERCPU, in case kgdb is used to debug early
 118  * bootup code (which might not have percpu set up yet):
 119  */
 120 static atomic_t                 masters_in_kgdb;
 121 static atomic_t                 slaves_in_kgdb;
 122 static atomic_t                 kgdb_break_tasklet_var;
 123 atomic_t                        kgdb_setting_breakpoint;
 124
 125 struct task_struct              *kgdb_usethread;
 126 struct task_struct              *kgdb_contthread;
 127
 128 int                             kgdb_single_step;
 129 static pid_t                    kgdb_sstep_pid;
 130
 131 /* to keep track of the CPU which is doing the single stepping*/
 132 atomic_t                        kgdb_cpu_doing_single_step = ATOMIC_INIT(-1);
 133
 134 /*
 135  * If you are debugging a problem where roundup (the collection of
 136  * all other CPUs) is a problem [this should be extremely rare],
 137  * then use the nokgdbroundup option to avoid roundup. In that case
 138  * the other CPUs might interfere with your debugging context, so
 139  * use this with care:
 140  */
 141 static int kgdb_do_roundup = 1;
 142
 143 static int __init opt_nokgdbroundup(char *str)
 144 {
 145         kgdb_do_roundup = 0;
 146
 147         return 0;
 148 }
 149
 150 early_param("nokgdbroundup", opt_nokgdbroundup);
 151
 152 /*
 153  * Finally, some KGDB code :-)
 154  */
 155
 156 /*
 157  * Weak aliases for breakpoint management,
 158  * can be overriden by architectures when needed:
 159  */
 160 int __weak kgdb_arch_set_breakpoint(struct kgdb_bkpt *bpt)
 161 {
 162         int err;
 163
 164         err = probe_kernel_read(bpt->saved_instr, (char *)bpt->bpt_addr,
 165                                 BREAK_INSTR_SIZE);
 166         if (err)
 167                 return err;
 168         err = probe_kernel_write((char *)bpt->bpt_addr,
 169                                  arch_kgdb_ops.gdb_bpt_instr, BREAK_INSTR_SIZE);
 170         return err;
 171 }
 172
 173 int __weak kgdb_arch_remove_breakpoint(struct kgdb_bkpt *bpt)
 174 {
 175         return probe_kernel_write((char *)bpt->bpt_addr,
 176                                   (char *)bpt->saved_instr, BREAK_INSTR_SIZE);
 177 }
 178
 179 int __weak kgdb_validate_break_address(unsigned long addr)
 180 {
 181         struct kgdb_bkpt tmp;
 182         int err;
 183         /* Validate setting the breakpoint and then removing it.  If the
 184          * remove fails, the kernel needs to emit a bad message because we
 185          * are deep trouble not being able to put things back the way we
 186          * found them.
 187          */
 188         tmp.bpt_addr = addr;
 189         err = kgdb_arch_set_breakpoint(&tmp);
 190         if (err)
 191                 return err;
 192         err = kgdb_arch_remove_breakpoint(&tmp);
 193         if (err)
 194                 pr_err("Critical breakpoint error, kernel memory destroyed at: %lx\n",
 195                        addr);
 196         return err;
 197 }
 198
 199 unsigned long __weak kgdb_arch_pc(int exception, struct pt_regs *regs)
 200 {
 201         return instruction_pointer(regs);
 202 }
 203
 204 int __weak kgdb_arch_init(void)
 205 {
 206         return 0;
 207 }
 208
 209 int __weak kgdb_skipexception(int exception, struct pt_regs *regs)
 210 {
 211         return 0;
 212 }
 213
 214 /*
 215  * Some architectures need cache flushes when we set/clear a
 216  * breakpoint:
 217  */
 218 static void kgdb_flush_swbreak_addr(unsigned long addr)
 219 {
 220         if (!CACHE_FLUSH_IS_SAFE)
 221                 return;
 222
 223         if (current->mm) {
 224                 int i;
 225
 226                 for (i = 0; i < VMACACHE_SIZE; i++) {
 227                         if (!current->vmacache[i])
 228                                 continue;
 229                         flush_cache_range(current->vmacache[i],
 230                                           addr, addr + BREAK_INSTR_SIZE);
 231                 }
 232         }
 233
 234         /* Force flush instruction cache if it was outside the mm */
 235         flush_icache_range(addr, addr + BREAK_INSTR_SIZE);
 236 }
 237
 238 /*
 239  * SW breakpoint management:
 240  */
 241 int dbg_activate_sw_breakpoints(void)
 242 {
 243         int error;
 244         int ret = 0;
 245         int i;
 246
 247         for (i = 0; i < KGDB_MAX_BREAKPOINTS; i++) {
 248                 if (kgdb_break[i].state != BP_SET)
 249                         continue;
 250
 251                 error = kgdb_arch_set_breakpoint(&kgdb_break[i]);
