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 module_param(kgdb_use_con, int, 0644);
  99 module_param(kgdbreboot, int, 0644);
 100
 101 /*
 102  * Holds information about breakpoints in a kernel. These breakpoints are
 103  * added and removed by gdb.
 104  */
 105 static struct kgdb_bkpt         kgdb_break[KGDB_MAX_BREAKPOINTS] = {
 106         [0 ... KGDB_MAX_BREAKPOINTS-1] = { .state = BP_UNDEFINED }
 107 };
 108
 109 /*
 110  * The CPU# of the active CPU, or -1 if none:
 111  */
 112 atomic_t                        kgdb_active = ATOMIC_INIT(-1);
 113 EXPORT_SYMBOL_GPL(kgdb_active);
 114 static DEFINE_RAW_SPINLOCK(dbg_master_lock);
 115 static DEFINE_RAW_SPINLOCK(dbg_slave_lock);
 116
 117 /*
 118  * We use NR_CPUs not PERCPU, in case kgdb is used to debug early
 119  * bootup code (which might not have percpu set up yet):
 120  */
 121 static atomic_t                 masters_in_kgdb;
 122 static atomic_t                 slaves_in_kgdb;
 123 static atomic_t                 kgdb_break_tasklet_var;
 124 atomic_t                        kgdb_setting_breakpoint;
 125
 126 struct task_struct              *kgdb_usethread;
 127 struct task_struct              *kgdb_contthread;
 128
 129 int                             kgdb_single_step;
 130 static pid_t                    kgdb_sstep_pid;
 131
 132 /* to keep track of the CPU which is doing the single stepping*/
 133 atomic_t                        kgdb_cpu_doing_single_step = ATOMIC_INIT(-1);
 134
 135 /*
 136  * If you are debugging a problem where roundup (the collection of
 137  * all other CPUs) is a problem [this should be extremely rare],
 138  * then use the nokgdbroundup option to avoid roundup. In that case
 139  * the other CPUs might interfere with your debugging context, so
 140  * use this with care:
 141  */
 142 static int kgdb_do_roundup = 1;
 143
 144 static int __init opt_nokgdbroundup(char *str)
 145 {
 146         kgdb_do_roundup = 0;
 147
 148         return 0;
 149 }
 150
 151 early_param("nokgdbroundup", opt_nokgdbroundup);
 152
 153 /*
 154  * Finally, some KGDB code :-)
 155  */
 156
 157 /*
 158  * Weak aliases for breakpoint management,
 159  * can be overriden by architectures when needed:
 160  */
 161 int __weak kgdb_arch_set_breakpoint(struct kgdb_bkpt *bpt)
 162 {
 163         int err;
 164
 165         err = probe_kernel_read(bpt->saved_instr, (char *)bpt->bpt_addr,
 166                                 BREAK_INSTR_SIZE);
 167         if (err)
 168                 return err;
 169         err = probe_kernel_write((char *)bpt->bpt_addr,
 170                                  arch_kgdb_ops.gdb_bpt_instr, BREAK_INSTR_SIZE);
 171         return err;
 172 }
 173
 174 int __weak kgdb_arch_remove_breakpoint(struct kgdb_bkpt *bpt)
 175 {
 176         return probe_kernel_write((char *)bpt->bpt_addr,
 177                                   (char *)bpt->saved_instr, BREAK_INSTR_SIZE);
 178 }
 179
 180 int __weak kgdb_validate_break_address(unsigned long addr)
 181 {
 182         struct kgdb_bkpt tmp;
 183         int err;
 184         /* Validate setting the breakpoint and then removing it.  If the
 185          * remove fails, the kernel needs to emit a bad message because we
 186          * are deep trouble not being able to put things back the way we
 187          * found them.
