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         atomic_inc(&ignore_console_lock_warning);
 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         atomic_dec(&ignore_console_lock_warning);
 651
 652         if (!kgdb_single_step) {
 653                 raw_spin_unlock(&dbg_slave_lock);
 654                 /* Wait till all the CPUs have quit from the debugger. */
 655                 while (kgdb_do_roundup && atomic_read(&slaves_in_kgdb))
 656                         cpu_relax();
 657         }
 658
 659 kgdb_restore:
 660         if (atomic_read(&kgdb_cpu_doing_single_step) != -1) {
 661                 int sstep_cpu = atomic_read(&kgdb_cpu_doing_single_step);
 662                 if (kgdb_info[sstep_cpu].task)
 663                         kgdb_sstep_pid = kgdb_info[sstep_cpu].task->pid;
 664                 else
 665                         kgdb_sstep_pid = 0;
 666         }
 667         if (arch_kgdb_ops.correct_hw_break)
 668                 arch_kgdb_ops.correct_hw_break();
 669         if (trace_on)
 670                 tracing_on();
 671
 672         kgdb_info[cpu].debuggerinfo = NULL;
 673         kgdb_info[cpu].task = NULL;
 674         kgdb_info[cpu].exception_state &=
 675                 ~(DCPU_WANT_MASTER | DCPU_IS_SLAVE);
 676         kgdb_info[cpu].enter_kgdb--;
 677         smp_mb__before_atomic();
 678         atomic_dec(&masters_in_kgdb);
 679         /* Free kgdb_active */
 680         atomic_set(&kgdb_active, -1);
 681         raw_spin_unlock(&dbg_master_lock);
 682         dbg_touch_watchdogs();
 683         local_irq_restore(flags);
 684         rcu_read_unlock();
 685
 686         return kgdb_info[cpu].ret_state;
 687 }
 688
 689 /*
 690  * kgdb_handle_exception() - main entry point from a kernel exception
 691  *
 692  * Locking hierarchy:
 693  *      interface locks, if any (begin_session)
 694  *      kgdb lock (kgdb_active)
 695  */
 696 int
 697 kgdb_handle_exception(int evector, int signo, int ecode, struct pt_regs *regs)
 698 {
 699         struct kgdb_state kgdb_var;
 700         struct kgdb_state *ks = &kgdb_var;
 701         int ret = 0;
 702
 703         if (arch_kgdb_ops.enable_nmi)
 704                 arch_kgdb_ops.enable_nmi(0);
 705         /*
 706          * Avoid entering the debugger if we were triggered due to an oops
 707          * but panic_timeout indicates the system should automatically
 708          * reboot on panic. We don't want to get stuck waiting for input
 709          * on such systems, especially if its "just" an oops.
 710          */
 711         if (signo != SIGTRAP && panic_timeout)
 712                 return 1;
 713
 714         memset(ks, 0, sizeof(struct kgdb_state));
 715         ks->cpu                 = raw_smp_processor_id();
 716         ks->ex_vector           = evector;
 717         ks->signo               = signo;
 718         ks->err_code            = ecode;
 719         ks->linux_regs          = regs;
 720
 721         if (kgdb_reenter_check(ks))
 722                 goto out; /* Ouch, double exception ! */
 723         if (kgdb_info[ks->cpu].enter_kgdb != 0)
 724                 goto out;
 725
 726         ret = kgdb_cpu_enter(ks, regs, DCPU_WANT_MASTER);
 727 out:
 728         if (arch_kgdb_ops.enable_nmi)
 729                 arch_kgdb_ops.enable_nmi(1);
 730         return ret;
 731 }
 732
 733 /*
 734  * GDB places a breakpoint at this function to know dynamically
 735  * loaded objects. It's not defined static so that only one instance with this
 736  * name exists in the kernel.