 252                 if (error) {
 253                         ret = error;
 254                         pr_info("BP install failed: %lx\n",
 255                                 kgdb_break[i].bpt_addr);
 256                         continue;
 257                 }
 258
 259                 kgdb_flush_swbreak_addr(kgdb_break[i].bpt_addr);
 260                 kgdb_break[i].state = BP_ACTIVE;
 261         }
 262         return ret;
 263 }
 264
 265 int dbg_set_sw_break(unsigned long addr)
 266 {
 267         int err = kgdb_validate_break_address(addr);
 268         int breakno = -1;
 269         int i;
 270
 271         if (err)
 272                 return err;
 273
 274         for (i = 0; i < KGDB_MAX_BREAKPOINTS; i++) {
 275                 if ((kgdb_break[i].state == BP_SET) &&
 276                                         (kgdb_break[i].bpt_addr == addr))
 277                         return -EEXIST;
 278         }
 279         for (i = 0; i < KGDB_MAX_BREAKPOINTS; i++) {
 280                 if (kgdb_break[i].state == BP_REMOVED &&
 281                                         kgdb_break[i].bpt_addr == addr) {
 282                         breakno = i;
 283                         break;
 284                 }
 285         }
 286
 287         if (breakno == -1) {
 288                 for (i = 0; i < KGDB_MAX_BREAKPOINTS; i++) {
 289                         if (kgdb_break[i].state == BP_UNDEFINED) {
 290                                 breakno = i;
 291                                 break;
 292                         }
 293                 }
 294         }
 295
 296         if (breakno == -1)
 297                 return -E2BIG;
 298
 299         kgdb_break[breakno].state = BP_SET;
 300         kgdb_break[breakno].type = BP_BREAKPOINT;
 301         kgdb_break[breakno].bpt_addr = addr;
 302
 303         return 0;
 304 }
 305
 306 int dbg_deactivate_sw_breakpoints(void)
 307 {
 308         int error;
 309         int ret = 0;
 310         int i;
 311
 312         for (i = 0; i < KGDB_MAX_BREAKPOINTS; i++) {
 313                 if (kgdb_break[i].state != BP_ACTIVE)
 314                         continue;
 315                 error = kgdb_arch_remove_breakpoint(&kgdb_break[i]);
 316                 if (error) {
 317                         pr_info("BP remove failed: %lx\n",
 318                                 kgdb_break[i].bpt_addr);
 319                         ret = error;
 320                 }
 321
 322                 kgdb_flush_swbreak_addr(kgdb_break[i].bpt_addr);
 323                 kgdb_break[i].state = BP_SET;
 324         }
 325         return ret;
 326 }
 327
 328 int dbg_remove_sw_break(unsigned long addr)
 329 {
 330         int i;
 331
 332         for (i = 0; i < KGDB_MAX_BREAKPOINTS; i++) {
 333                 if ((kgdb_break[i].state == BP_SET) &&
 334                                 (kgdb_break[i].bpt_addr == addr)) {
 335                         kgdb_break[i].state = BP_REMOVED;
 336                         return 0;
 337                 }
 338         }
 339         return -ENOENT;
 340 }
 341
 342 int kgdb_isremovedbreak(unsigned long addr)
 343 {
 344         int i;
 345
 346         for (i = 0; i < KGDB_MAX_BREAKPOINTS; i++) {
 347                 if ((kgdb_break[i].state == BP_REMOVED) &&
 348                                         (kgdb_break[i].bpt_addr == addr))
 349                         return 1;
 350         }
 351         return 0;
 352 }
 353
 354 int dbg_remove_all_break(void)
 355 {
 356         int error;
 357         int i;
 358
 359         /* Clear memory breakpoints. */
 360         for (i = 0; i < KGDB_MAX_BREAKPOINTS; i++) {
 361                 if (kgdb_break[i].state != BP_ACTIVE)
 362                         goto setundefined;
 363                 error = kgdb_arch_remove_breakpoint(&kgdb_break[i]);
 364                 if (error)
 365                         pr_err("breakpoint remove failed: %lx\n",
 366                                kgdb_break[i].bpt_addr);
 367 setundefined:
 368                 kgdb_break[i].state = BP_UNDEFINED;
 369         }
 370
 371         /* Clear hardware breakpoints. */
 372         if (arch_kgdb_ops.remove_all_hw_break)
 373                 arch_kgdb_ops.remove_all_hw_break();
 374
 375         return 0;
 376 }
 377
 378 /*
 379  * Return true if there is a valid kgdb I/O module.  Also if no
 380  * debugger is attached a message can be printed to the console about
 381  * waiting for the debugger to attach.