 188          */
 189         tmp.bpt_addr = addr;
 190         err = kgdb_arch_set_breakpoint(&tmp);
 191         if (err)
 192                 return err;
 193         err = kgdb_arch_remove_breakpoint(&tmp);
 194         if (err)
 195                 pr_err("Critical breakpoint error, kernel memory destroyed at: %lx\n",
 196                        addr);
 197         return err;
 198 }
 199
 200 unsigned long __weak kgdb_arch_pc(int exception, struct pt_regs *regs)
 201 {
 202         return instruction_pointer(regs);
 203 }
 204
 205 int __weak kgdb_arch_init(void)
 206 {
 207         return 0;
 208 }
 209
 210 int __weak kgdb_skipexception(int exception, struct pt_regs *regs)
 211 {
 212         return 0;
 213 }
 214
 215 /*
 216  * Some architectures need cache flushes when we set/clear a
 217  * breakpoint:
 218  */
 219 static void kgdb_flush_swbreak_addr(unsigned long addr)
 220 {
 221         if (!CACHE_FLUSH_IS_SAFE)
 222                 return;
 223
 224         if (current->mm) {
 225                 int i;
 226
 227                 for (i = 0; i < VMACACHE_SIZE; i++) {
 228                         if (!current->vmacache.vmas[i])
 229                                 continue;
 230                         flush_cache_range(current->vmacache.vmas[i],
 231                                           addr, addr + BREAK_INSTR_SIZE);
 232                 }
 233         }
 234
 235         /* Force flush instruction cache if it was outside the mm */
 236         flush_icache_range(addr, addr + BREAK_INSTR_SIZE);
 237 }
 238
 239 /*
 240  * SW breakpoint management:
 241  */
 242 int dbg_activate_sw_breakpoints(void)
 243 {
 244         int error;
 245         int ret = 0;
 246         int i;
 247
 248         for (i = 0; i < KGDB_MAX_BREAKPOINTS; i++) {
 249                 if (kgdb_break[i].state != BP_SET)
 250                         continue;
 251
 252                 error = kgdb_arch_set_breakpoint(&kgdb_break[i]);
 253                 if (error) {
 254                         ret = error;
 255                         pr_info("BP install failed: %lx\n",
 256                                 kgdb_break[i].bpt_addr);
 257                         continue;
 258                 }
 259
 260                 kgdb_flush_swbreak_addr(kgdb_break[i].bpt_addr);
 261                 kgdb_break[i].state = BP_ACTIVE;
 262         }
 263         return ret;
 264 }
 265
 266 int dbg_set_sw_break(unsigned long addr)
 267 {
 268         int err = kgdb_validate_break_address(addr);
 269         int breakno = -1;
 270         int i;
 271
 272         if (err)
 273                 return err;
 274
 275         for (i = 0; i < KGDB_MAX_BREAKPOINTS; i++) {
 276                 if ((kgdb_break[i].state == BP_SET) &&
 277                                         (kgdb_break[i].bpt_addr == addr))
 278                         return -EEXIST;
 279         }
 280         for (i = 0; i < KGDB_MAX_BREAKPOINTS; i++) {
 281                 if (kgdb_break[i].state == BP_REMOVED &&
 282                                         kgdb_break[i].bpt_addr == addr) {
 283                         breakno = i;
 284                         break;
 285                 }
 286         }
 287
 288         if (breakno == -1) {
 289                 for (i = 0; i < KGDB_MAX_BREAKPOINTS; i++) {
 290                         if (kgdb_break[i].state == BP_UNDEFINED) {
 291                                 breakno = i;
 292                                 break;
 293                         }
 294                 }
 295         }
 296
 297         if (breakno == -1)
 298                 return -E2BIG;
 299
 300         kgdb_break[breakno].state = BP_SET;
 301         kgdb_break[breakno].type = BP_BREAKPOINT;
 302         kgdb_break[breakno].bpt_addr = addr;
 303
 304         return 0;
 305 }
 306
 307 int dbg_deactivate_sw_breakpoints(void)
 308 {
 309         int error;
 310         int ret = 0;
 311         int i;
 312
 313         for (i = 0; i < KGDB_MAX_BREAKPOINTS; i++) {
 314                 if (kgdb_break[i].state != BP_ACTIVE)
 315                         continue;
 316                 error = kgdb_arch_remove_breakpoint(&kgdb_break[i]);
 317                 if (error) {
 318                         pr_info("BP remove failed: %lx\n",
 319                                 kgdb_break[i].bpt_addr);
 320                         ret = error;
 321                 }
 322
 323                 kgdb_flush_swbreak_addr(kgdb_break[i].bpt_addr);
 324                 kgdb_break[i].state = BP_SET;
 325         }
 326         return ret;
 327 }
 328
 329 int dbg_remove_sw_break(unsigned long addr)
 330 {
 331         int i;
 332
 333         for (i = 0; i < KGDB_MAX_BREAKPOINTS; i++) {
 334                 if ((kgdb_break[i].state == BP_SET) &&
 335                                 (kgdb_break[i].bpt_addr == addr)) {
 336                         kgdb_break[i].state = BP_REMOVED;
 337                         return 0;
 338                 }
 339         }
 340         return -ENOENT;
 341 }
 342
 343 int kgdb_isremovedbreak(unsigned long addr)
 344 {
 345         int i;
 346
 347         for (i = 0; i < KGDB_MAX_BREAKPOINTS; i++) {
 348                 if ((kgdb_break[i].state == BP_REMOVED) &&
 349                                         (kgdb_break[i].bpt_addr == addr))
 350                         return 1;
 351         }
 352         return 0;
 353 }
 354
 355 int dbg_remove_all_break(void)
 356 {
 357         int error;
 358         int i;
 359
 360         /* Clear memory breakpoints. */
 361         for (i = 0; i < KGDB_MAX_BREAKPOINTS; i++) {
 362                 if (kgdb_break[i].state != BP_ACTIVE)
 363                         goto setundefined;
 364                 error = kgdb_arch_remove_breakpoint(&kgdb_break[i]);
 365                 if (error)
 366                         pr_err("breakpoint remove failed: %lx\n",
 367                                kgdb_break[i].bpt_addr);
 368 setundefined:
 369                 kgdb_break[i].state = BP_UNDEFINED;
 370         }
 371
 372         /* Clear hardware breakpoints. */
 373         if (arch_kgdb_ops.remove_all_hw_break)
 374                 arch_kgdb_ops.remove_all_hw_break();
 375
 376         return 0;
 377 }
 378
 379 /*
 380  * Return true if there is a valid kgdb I/O module.  Also if no
 381  * debugger is attached a message can be printed to the console about
 382  * waiting for the debugger to attach.