 737  */
 738
 739 static int module_event(struct notifier_block *self, unsigned long val,
 740         void *data)
 741 {
 742         return 0;
 743 }
 744
 745 static struct notifier_block dbg_module_load_nb = {
 746         .notifier_call  = module_event,
 747 };
 748
 749 int kgdb_nmicallback(int cpu, void *regs)
 750 {
 751 #ifdef CONFIG_SMP
 752         struct kgdb_state kgdb_var;
 753         struct kgdb_state *ks = &kgdb_var;
 754
 755         memset(ks, 0, sizeof(struct kgdb_state));
 756         ks->cpu                 = cpu;
 757         ks->linux_regs          = regs;
 758
 759         if (kgdb_info[ks->cpu].enter_kgdb == 0 &&
 760                         raw_spin_is_locked(&dbg_master_lock)) {
 761                 kgdb_cpu_enter(ks, regs, DCPU_IS_SLAVE);
 762                 return 0;
 763         }
 764 #endif
 765         return 1;
 766 }
 767
 768 int kgdb_nmicallin(int cpu, int trapnr, void *regs, int err_code,
 769                                                         atomic_t *send_ready)
 770 {
 771 #ifdef CONFIG_SMP
 772         if (!kgdb_io_ready(0) || !send_ready)
 773                 return 1;
 774
 775         if (kgdb_info[cpu].enter_kgdb == 0) {
 776                 struct kgdb_state kgdb_var;
 777                 struct kgdb_state *ks = &kgdb_var;
 778
 779                 memset(ks, 0, sizeof(struct kgdb_state));
 780                 ks->cpu                 = cpu;
 781                 ks->ex_vector           = trapnr;
 782                 ks->signo               = SIGTRAP;
 783                 ks->err_code            = err_code;
 784                 ks->linux_regs          = regs;
 785                 ks->send_ready          = send_ready;
 786                 kgdb_cpu_enter(ks, regs, DCPU_WANT_MASTER);
 787                 return 0;
 788         }
 789 #endif
 790         return 1;
 791 }
 792
 793 static void kgdb_console_write(struct console *co, const char *s,
 794    unsigned count)
 795 {
 796         unsigned long flags;
 797
 798         /* If we're debugging, or KGDB has not connected, don't try
 799          * and print. */
 800         if (!kgdb_connected || atomic_read(&kgdb_active) != -1 || dbg_kdb_mode)
 801                 return;
 802
 803         local_irq_save(flags);
 804         gdbstub_msg_write(s, count);
 805         local_irq_restore(flags);
 806 }
 807
 808 static struct console kgdbcons = {
 809         .name           = "kgdb",
 810         .write          = kgdb_console_write,
 811         .flags          = CON_PRINTBUFFER | CON_ENABLED,
 812         .index          = -1,
 813 };
 814
 815 static int __init opt_kgdb_con(char *str)
 816 {
 817         kgdb_use_con = 1;
 818
 819         if (kgdb_io_module_registered && !kgdb_con_registered) {
 820                 register_console(&kgdbcons);
 821                 kgdb_con_registered = 1;
 822         }
 823
 824         return 0;
 825 }
 826
 827 early_param("kgdbcon", opt_kgdb_con);
 828
 829 #ifdef CONFIG_MAGIC_SYSRQ
 830 static void sysrq_handle_dbg(int key)
 831 {
 832         if (!dbg_io_ops) {
 833                 pr_crit("ERROR: No KGDB I/O module available\n");
 834                 return;
 835         }
 836         if (!kgdb_connected) {
 837 #ifdef CONFIG_KGDB_KDB
 838                 if (!dbg_kdb_mode)
 839                         pr_crit("KGDB or $3#33 for KDB\n");
 840 #else
 841                 pr_crit("Entering KGDB\n");
 842 #endif
 843         }
 844
 845         kgdb_breakpoint();
 846 }
 847
 848 static struct sysrq_key_op sysrq_dbg_op = {
 849         .handler        = sysrq_handle_dbg,
 850         .help_msg       = "debug(g)",
 851         .action_msg     = "DEBUG",
 852 };
 853 #endif
 854
 855 static int kgdb_panic_event(struct notifier_block *self,
 856                             unsigned long val,
 857                             void *data)
 858 {
 859         /*
 860          * Avoid entering the debugger if we were triggered due to a panic
 861          * We don't want to get stuck waiting for input from user in such case.
 862          * panic_timeout indicates the system should automatically
 863          * reboot on panic.