 382  *
 383  * The print_wait argument is only to be true when called from inside
 384  * the core kgdb_handle_exception, because it will wait for the
 385  * debugger to attach.
 386  */
 387 static int kgdb_io_ready(int print_wait)
 388 {
 389         if (!dbg_io_ops)
 390                 return 0;
 391         if (kgdb_connected)
 392                 return 1;
 393         if (atomic_read(&kgdb_setting_breakpoint))
 394                 return 1;
 395         if (print_wait) {
 396 #ifdef CONFIG_KGDB_KDB
 397                 if (!dbg_kdb_mode)
 398                         pr_crit("waiting... or $3#33 for KDB\n");
 399 #else
 400                 pr_crit("Waiting for remote debugger\n");
 401 #endif
 402         }
 403         return 1;
 404 }
 405
 406 static int kgdb_reenter_check(struct kgdb_state *ks)
 407 {
 408         unsigned long addr;
 409
 410         if (atomic_read(&kgdb_active) != raw_smp_processor_id())
 411                 return 0;
 412
 413         /* Panic on recursive debugger calls: */
 414         exception_level++;
 415         addr = kgdb_arch_pc(ks->ex_vector, ks->linux_regs);
 416         dbg_deactivate_sw_breakpoints();
 417
 418         /*
 419          * If the break point removed ok at the place exception
 420          * occurred, try to recover and print a warning to the end
 421          * user because the user planted a breakpoint in a place that
 422          * KGDB needs in order to function.
 423          */
 424         if (dbg_remove_sw_break(addr) == 0) {
 425                 exception_level = 0;
 426                 kgdb_skipexception(ks->ex_vector, ks->linux_regs);
 427                 dbg_activate_sw_breakpoints();
 428                 pr_crit("re-enter error: breakpoint removed %lx\n", addr);
 429                 WARN_ON_ONCE(1);
 430
 431                 return 1;
 432         }
 433         dbg_remove_all_break();
 434         kgdb_skipexception(ks->ex_vector, ks->linux_regs);
 435
 436         if (exception_level > 1) {
 437                 dump_stack();
 438                 kgdb_io_module_registered = false;
 439                 panic("Recursive entry to debugger");
 440         }
 441
 442         pr_crit("re-enter exception: ALL breakpoints killed\n");
 443 #ifdef CONFIG_KGDB_KDB
 444         /* Allow kdb to debug itself one level */
 445         return 0;
 446 #endif
 447         dump_stack();
 448         panic("Recursive entry to debugger");
 449
 450         return 1;
 451 }
 452
 453 static void dbg_touch_watchdogs(void)
 454 {
 455         touch_softlockup_watchdog_sync();
 456         clocksource_touch_watchdog();
 457         rcu_cpu_stall_reset();
 458 }
 459
 460 static int kgdb_cpu_enter(struct kgdb_state *ks, struct pt_regs *regs,
 461                 int exception_state)
 462 {
 463         unsigned long flags;
 464         int sstep_tries = 100;
 465         int error;
 466         int cpu;
 467         int trace_on = 0;
 468         int online_cpus = num_online_cpus();
 469         u64 time_left;
 470
 471         kgdb_info[ks->cpu].enter_kgdb++;
 472         kgdb_info[ks->cpu].exception_state |= exception_state;
 473
 474         if (exception_state == DCPU_WANT_MASTER)
 475                 atomic_inc(&masters_in_kgdb);
 476         else
 477                 atomic_inc(&slaves_in_kgdb);
 478
 479         if (arch_kgdb_ops.disable_hw_break)
 480                 arch_kgdb_ops.disable_hw_break(regs);
 481
 482 acquirelock:
 483         rcu_read_lock();
 484         /*
 485          * Interrupts will be restored by the 'trap return' code, except when
 486          * single stepping.