 383  *
 384  * The print_wait argument is only to be true when called from inside
 385  * the core kgdb_handle_exception, because it will wait for the
 386  * debugger to attach.
 387  */
 388 static int kgdb_io_ready(int print_wait)
 389 {
 390         if (!dbg_io_ops)
 391                 return 0;
 392         if (kgdb_connected)
 393                 return 1;
 394         if (atomic_read(&kgdb_setting_breakpoint))
 395                 return 1;
 396         if (print_wait) {
 397 #ifdef CONFIG_KGDB_KDB
 398                 if (!dbg_kdb_mode)
 399                         pr_crit("waiting... or $3#33 for KDB\n");
 400 #else
 401                 pr_crit("Waiting for remote debugger\n");
 402 #endif
 403         }
 404         return 1;
 405 }
 406
 407 static int kgdb_reenter_check(struct kgdb_state *ks)
 408 {
 409         unsigned long addr;
 410
 411         if (atomic_read(&kgdb_active) != raw_smp_processor_id())
 412                 return 0;
 413
 414         /* Panic on recursive debugger calls: */
 415         exception_level++;
 416         addr = kgdb_arch_pc(ks->ex_vector, ks->linux_regs);
 417         dbg_deactivate_sw_breakpoints();
 418
 419         /*
 420          * If the break point removed ok at the place exception
 421          * occurred, try to recover and print a warning to the end
 422          * user because the user planted a breakpoint in a place that
 423          * KGDB needs in order to function.
 424          */
 425         if (dbg_remove_sw_break(addr) == 0) {
 426                 exception_level = 0;
 427                 kgdb_skipexception(ks->ex_vector, ks->linux_regs);
 428                 dbg_activate_sw_breakpoints();
 429                 pr_crit("re-enter error: breakpoint removed %lx\n", addr);
 430                 WARN_ON_ONCE(1);
 431
 432                 return 1;
 433         }
 434         dbg_remove_all_break();
 435         kgdb_skipexception(ks->ex_vector, ks->linux_regs);
 436
 437         if (exception_level > 1) {
 438                 dump_stack();
 439                 kgdb_io_module_registered = false;
 440                 panic("Recursive entry to debugger");
 441         }
 442
 443         pr_crit("re-enter exception: ALL breakpoints killed\n");
 444 #ifdef CONFIG_KGDB_KDB
 445         /* Allow kdb to debug itself one level */
 446         return 0;
 447 #endif
 448         dump_stack();
 449         panic("Recursive entry to debugger");
 450
 451         return 1;
 452 }
 453
 454 static void dbg_touch_watchdogs(void)
 455 {
 456         touch_softlockup_watchdog_sync();
 457         clocksource_touch_watchdog();
 458         rcu_cpu_stall_reset();
 459 }
 460
 461 static int kgdb_cpu_enter(struct kgdb_state *ks, struct pt_regs *regs,
 462                 int exception_state)
 463 {
 464         unsigned long flags;
 465         int sstep_tries = 100;
 466         int error;
 467         int cpu;
 468         int trace_on = 0;
 469         int online_cpus = num_online_cpus();
 470         u64 time_left;
 471
 472         kgdb_info[ks->cpu].enter_kgdb++;
 473         kgdb_info[ks->cpu].exception_state |= exception_state;
 474
 475         if (exception_state == DCPU_WANT_MASTER)
 476                 atomic_inc(&masters_in_kgdb);
 477         else
 478                 atomic_inc(&slaves_in_kgdb);
 479
 480         if (arch_kgdb_ops.disable_hw_break)
 481                 arch_kgdb_ops.disable_hw_break(regs);
 482
 483 acquirelock:
 484         rcu_read_lock();
 485         /*
 486          * Interrupts will be restored by the 'trap return' code, except when
 487          * single stepping.