 864          */
 865         if (panic_timeout)
 866                 return NOTIFY_DONE;
 867
 868         if (dbg_kdb_mode)
 869                 kdb_printf("PANIC: %s\n", (char *)data);
 870         kgdb_breakpoint();
 871         return NOTIFY_DONE;
 872 }
 873
 874 static struct notifier_block kgdb_panic_event_nb = {
 875        .notifier_call   = kgdb_panic_event,
 876        .priority        = INT_MAX,
 877 };
 878
 879 void __weak kgdb_arch_late(void)
 880 {
 881 }
 882
 883 void __init dbg_late_init(void)
 884 {
 885         dbg_is_early = false;
 886         if (kgdb_io_module_registered)
 887                 kgdb_arch_late();
 888         kdb_init(KDB_INIT_FULL);
 889 }
 890
 891 static int
 892 dbg_notify_reboot(struct notifier_block *this, unsigned long code, void *x)
 893 {
 894         /*
 895          * Take the following action on reboot notify depending on value:
 896          *    1 == Enter debugger
 897          *    0 == [the default] detatch debug client
 898          *   -1 == Do nothing... and use this until the board resets
 899          */
 900         switch (kgdbreboot) {
 901         case 1:
 902                 kgdb_breakpoint();
 903         case -1:
 904                 goto done;
 905         }
 906         if (!dbg_kdb_mode)
 907                 gdbstub_exit(code);
 908 done:
 909         return NOTIFY_DONE;
 910 }
 911
 912 static struct notifier_block dbg_reboot_notifier = {
 913         .notifier_call          = dbg_notify_reboot,
 914         .next                   = NULL,
 915         .priority               = INT_MAX,
 916 };
 917
 918 static void kgdb_register_callbacks(void)
 919 {
 920         if (!kgdb_io_module_registered) {
 921                 kgdb_io_module_registered = 1;
 922                 kgdb_arch_init();
 923                 if (!dbg_is_early)
 924                         kgdb_arch_late();
 925                 register_module_notifier(&dbg_module_load_nb);
 926                 register_reboot_notifier(&dbg_reboot_notifier);
 927                 atomic_notifier_chain_register(&panic_notifier_list,
 928                                                &kgdb_panic_event_nb);
 929 #ifdef CONFIG_MAGIC_SYSRQ
 930                 register_sysrq_key('g', &sysrq_dbg_op);
 931 #endif
 932                 if (kgdb_use_con && !kgdb_con_registered) {
 933                         register_console(&kgdbcons);
 934                         kgdb_con_registered = 1;
 935                 }
 936         }
 937 }
 938
 939 static void kgdb_unregister_callbacks(void)
 940 {
 941         /*
 942          * When this routine is called KGDB should unregister from the
 943          * panic handler and clean up, making sure it is not handling any
 944          * break exceptions at the time.
 945          */
 946         if (kgdb_io_module_registered) {
 947                 kgdb_io_module_registered = 0;
 948                 unregister_reboot_notifier(&dbg_reboot_notifier);
 949                 unregister_module_notifier(&dbg_module_load_nb);
 950                 atomic_notifier_chain_unregister(&panic_notifier_list,
 951                                                &kgdb_panic_event_nb);
 952                 kgdb_arch_exit();
 953 #ifdef CONFIG_MAGIC_SYSRQ
 954                 unregister_sysrq_key('g', &sysrq_dbg_op);
 955 #endif
 956                 if (kgdb_con_registered) {
 957                         unregister_console(&kgdbcons);
 958                         kgdb_con_registered = 0;
 959                 }
 960         }
 961 }
 962
 963 /*
 964  * There are times a tasklet needs to be used vs a compiled in
 965  * break point so as to cause an exception outside a kgdb I/O module,
 966  * such as is the case with kgdboe, where calling a breakpoint in the
 967  * I/O driver itself would be fatal.
 968  */
 969 static void kgdb_tasklet_bpt(unsigned long ing)
 970 {
 971         kgdb_breakpoint();
 972         atomic_set(&kgdb_break_tasklet_var, 0);
 973 }
 974
 975 static DECLARE_TASKLET(kgdb_tasklet_breakpoint, kgdb_tasklet_bpt, 0);
 976
 977 void kgdb_schedule_breakpoint(void)
 978 {
 979         if (atomic_read(&kgdb_break_tasklet_var) ||
 980                 atomic_read(&kgdb_active) != -1 ||
 981                 atomic_read(&kgdb_setting_breakpoint))
 982                 return;
 983         atomic_inc(&kgdb_break_tasklet_var);
 984         tasklet_schedule(&kgdb_tasklet_breakpoint);
 985 }
 986 EXPORT_SYMBOL_GPL(kgdb_schedule_breakpoint);
 987
 988 static void kgdb_initial_breakpoint(void)
 989 {
 990         kgdb_break_asap = 0;
 991
 992         pr_crit("Waiting for connection from remote gdb...\n");
 993         kgdb_breakpoint();
 994 }
 995
 996 /**
 997  *      kgdb_register_io_module - register KGDB IO module
 998  *      @new_dbg_io_ops: the io ops vector
 999  *
1000  *      Register it with the KGDB core.