 487          */
 488         local_irq_save(flags);
 489
 490         cpu = ks->cpu;
 491         kgdb_info[cpu].debuggerinfo = regs;
 492         kgdb_info[cpu].task = current;
 493         kgdb_info[cpu].ret_state = 0;
 494         kgdb_info[cpu].irq_depth = hardirq_count() >> HARDIRQ_SHIFT;
 495
 496         /* Make sure the above info reaches the primary CPU */
 497         smp_mb();
 498
 499         if (exception_level == 1) {
 500                 if (raw_spin_trylock(&dbg_master_lock))
 501                         atomic_xchg(&kgdb_active, cpu);
 502                 goto cpu_master_loop;
 503         }
 504
 505         /*
 506          * CPU will loop if it is a slave or request to become a kgdb
 507          * master cpu and acquire the kgdb_active lock:
 508          */
 509         while (1) {
 510 cpu_loop:
 511                 if (kgdb_info[cpu].exception_state & DCPU_NEXT_MASTER) {
 512                         kgdb_info[cpu].exception_state &= ~DCPU_NEXT_MASTER;
 513                         goto cpu_master_loop;
 514                 } else if (kgdb_info[cpu].exception_state & DCPU_WANT_MASTER) {
 515                         if (raw_spin_trylock(&dbg_master_lock)) {
 516                                 atomic_xchg(&kgdb_active, cpu);
 517                                 break;
 518                         }
 519                 } else if (kgdb_info[cpu].exception_state & DCPU_IS_SLAVE) {
 520                         if (!raw_spin_is_locked(&dbg_slave_lock))
 521                                 goto return_normal;
 522                 } else {
 523 return_normal:
 524                         /* Return to normal operation by executing any
 525                          * hw breakpoint fixup.
 526                          */
 527                         if (arch_kgdb_ops.correct_hw_break)
 528                                 arch_kgdb_ops.correct_hw_break();
 529                         if (trace_on)
 530                                 tracing_on();
 531                         kgdb_info[cpu].exception_state &=
 532                                 ~(DCPU_WANT_MASTER | DCPU_IS_SLAVE);
 533                         kgdb_info[cpu].enter_kgdb--;
 534                         smp_mb__before_atomic();
 535                         atomic_dec(&slaves_in_kgdb);
 536                         dbg_touch_watchdogs();
 537                         local_irq_restore(flags);
 538                         rcu_read_unlock();
 539                         return 0;
 540                 }
 541                 cpu_relax();
 542         }
 543
 544         /*
 545          * For single stepping, try to only enter on the processor
 546          * that was single stepping.  To guard against a deadlock, the
 547          * kernel will only try for the value of sstep_tries before
 548          * giving up and continuing on.
 549          */
 550         if (atomic_read(&kgdb_cpu_doing_single_step) != -1 &&
 551             (kgdb_info[cpu].task &&
 552              kgdb_info[cpu].task->pid != kgdb_sstep_pid) && --sstep_tries) {
 553                 atomic_set(&kgdb_active, -1);
 554                 raw_spin_unlock(&dbg_master_lock);
 555                 dbg_touch_watchdogs();
 556                 local_irq_restore(flags);
 557                 rcu_read_unlock();
 558
 559                 goto acquirelock;
 560         }
 561
 562         if (!kgdb_io_ready(1)) {
 563                 kgdb_info[cpu].ret_state = 1;
 564                 goto kgdb_restore; /* No I/O connection, resume the system */
 565         }
 566
 567         /*
 568          * Don't enter if we have hit a removed breakpoint.
 569          */
 570         if (kgdb_skipexception(ks->ex_vector, ks->linux_regs))
 571                 goto kgdb_restore;
 572
 573         /* Call the I/O driver's pre_exception routine */
 574         if (dbg_io_ops->pre_exception)
 575                 dbg_io_ops->pre_exception();
 576
 577         /*
 578          * Get the passive CPU lock which will hold all the non-primary
 579          * CPU in a spin state while the debugger is active
 580          */
 581         if (!kgdb_single_step)
 582                 raw_spin_lock(&dbg_slave_lock);
 583
 584 #ifdef CONFIG_SMP
 585         /* If send_ready set, slaves are already waiting */
 586         if (ks->send_ready)
 587                 atomic_set(ks->send_ready, 1);
 588
 589         /* Signal the other CPUs to enter kgdb_wait() */
 590         else if ((!kgdb_single_step) && kgdb_do_roundup)
 591                 kgdb_roundup_cpus(flags);
 592 #endif
 593
 594         /*
 595          * Wait for the other CPUs to be notified and be waiting for us:
 596          */
 597         time_left = MSEC_PER_SEC;
 598         while (kgdb_do_roundup && --time_left &&
 599                (atomic_read(&masters_in_kgdb) + atomic_read(&slaves_in_kgdb)) !=
 600                    online_cpus)
 601                 udelay(1000);