 488          */
 489         local_irq_save(flags);
 490
 491         cpu = ks->cpu;
 492         kgdb_info[cpu].debuggerinfo = regs;
 493         kgdb_info[cpu].task = current;
 494         kgdb_info[cpu].ret_state = 0;
 495         kgdb_info[cpu].irq_depth = hardirq_count() >> HARDIRQ_SHIFT;
 496
 497         /* Make sure the above info reaches the primary CPU */
 498         smp_mb();
 499
 500         if (exception_level == 1) {
 501                 if (raw_spin_trylock(&dbg_master_lock))
 502                         atomic_xchg(&kgdb_active, cpu);
 503                 goto cpu_master_loop;
 504         }
 505
 506         /*
 507          * CPU will loop if it is a slave or request to become a kgdb
 508          * master cpu and acquire the kgdb_active lock:
 509          */
 510         while (1) {
 511 cpu_loop:
 512                 if (kgdb_info[cpu].exception_state & DCPU_NEXT_MASTER) {
 513                         kgdb_info[cpu].exception_state &= ~DCPU_NEXT_MASTER;
 514                         goto cpu_master_loop;
 515                 } else if (kgdb_info[cpu].exception_state & DCPU_WANT_MASTER) {
 516                         if (raw_spin_trylock(&dbg_master_lock)) {
 517                                 atomic_xchg(&kgdb_active, cpu);
 518                                 break;
 519                         }
 520                 } else if (kgdb_info[cpu].exception_state & DCPU_IS_SLAVE) {
 521                         if (!raw_spin_is_locked(&dbg_slave_lock))
 522                                 goto return_normal;
 523                 } else {
 524 return_normal:
 525                         /* Return to normal operation by executing any
 526                          * hw breakpoint fixup.
 527                          */
 528                         if (arch_kgdb_ops.correct_hw_break)
 529                                 arch_kgdb_ops.correct_hw_break();
 530                         if (trace_on)
 531                                 tracing_on();
 532                         kgdb_info[cpu].debuggerinfo = NULL;
 533                         kgdb_info[cpu].task = NULL;
 534                         kgdb_info[cpu].exception_state &=
 535                                 ~(DCPU_WANT_MASTER | DCPU_IS_SLAVE);
 536                         kgdb_info[cpu].enter_kgdb--;
 537                         smp_mb__before_atomic();
 538                         atomic_dec(&slaves_in_kgdb);
 539                         dbg_touch_watchdogs();
 540                         local_irq_restore(flags);
 541                         rcu_read_unlock();
 542                         return 0;
 543                 }
 544                 cpu_relax();
 545         }
 546
 547         /*
 548          * For single stepping, try to only enter on the processor
 549          * that was single stepping.  To guard against a deadlock, the
 550          * kernel will only try for the value of sstep_tries before
 551          * giving up and continuing on.
 552          */
 553         if (atomic_read(&kgdb_cpu_doing_single_step) != -1 &&
 554             (kgdb_info[cpu].task &&
 555              kgdb_info[cpu].task->pid != kgdb_sstep_pid) && --sstep_tries) {
 556                 atomic_set(&kgdb_active, -1);
 557                 raw_spin_unlock(&dbg_master_lock);
 558                 dbg_touch_watchdogs();
 559                 local_irq_restore(flags);
 560                 rcu_read_unlock();
 561
 562                 goto acquirelock;
 563         }
 564
 565         if (!kgdb_io_ready(1)) {
 566                 kgdb_info[cpu].ret_state = 1;
 567                 goto kgdb_restore; /* No I/O connection, resume the system */
 568         }
 569
 570         /*
 571          * Don't enter if we have hit a removed breakpoint.