1001  */
1002 int kgdb_register_io_module(struct kgdb_io *new_dbg_io_ops)
1003 {
1004         int err;
1005
1006         spin_lock(&kgdb_registration_lock);
1007
1008         if (dbg_io_ops) {
1009                 spin_unlock(&kgdb_registration_lock);
1010
1011                 pr_err("Another I/O driver is already registered with KGDB\n");
1012                 return -EBUSY;
1013         }
1014
1015         if (new_dbg_io_ops->init) {
1016                 err = new_dbg_io_ops->init();
1017                 if (err) {
1018                         spin_unlock(&kgdb_registration_lock);
1019                         return err;
1020                 }
1021         }
1022
1023         dbg_io_ops = new_dbg_io_ops;
1024
1025         spin_unlock(&kgdb_registration_lock);
1026
1027         pr_info("Registered I/O driver %s\n", new_dbg_io_ops->name);
1028
1029         /* Arm KGDB now. */
1030         kgdb_register_callbacks();
1031
1032         if (kgdb_break_asap)
1033                 kgdb_initial_breakpoint();
1034
1035         return 0;
1036 }
1037 EXPORT_SYMBOL_GPL(kgdb_register_io_module);
1038
1039 /**
1040  *      kkgdb_unregister_io_module - unregister KGDB IO module
1041  *      @old_dbg_io_ops: the io ops vector
1042  *
1043  *      Unregister it with the KGDB core.
1044  */
1045 void kgdb_unregister_io_module(struct kgdb_io *old_dbg_io_ops)
1046 {
1047         BUG_ON(kgdb_connected);
1048
1049         /*
1050          * KGDB is no longer able to communicate out, so
1051          * unregister our callbacks and reset state.
1052          */
1053         kgdb_unregister_callbacks();
1054
1055         spin_lock(&kgdb_registration_lock);
1056
1057         WARN_ON_ONCE(dbg_io_ops != old_dbg_io_ops);
1058         dbg_io_ops = NULL;
1059
1060         spin_unlock(&kgdb_registration_lock);
1061
1062         pr_info("Unregistered I/O driver %s, debugger disabled\n",
1063                 old_dbg_io_ops->name);
1064 }
1065 EXPORT_SYMBOL_GPL(kgdb_unregister_io_module);
1066
1067 int dbg_io_get_char(void)
1068 {
1069         int ret = dbg_io_ops->read_char();
1070         if (ret == NO_POLL_CHAR)
1071                 return -1;
1072         if (!dbg_kdb_mode)
1073                 return ret;
1074         if (ret == 127)
1075                 return 8;
1076         return ret;
1077 }
1078
1079 /**
1080  * kgdb_breakpoint - generate breakpoint exception
1081  *
1082  * This function will generate a breakpoint exception.  It is used at the
1083  * beginning of a program to sync up with a debugger and can be used
1084  * otherwise as a quick means to stop program execution and "break" into
1085  * the debugger.
1086  */
1087 noinline void kgdb_breakpoint(void)
1088 {
1089         atomic_inc(&kgdb_setting_breakpoint);
1090         wmb(); /* Sync point before breakpoint */
1091         arch_kgdb_breakpoint();
1092         wmb(); /* Sync point after breakpoint */
1093         atomic_dec(&kgdb_setting_breakpoint);
1094 }
1095 EXPORT_SYMBOL_GPL(kgdb_breakpoint);
1096
1097 static int __init opt_kgdb_wait(char *str)
1098 {
1099         kgdb_break_asap = 1;
1100
1101         kdb_init(KDB_INIT_EARLY);
1102         if (kgdb_io_module_registered)
1103                 kgdb_initial_breakpoint();
1104
1105         return 0;
1106 }
1107
1108 early_param("kgdbwait", opt_kgdb_wait);