 602         if (!time_left)
 603                 pr_crit("Timed out waiting for secondary CPUs.\n");
 604
 605         /*
 606          * At this point the primary processor is completely
 607          * in the debugger and all secondary CPUs are quiescent
 608          */
 609         dbg_deactivate_sw_breakpoints();
 610         kgdb_single_step = 0;
 611         kgdb_contthread = current;
 612         exception_level = 0;
 613         trace_on = tracing_is_on();
 614         if (trace_on)
 615                 tracing_off();
 616
 617         while (1) {
 618 cpu_master_loop:
 619                 if (dbg_kdb_mode) {
 620                         kgdb_connected = 1;
 621                         error = kdb_stub(ks);
 622                         if (error == -1)
 623                                 continue;
 624                         kgdb_connected = 0;
 625                 } else {
 626                         error = gdb_serial_stub(ks);
 627                 }
 628
 629                 if (error == DBG_PASS_EVENT) {
 630                         dbg_kdb_mode = !dbg_kdb_mode;
 631                 } else if (error == DBG_SWITCH_CPU_EVENT) {
 632                         kgdb_info[dbg_switch_cpu].exception_state |=
 633                                 DCPU_NEXT_MASTER;
 634                         goto cpu_loop;
 635                 } else {
 636                         kgdb_info[cpu].ret_state = error;
 637                         break;
 638                 }
 639         }
 640
 641         /* Call the I/O driver's post_exception routine */
 642         if (dbg_io_ops->post_exception)
 643                 dbg_io_ops->post_exception();
 644
 645         if (!kgdb_single_step) {
 646                 raw_spin_unlock(&dbg_slave_lock);
 647                 /* Wait till all the CPUs have quit from the debugger. */
 648                 while (kgdb_do_roundup && atomic_read(&slaves_in_kgdb))
 649                         cpu_relax();
 650         }
 651
 652 kgdb_restore:
 653         if (atomic_read(&kgdb_cpu_doing_single_step) != -1) {
 654                 int sstep_cpu = atomic_read(&kgdb_cpu_doing_single_step);
 655                 if (kgdb_info[sstep_cpu].task)
 656                         kgdb_sstep_pid = kgdb_info[sstep_cpu].task->pid;
 657                 else
 658                         kgdb_sstep_pid = 0;
 659         }
 660         if (arch_kgdb_ops.correct_hw_break)
 661                 arch_kgdb_ops.correct_hw_break();
 662         if (trace_on)
 663                 tracing_on();
 664
 665         kgdb_info[cpu].exception_state &=
 666                 ~(DCPU_WANT_MASTER | DCPU_IS_SLAVE);
 667         kgdb_info[cpu].enter_kgdb--;
 668         smp_mb__before_atomic();
 669         atomic_dec(&masters_in_kgdb);
 670         /* Free kgdb_active */
 671         atomic_set(&kgdb_active, -1);
 672         raw_spin_unlock(&dbg_master_lock);
 673         dbg_touch_watchdogs();
 674         local_irq_restore(flags);
 675         rcu_read_unlock();
 676
 677         return kgdb_info[cpu].ret_state;
 678 }
 679
 680 /*
 681  * kgdb_handle_exception() - main entry point from a kernel exception
 682  *
 683  * Locking hierarchy:
 684  *      interface locks, if any (begin_session)
 685  *      kgdb lock (kgdb_active)
 686  */
 687 int
 688 kgdb_handle_exception(int evector, int signo, int ecode, struct pt_regs *regs)
 689 {
 690         struct kgdb_state kgdb_var;
 691         struct kgdb_state *ks = &kgdb_var;
 692         int ret = 0;
 693
 694         if (arch_kgdb_ops.enable_nmi)
 695                 arch_kgdb_ops.enable_nmi(0);
 696         /*
 697          * Avoid entering the debugger if we were triggered due to an oops
 698          * but panic_timeout indicates the system should automatically
 699          * reboot on panic. We don't want to get stuck waiting for input
 700          * on such systems, especially if its "just" an oops.
 701          */
 702         if (signo != SIGTRAP && panic_timeout)
 703                 return 1;
 704
 705         memset(ks, 0, sizeof(struct kgdb_state));
 706         ks->cpu                 = raw_smp_processor_id();
 707         ks->ex_vector           = evector;
 708         ks->signo               = signo;
 709         ks->err_code            = ecode;
 710         ks->linux_regs          = regs;
 711
 712         if (kgdb_reenter_check(ks))
 713                 goto out; /* Ouch, double exception ! */
 714         if (kgdb_info[ks->cpu].enter_kgdb != 0)
 715                 goto out;
 716
 717         ret = kgdb_cpu_enter(ks, regs, DCPU_WANT_MASTER);
 718 out:
 719         if (arch_kgdb_ops.enable_nmi)
 720                 arch_kgdb_ops.enable_nmi(1);
 721         return ret;
 722 }
 723
 724 /*
 725  * GDB places a breakpoint at this function to know dynamically
 726  * loaded objects. It's not defined static so that only one instance with this
 727  * name exists in the kernel.