 572          */
 573         if (kgdb_skipexception(ks->ex_vector, ks->linux_regs))
 574                 goto kgdb_restore;
 575
 576         /* Call the I/O driver's pre_exception routine */
 577         if (dbg_io_ops->pre_exception)
 578                 dbg_io_ops->pre_exception();
 579
 580         /*
 581          * Get the passive CPU lock which will hold all the non-primary
 582          * CPU in a spin state while the debugger is active
 583          */
 584         if (!kgdb_single_step)
 585                 raw_spin_lock(&dbg_slave_lock);
 586
 587 #ifdef CONFIG_SMP
 588         /* If send_ready set, slaves are already waiting */
 589         if (ks->send_ready)
 590                 atomic_set(ks->send_ready, 1);
 591
 592         /* Signal the other CPUs to enter kgdb_wait() */
 593         else if ((!kgdb_single_step) && kgdb_do_roundup)
 594                 kgdb_roundup_cpus(flags);
 595 #endif
 596
 597         /*
 598          * Wait for the other CPUs to be notified and be waiting for us:
 599          */
 600         time_left = MSEC_PER_SEC;
 601         while (kgdb_do_roundup && --time_left &&
 602                (atomic_read(&masters_in_kgdb) + atomic_read(&slaves_in_kgdb)) !=
 603                    online_cpus)
 604                 udelay(1000);
 605         if (!time_left)
 606                 pr_crit("Timed out waiting for secondary CPUs.\n");
 607
 608         /*
 609          * At this point the primary processor is completely
 610          * in the debugger and all secondary CPUs are quiescent
 611          */
 612         dbg_deactivate_sw_breakpoints();
 613         kgdb_single_step = 0;
 614         kgdb_contthread = current;
 615         exception_level = 0;
 616         trace_on = tracing_is_on();
 617         if (trace_on)
 618                 tracing_off();
 619
 620         while (1) {
 621 cpu_master_loop:
 622                 if (dbg_kdb_mode) {
 623                         kgdb_connected = 1;
 624                         error = kdb_stub(ks);
 625                         if (error == -1)
 626                                 continue;
 627                         kgdb_connected = 0;
 628                 } else {
 629                         error = gdb_serial_stub(ks);
 630                 }
 631
 632                 if (error == DBG_PASS_EVENT) {
 633                         dbg_kdb_mode = !dbg_kdb_mode;
 634                 } else if (error == DBG_SWITCH_CPU_EVENT) {
 635                         kgdb_info[dbg_switch_cpu].exception_state |=
 636                                 DCPU_NEXT_MASTER;
 637                         goto cpu_loop;
 638                 } else {
 639                         kgdb_info[cpu].ret_state = error;
 640                         break;
 641                 }
 642         }
 643
 644         /* Call the I/O driver's post_exception routine */
 645         if (dbg_io_ops->post_exception)
 646                 dbg_io_ops->post_exception();
 647
 648         if (!kgdb_single_step) {
 649                 raw_spin_unlock(&dbg_slave_lock);
 650                 /* Wait till all the CPUs have quit from the debugger. */
 651                 while (kgdb_do_roundup && atomic_read(&slaves_in_kgdb))
 652                         cpu_relax();
 653         }
 654
 655 kgdb_restore:
 656         if (atomic_read(&kgdb_cpu_doing_single_step) != -1) {
 657                 int sstep_cpu = atomic_read(&kgdb_cpu_doing_single_step);
 658                 if (kgdb_info[sstep_cpu].task)
 659                         kgdb_sstep_pid = kgdb_info[sstep_cpu].task->pid;
 660                 else
 661                         kgdb_sstep_pid = 0;
 662         }
 663         if (arch_kgdb_ops.correct_hw_break)
 664                 arch_kgdb_ops.correct_hw_break();
 665         if (trace_on)
 666                 tracing_on();
 667
 668         kgdb_info[cpu].debuggerinfo = NULL;
 669         kgdb_info[cpu].task = NULL;
 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         rcu_read_unlock();
 681
 682         return kgdb_info[cpu].ret_state;
 683 }
 684
 685 /*
 686  * kgdb_handle_exception() - main entry point from a kernel exception
 687  *
 688  * Locking hierarchy:
 689  *      interface locks, if any (begin_session)
 690  *      kgdb lock (kgdb_active)
 691  */
 692 int
 693 kgdb_handle_exception(int evector, int signo, int ecode, struct pt_regs *regs)
 694 {
 695         struct kgdb_state kgdb_var;
 696         struct kgdb_state *ks = &kgdb_var;
 697         int ret = 0;
 698
 699         if (arch_kgdb_ops.enable_nmi)
 700                 arch_kgdb_ops.enable_nmi(0);
 701         /*
 702          * Avoid entering the debugger if we were triggered due to an oops
 703          * but panic_timeout indicates the system should automatically
 704          * reboot on panic. We don't want to get stuck waiting for input
 705          * on such systems, especially if its "just" an oops.