 728  */
 729
 730 static int module_event(struct notifier_block *self, unsigned long val,
 731         void *data)
 732 {
 733         return 0;
 734 }
 735
 736 static struct notifier_block dbg_module_load_nb = {
 737         .notifier_call  = module_event,
 738 };
 739
 740 int kgdb_nmicallback(int cpu, void *regs)
 741 {
 742 #ifdef CONFIG_SMP
 743         struct kgdb_state kgdb_var;
 744         struct kgdb_state *ks = &kgdb_var;
 745
 746         memset(ks, 0, sizeof(struct kgdb_state));
 747         ks->cpu                 = cpu;
 748         ks->linux_regs          = regs;
 749
 750         if (kgdb_info[ks->cpu].enter_kgdb == 0 &&
 751                         raw_spin_is_locked(&dbg_master_lock)) {
 752                 kgdb_cpu_enter(ks, regs, DCPU_IS_SLAVE);
 753                 return 0;
 754         }
 755 #endif
 756         return 1;
 757 }
 758
 759 int kgdb_nmicallin(int cpu, int trapnr, void *regs, int err_code,
 760                                                         atomic_t *send_ready)
 761 {
 762 #ifdef CONFIG_SMP
 763         if (!kgdb_io_ready(0) || !send_ready)
 764                 return 1;
 765
 766         if (kgdb_info[cpu].enter_kgdb == 0) {
 767                 struct kgdb_state kgdb_var;
 768                 struct kgdb_state *ks = &kgdb_var;
 769
 770                 memset(ks, 0, sizeof(struct kgdb_state));
 771                 ks->cpu                 = cpu;
 772                 ks->ex_vector           = trapnr;
 773                 ks->signo               = SIGTRAP;
 774                 ks->err_code            = err_code;
 775                 ks->linux_regs          = regs;
 776                 ks->send_ready          = send_ready;
 777                 kgdb_cpu_enter(ks, regs, DCPU_WANT_MASTER);
 778                 return 0;
 779         }
 780 #endif
 781         return 1;
 782 }
 783
 784 static void kgdb_console_write(struct console *co, const char *s,
 785    unsigned count)
 786 {
 787         unsigned long flags;
 788
 789         /* If we're debugging, or KGDB has not connected, don't try
 790          * and print. */
 791         if (!kgdb_connected || atomic_read(&kgdb_active) != -1 || dbg_kdb_mode)
 792                 return;
 793
 794         local_irq_save(flags);
 795         gdbstub_msg_write(s, count);
 796         local_irq_restore(flags);
 797 }
 798
 799 static struct console kgdbcons = {
 800         .name           = "kgdb",
 801         .write          = kgdb_console_write,
 802         .flags          = CON_PRINTBUFFER | CON_ENABLED,
 803         .index          = -1,
 804 };
 805
 806 static int __init opt_kgdb_con(char *str)
 807 {
 808         kgdb_use_con = 1;
 809
 810         if (kgdb_io_module_registered && !kgdb_con_registered) {
 811                 register_console(&kgdbcons);
 812                 kgdb_con_registered = 1;
 813         }
 814
 815         return 0;
 816 }
 817
 818 early_param("kgdbcon", opt_kgdb_con);
 819
 820 #ifdef CONFIG_MAGIC_SYSRQ
 821 static void sysrq_handle_dbg(int key)
 822 {
 823         if (!dbg_io_ops) {
 824                 pr_crit("ERROR: No KGDB I/O module available\n");
 825                 return;
 826         }
 827         if (!kgdb_connected) {
 828 #ifdef CONFIG_KGDB_KDB
 829                 if (!dbg_kdb_mode)
 830                         pr_crit("KGDB or $3#33 for KDB\n");
 831 #else
 832                 pr_crit("Entering KGDB\n");
 833 #endif
 834         }
 835
 836         kgdb_breakpoint();
 837 }
 838
 839 static struct sysrq_key_op sysrq_dbg_op = {
 840         .handler        = sysrq_handle_dbg,
 841         .help_msg       = "debug(g)",
 842         .action_msg     = "DEBUG",
 843 };
 844 #endif
 845
 846 static int kgdb_panic_event(struct notifier_block *self,
 847                             unsigned long val,
 848                             void *data)
 849 {
 850         /*
 851          * Avoid entering the debugger if we were triggered due to a panic
 852          * We don't want to get stuck waiting for input from user in such case.