 706          */
 707         if (signo != SIGTRAP && panic_timeout)
 708                 return 1;
 709
 710         memset(ks, 0, sizeof(struct kgdb_state));
 711         ks->cpu                 = raw_smp_processor_id();
 712         ks->ex_vector           = evector;
 713         ks->signo               = signo;
 714         ks->err_code            = ecode;
 715         ks->linux_regs          = regs;
 716
 717         if (kgdb_reenter_check(ks))
 718                 goto out; /* Ouch, double exception ! */
 719         if (kgdb_info[ks->cpu].enter_kgdb != 0)
 720                 goto out;
 721
 722         ret = kgdb_cpu_enter(ks, regs, DCPU_WANT_MASTER);
 723 out:
 724         if (arch_kgdb_ops.enable_nmi)
 725                 arch_kgdb_ops.enable_nmi(1);
 726         return ret;
 727 }
 728
 729 /*
 730  * GDB places a breakpoint at this function to know dynamically
 731  * loaded objects. It's not defined static so that only one instance with this
 732  * name exists in the kernel.
 733  */
 734
 735 static int module_event(struct notifier_block *self, unsigned long val,
 736         void *data)
 737 {
 738         return 0;
 739 }
 740
 741 static struct notifier_block dbg_module_load_nb = {
 742         .notifier_call  = module_event,
 743 };
 744
 745 int kgdb_nmicallback(int cpu, void *regs)
 746 {
 747 #ifdef CONFIG_SMP
 748         struct kgdb_state kgdb_var;
 749         struct kgdb_state *ks = &kgdb_var;
 750
 751         memset(ks, 0, sizeof(struct kgdb_state));
 752         ks->cpu                 = cpu;
 753         ks->linux_regs          = regs;
 754
 755         if (kgdb_info[ks->cpu].enter_kgdb == 0 &&
 756                         raw_spin_is_locked(&dbg_master_lock)) {
 757                 kgdb_cpu_enter(ks, regs, DCPU_IS_SLAVE);
 758                 return 0;
 759         }
 760 #endif
 761         return 1;
 762 }
 763
 764 int kgdb_nmicallin(int cpu, int trapnr, void *regs, int err_code,
 765                                                         atomic_t *send_ready)
 766 {
 767 #ifdef CONFIG_SMP
 768         if (!kgdb_io_ready(0) || !send_ready)
 769                 return 1;
 770
 771         if (kgdb_info[cpu].enter_kgdb == 0) {
 772                 struct kgdb_state kgdb_var;
 773                 struct kgdb_state *ks = &kgdb_var;
 774
 775                 memset(ks, 0, sizeof(struct kgdb_state));
 776                 ks->cpu                 = cpu;
 777                 ks->ex_vector           = trapnr;
 778                 ks->signo               = SIGTRAP;
 779                 ks->err_code            = err_code;
 780                 ks->linux_regs          = regs;
 781                 ks->send_ready          = send_ready;
 782                 kgdb_cpu_enter(ks, regs, DCPU_WANT_MASTER);
 783                 return 0;
 784         }
 785 #endif
 786         return 1;
 787 }
 788
 789 static void kgdb_console_write(struct console *co, const char *s,
 790    unsigned count)
 791 {
 792         unsigned long flags;
 793
 794         /* If we're debugging, or KGDB has not connected, don't try
 795          * and print. */
 796         if (!kgdb_connected || atomic_read(&kgdb_active) != -1 || dbg_kdb_mode)
 797                 return;
 798
 799         local_irq_save(flags);
 800         gdbstub_msg_write(s, count);
 801         local_irq_restore(flags);
 802 }
 803
 804 static struct console kgdbcons = {
 805         .name           = "kgdb",
 806         .write          = kgdb_console_write,
 807         .flags          = CON_PRINTBUFFER | CON_ENABLED,
 808         .index          = -1,
 809 };
 810
 811 static int __init opt_kgdb_con(char *str)
 812 {
 813         kgdb_use_con = 1;
 814
 815         if (kgdb_io_module_registered && !kgdb_con_registered) {
 816                 register_console(&kgdbcons);
 817                 kgdb_con_registered = 1;
 818         }
 819
 820         return 0;
 821 }
 822
 823 early_param("kgdbcon", opt_kgdb_con);
 824
 825 #ifdef CONFIG_MAGIC_SYSRQ
 826 static void sysrq_handle_dbg(int key)
 827 {
 828         if (!dbg_io_ops) {
 829                 pr_crit("ERROR: No KGDB I/O module available\n");
 830                 return;
 831         }
 832         if (!kgdb_connected) {
 833 #ifdef CONFIG_KGDB_KDB
 834                 if (!dbg_kdb_mode)
 835                         pr_crit("KGDB or $3#33 for KDB\n");
 836 #else
 837                 pr_crit("Entering KGDB\n");
 838 #endif
 839         }
 840
 841         kgdb_breakpoint();
 842 }
 843
 844 static struct sysrq_key_op sysrq_dbg_op = {
 845         .handler        = sysrq_handle_dbg,
 846         .help_msg       = "debug(g)",
 847         .action_msg     = "DEBUG",
 848 };
 849 #endif
 850
 851 static int kgdb_panic_event(struct notifier_block *self,
 852                             unsigned long val,
 853                             void *data)
 854 {
 855         /*
 856          * Avoid entering the debugger if we were triggered due to a panic
 857          * We don't want to get stuck waiting for input from user in such case.