 853          * panic_timeout indicates the system should automatically
 854          * reboot on panic.
 855          */
 856         if (panic_timeout)
 857                 return NOTIFY_DONE;
 858
 859         if (dbg_kdb_mode)
 860                 kdb_printf("PANIC: %s\n", (char *)data);
 861         kgdb_breakpoint();
 862         return NOTIFY_DONE;
 863 }
 864
 865 static struct notifier_block kgdb_panic_event_nb = {
 866        .notifier_call   = kgdb_panic_event,
 867        .priority        = INT_MAX,
 868 };
 869
 870 void __weak kgdb_arch_late(void)
 871 {
 872 }
 873
 874 void __init dbg_late_init(void)
 875 {
 876         dbg_is_early = false;
 877         if (kgdb_io_module_registered)
 878                 kgdb_arch_late();
 879         kdb_init(KDB_INIT_FULL);
 880 }
 881
 882 static int
 883 dbg_notify_reboot(struct notifier_block *this, unsigned long code, void *x)
 884 {
 885         /*
 886          * Take the following action on reboot notify depending on value:
 887          *    1 == Enter debugger
 888          *    0 == [the default] detatch debug client
 889          *   -1 == Do nothing... and use this until the board resets
 890          */
 891         switch (kgdbreboot) {
 892         case 1:
 893                 kgdb_breakpoint();
 894         case -1:
 895                 goto done;
 896         }
 897         if (!dbg_kdb_mode)
 898                 gdbstub_exit(code);
 899 done:
 900         return NOTIFY_DONE;
 901 }
 902
 903 static struct notifier_block dbg_reboot_notifier = {
 904         .notifier_call          = dbg_notify_reboot,
 905         .next                   = NULL,
 906         .priority               = INT_MAX,
 907 };
 908
 909 static void kgdb_register_callbacks(void)
 910 {
 911         if (!kgdb_io_module_registered) {
 912                 kgdb_io_module_registered = 1;
 913                 kgdb_arch_init();
 914                 if (!dbg_is_early)
 915                         kgdb_arch_late();
 916                 register_module_notifier(&dbg_module_load_nb);
 917                 register_reboot_notifier(&dbg_reboot_notifier);
 918                 atomic_notifier_chain_register(&panic_notifier_list,
 919                                                &kgdb_panic_event_nb);
 920 #ifdef CONFIG_MAGIC_SYSRQ
 921                 register_sysrq_key('g', &sysrq_dbg_op);
 922 #endif
 923                 if (kgdb_use_con && !kgdb_con_registered) {
 924                         register_console(&kgdbcons);
 925                         kgdb_con_registered = 1;
 926                 }
 927         }
 928 }
 929
 930 static void kgdb_unregister_callbacks(void)
 931 {
 932         /*
 933          * When this routine is called KGDB should unregister from the
 934          * panic handler and clean up, making sure it is not handling any
 935          * break exceptions at the time.
 936          */
 937         if (kgdb_io_module_registered) {
 938                 kgdb_io_module_registered = 0;
 939                 unregister_reboot_notifier(&dbg_reboot_notifier);
 940                 unregister_module_notifier(&dbg_module_load_nb);
 941                 atomic_notifier_chain_unregister(&panic_notifier_list,
 942                                                &kgdb_panic_event_nb);
 943                 kgdb_arch_exit();
 944 #ifdef CONFIG_MAGIC_SYSRQ
 945                 unregister_sysrq_key('g', &sysrq_dbg_op);
 946 #endif
 947                 if (kgdb_con_registered) {
 948                         unregister_console(&kgdbcons);
 949                         kgdb_con_registered = 0;
 950                 }
 951         }
 952 }
 953
 954 /*
 955  * There are times a tasklet needs to be used vs a compiled in
 956  * break point so as to cause an exception outside a kgdb I/O module,
 957  * such as is the case with kgdboe, where calling a breakpoint in the
 958  * I/O driver itself would be fatal.