 858          * panic_timeout indicates the system should automatically
 859          * reboot on panic.
 860          */
 861         if (panic_timeout)
 862                 return NOTIFY_DONE;
 863
 864         if (dbg_kdb_mode)
 865                 kdb_printf("PANIC: %s\n", (char *)data);
 866         kgdb_breakpoint();
 867         return NOTIFY_DONE;
 868 }
 869
 870 static struct notifier_block kgdb_panic_event_nb = {
 871        .notifier_call   = kgdb_panic_event,
 872        .priority        = INT_MAX,
 873 };
 874
 875 void __weak kgdb_arch_late(void)
 876 {
 877 }
 878
 879 void __init dbg_late_init(void)
 880 {
 881         dbg_is_early = false;
 882         if (kgdb_io_module_registered)
 883                 kgdb_arch_late();
 884         kdb_init(KDB_INIT_FULL);
 885 }
 886
 887 static int
 888 dbg_notify_reboot(struct notifier_block *this, unsigned long code, void *x)
 889 {
 890         /*
 891          * Take the following action on reboot notify depending on value:
 892          *    1 == Enter debugger
 893          *    0 == [the default] detatch debug client
 894          *   -1 == Do nothing... and use this until the board resets
 895          */
 896         switch (kgdbreboot) {
 897         case 1:
 898                 kgdb_breakpoint();
 899         case -1:
 900                 goto done;
 901         }
 902         if (!dbg_kdb_mode)
 903                 gdbstub_exit(code);
 904 done:
 905         return NOTIFY_DONE;
 906 }
 907
 908 static struct notifier_block dbg_reboot_notifier = {
 909         .notifier_call          = dbg_notify_reboot,
 910         .next                   = NULL,
 911         .priority               = INT_MAX,
 912 };
 913
 914 static void kgdb_register_callbacks(void)
 915 {
 916         if (!kgdb_io_module_registered) {
 917                 kgdb_io_module_registered = 1;
 918                 kgdb_arch_init();
 919                 if (!dbg_is_early)
 920                         kgdb_arch_late();
 921                 register_module_notifier(&dbg_module_load_nb);
 922                 register_reboot_notifier(&dbg_reboot_notifier);
 923                 atomic_notifier_chain_register(&panic_notifier_list,
 924                                                &kgdb_panic_event_nb);
 925 #ifdef CONFIG_MAGIC_SYSRQ
 926                 register_sysrq_key('g', &sysrq_dbg_op);
 927 #endif
 928                 if (kgdb_use_con && !kgdb_con_registered) {
 929                         register_console(&kgdbcons);
 930                         kgdb_con_registered = 1;
 931                 }
 932         }
 933 }
 934
 935 static void kgdb_unregister_callbacks(void)
 936 {
 937         /*
 938          * When this routine is called KGDB should unregister from the
 939          * panic handler and clean up, making sure it is not handling any
 940          * break exceptions at the time.
 941          */
 942         if (kgdb_io_module_registered) {
 943                 kgdb_io_module_registered = 0;
 944                 unregister_reboot_notifier(&dbg_reboot_notifier);
 945                 unregister_module_notifier(&dbg_module_load_nb);
 946                 atomic_notifier_chain_unregister(&panic_notifier_list,
 947                                                &kgdb_panic_event_nb);
 948                 kgdb_arch_exit();
 949 #ifdef CONFIG_MAGIC_SYSRQ
 950                 unregister_sysrq_key('g', &sysrq_dbg_op);
 951 #endif
 952                 if (kgdb_con_registered) {
 953                         unregister_console(&kgdbcons);
 954                         kgdb_con_registered = 0;
 955                 }
 956         }
 957 }
 958
 959 /*
 960  * There are times a tasklet needs to be used vs a compiled in
 961  * break point so as to cause an exception outside a kgdb I/O module,
 962  * such as is the case with kgdboe, where calling a breakpoint in the
 963  * I/O driver itself would be fatal.
 964  */
 965 static void kgdb_tasklet_bpt(unsigned long ing)
 966 {
 967         kgdb_breakpoint();
 968         atomic_set(&kgdb_break_tasklet_var, 0);
 969 }
 970
 971 static DECLARE_TASKLET(kgdb_tasklet_breakpoint, kgdb_tasklet_bpt, 0);
 972
 973 void kgdb_schedule_breakpoint(void)
 974 {
 975         if (atomic_read(&kgdb_break_tasklet_var) ||
 976                 atomic_read(&kgdb_active) != -1 ||
 977                 atomic_read(&kgdb_setting_breakpoint))
 978                 return;
 979         atomic_inc(&kgdb_break_tasklet_var);
 980         tasklet_schedule(&kgdb_tasklet_breakpoint);
 981 }
 982 EXPORT_SYMBOL_GPL(kgdb_schedule_breakpoint);
 983
 984 static void kgdb_initial_breakpoint(void)
 985 {
 986         kgdb_break_asap = 0;
 987
 988         pr_crit("Waiting for connection from remote gdb...\n");
 989         kgdb_breakpoint();
 990 }
 991
 992 /**
 993  *      kgdb_register_io_module - register KGDB IO module
 994  *      @new_dbg_io_ops: the io ops vector
 995  *
 996  *      Register it with the KGDB core.
 997  */
 998 int kgdb_register_io_module(struct kgdb_io *new_dbg_io_ops)
 999 {
1000         int err;
1001
1002         spin_lock(&kgdb_registration_lock);
1003
1004         if (dbg_io_ops) {
1005                 spin_unlock(&kgdb_registration_lock);
1006
1007                 pr_err("Another I/O driver is already registered with KGDB\n");
1008                 return -EBUSY;
1009         }
1010
1011         if (new_dbg_io_ops->init) {
1012                 err = new_dbg_io_ops->init();
1013                 if (err) {
1014                         spin_unlock(&kgdb_registration_lock);
1015                         return err;
1016                 }
1017         }
1018
1019         dbg_io_ops = new_dbg_io_ops;
1020
1021         spin_unlock(&kgdb_registration_lock);
1022
1023         pr_info("Registered I/O driver %s\n", new_dbg_io_ops->name);
1024
1025         /* Arm KGDB now. */
1026         kgdb_register_callbacks();
1027
1028         if (kgdb_break_asap)
1029                 kgdb_initial_breakpoint();
1030
1031         return 0;
1032 }
1033 EXPORT_SYMBOL_GPL(kgdb_register_io_module);
1034
1035 /**
1036  *      kkgdb_unregister_io_module - unregister KGDB IO module
1037  *      @old_dbg_io_ops: the io ops vector
1038  *
1039  *      Unregister it with the KGDB core.
1040  */
1041 void kgdb_unregister_io_module(struct kgdb_io *old_dbg_io_ops)
1042 {
1043         BUG_ON(kgdb_connected);
1044
1045         /*
1046          * KGDB is no longer able to communicate out, so
1047          * unregister our callbacks and reset state.
1048          */
1049         kgdb_unregister_callbacks();
1050
1051         spin_lock(&kgdb_registration_lock);
1052
1053         WARN_ON_ONCE(dbg_io_ops != old_dbg_io_ops);
1054         dbg_io_ops = NULL;
1055
1056         spin_unlock(&kgdb_registration_lock);
1057
1058         pr_info("Unregistered I/O driver %s, debugger disabled\n",
1059                 old_dbg_io_ops->name);
1060 }
1061 EXPORT_SYMBOL_GPL(kgdb_unregister_io_module);
1062
1063 int dbg_io_get_char(void)
1064 {
1065         int ret = dbg_io_ops->read_char();
1066         if (ret == NO_POLL_CHAR)
1067                 return -1;
1068         if (!dbg_kdb_mode)
1069                 return ret;
1070         if (ret == 127)
1071                 return 8;
1072         return ret;
1073 }
1074
1075 /**
1076  * kgdb_breakpoint - generate breakpoint exception
1077  *
1078  * This function will generate a breakpoint exception.  It is used at the
1079  * beginning of a program to sync up with a debugger and can be used
1080  * otherwise as a quick means to stop program execution and "break" into
1081  * the debugger.
1082  */
1083 noinline void kgdb_breakpoint(void)
1084 {
1085         atomic_inc(&kgdb_setting_breakpoint);
1086         wmb(); /* Sync point before breakpoint */
1087         arch_kgdb_breakpoint();
1088         wmb(); /* Sync point after breakpoint */
1089         atomic_dec(&kgdb_setting_breakpoint);
1090 }
1091 EXPORT_SYMBOL_GPL(kgdb_breakpoint);
1092
1093 static int __init opt_kgdb_wait(char *str)
1094 {
1095         kgdb_break_asap = 1;
1096
1097         kdb_init(KDB_INIT_EARLY);
1098         if (kgdb_io_module_registered)
1099                 kgdb_initial_breakpoint();
1100
1101         return 0;
1102 }
1103
1104 early_param("kgdbwait", opt_kgdb_wait);