 959  */
 960 static void kgdb_tasklet_bpt(unsigned long ing)
 961 {
 962         kgdb_breakpoint();
 963         atomic_set(&kgdb_break_tasklet_var, 0);
 964 }
 965
 966 static DECLARE_TASKLET(kgdb_tasklet_breakpoint, kgdb_tasklet_bpt, 0);
 967
 968 void kgdb_schedule_breakpoint(void)
 969 {
 970         if (atomic_read(&kgdb_break_tasklet_var) ||
 971                 atomic_read(&kgdb_active) != -1 ||
 972                 atomic_read(&kgdb_setting_breakpoint))
 973                 return;
 974         atomic_inc(&kgdb_break_tasklet_var);
 975         tasklet_schedule(&kgdb_tasklet_breakpoint);
 976 }
 977 EXPORT_SYMBOL_GPL(kgdb_schedule_breakpoint);
 978
 979 static void kgdb_initial_breakpoint(void)
 980 {
 981         kgdb_break_asap = 0;
 982
 983         pr_crit("Waiting for connection from remote gdb...\n");
 984         kgdb_breakpoint();
 985 }
 986
 987 /**
 988  *      kgdb_register_io_module - register KGDB IO module
 989  *      @new_dbg_io_ops: the io ops vector
 990  *
 991  *      Register it with the KGDB core.
 992  */
 993 int kgdb_register_io_module(struct kgdb_io *new_dbg_io_ops)
 994 {
 995         int err;
 996
 997         spin_lock(&kgdb_registration_lock);
 998
 999         if (dbg_io_ops) {
1000                 spin_unlock(&kgdb_registration_lock);
1001
1002                 pr_err("Another I/O driver is already registered with KGDB\n");
1003                 return -EBUSY;
1004         }
1005
1006         if (new_dbg_io_ops->init) {
1007                 err = new_dbg_io_ops->init();
1008                 if (err) {
1009                         spin_unlock(&kgdb_registration_lock);
1010                         return err;
1011                 }
1012         }
1013
1014         dbg_io_ops = new_dbg_io_ops;
1015
1016         spin_unlock(&kgdb_registration_lock);
1017
1018         pr_info("Registered I/O driver %s\n", new_dbg_io_ops->name);
1019
1020         /* Arm KGDB now. */
1021         kgdb_register_callbacks();
1022
1023         if (kgdb_break_asap)
1024                 kgdb_initial_breakpoint();
1025
1026         return 0;
1027 }
1028 EXPORT_SYMBOL_GPL(kgdb_register_io_module);
1029
1030 /**
1031  *      kkgdb_unregister_io_module - unregister KGDB IO module
1032  *      @old_dbg_io_ops: the io ops vector
1033  *
1034  *      Unregister it with the KGDB core.
1035  */
1036 void kgdb_unregister_io_module(struct kgdb_io *old_dbg_io_ops)
1037 {
1038         BUG_ON(kgdb_connected);
1039
1040         /*
1041          * KGDB is no longer able to communicate out, so
1042          * unregister our callbacks and reset state.
1043          */
1044         kgdb_unregister_callbacks();
1045
1046         spin_lock(&kgdb_registration_lock);
1047
1048         WARN_ON_ONCE(dbg_io_ops != old_dbg_io_ops);
1049         dbg_io_ops = NULL;
1050
1051         spin_unlock(&kgdb_registration_lock);
1052
1053         pr_info("Unregistered I/O driver %s, debugger disabled\n",
1054                 old_dbg_io_ops->name);
1055 }
1056 EXPORT_SYMBOL_GPL(kgdb_unregister_io_module);
1057
1058 int dbg_io_get_char(void)
1059 {
1060         int ret = dbg_io_ops->read_char();
1061         if (ret == NO_POLL_CHAR)
1062                 return -1;
1063         if (!dbg_kdb_mode)
1064                 return ret;
1065         if (ret == 127)
1066                 return 8;
1067         return ret;
1068 }
1069
1070 /**
1071  * kgdb_breakpoint - generate breakpoint exception
1072  *
1073  * This function will generate a breakpoint exception.  It is used at the
1074  * beginning of a program to sync up with a debugger and can be used
1075  * otherwise as a quick means to stop program execution and "break" into
1076  * the debugger.
1077  */
1078 noinline void kgdb_breakpoint(void)
1079 {
1080         atomic_inc(&kgdb_setting_breakpoint);
1081         wmb(); /* Sync point before breakpoint */
1082         arch_kgdb_breakpoint();
1083         wmb(); /* Sync point after breakpoint */
1084         atomic_dec(&kgdb_setting_breakpoint);
1085 }
1086 EXPORT_SYMBOL_GPL(kgdb_breakpoint);
1087
1088 static int __init opt_kgdb_wait(char *str)
1089 {
1090         kgdb_break_asap = 1;
1091
1092         kdb_init(KDB_INIT_EARLY);
1093         if (kgdb_io_module_registered)
1094                 kgdb_initial_breakpoint();
1095
1096         return 0;
1097 }
1098
1099 early_param("kgdbwait", opt_kgdb_wait);