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 #include <linux/pid_namespace.h>
  31 #include <linux/clocksource.h>
  32 #include <linux/interrupt.h>
  33 #include <linux/spinlock.h>
  34 #include <linux/console.h>
  35 #include <linux/threads.h>
  36 #include <linux/uaccess.h>
  37 #include <linux/kernel.h>
  38 #include <linux/module.h>
  39 #include <linux/ptrace.h>
  40 #include <linux/string.h>
  41 #include <linux/delay.h>
  42 #include <linux/sched.h>
  43 #include <linux/sysrq.h>
  44 #include <linux/init.h>
  45 #include <linux/kgdb.h>
  46 #include <linux/kdb.h>
  47 #include <linux/pid.h>
  48 #include <linux/smp.h>
  49 #include <linux/mm.h>
  50 #include <linux/rcupdate.h>
  51
  52 #include <asm/cacheflush.h>
  53 #include <asm/byteorder.h>
  54 #include <asm/atomic.h>
  55 #include <asm/system.h>
  56
  57 #include "debug_core.h"
  58
  59 static int kgdb_break_asap;
  60
  61 struct debuggerinfo_struct kgdb_info[NR_CPUS];
  62
  63 /**
  64  * kgdb_connected - Is a host GDB connected to us?
  65  */
  66 int                             kgdb_connected;
  67 EXPORT_SYMBOL_GPL(kgdb_connected);
  68
  69 /* All the KGDB handlers are installed */
  70 int                     kgdb_io_module_registered;
  71
  72 /* Guard for recursive entry */
  73 static int                      exception_level;
  74
  75 struct kgdb_io          *dbg_io_ops;
  76 static DEFINE_SPINLOCK(kgdb_registration_lock);
  77
  78 /* kgdb console driver is loaded */
  79 static int kgdb_con_registered;
  80 /* determine if kgdb console output should be used */
  81 static int kgdb_use_con;
  82 /* Flag for alternate operations for early debugging */
  83 bool dbg_is_early = true;
  84 /* Next cpu to become the master debug core */
  85 int dbg_switch_cpu;
  86
  87 /* Use kdb or gdbserver mode */
  88 int dbg_kdb_mode = 1;
  89
  90 static int __init opt_kgdb_con(char *str)
  91 {
  92         kgdb_use_con = 1;
  93         return 0;
  94 }
  95
  96 early_param("kgdbcon", opt_kgdb_con);
  97
  98 module_param(kgdb_use_con, 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(unsigned long addr, char *saved_instr)
 161 {
 162         int err;
 163
 164         err = probe_kernel_read(saved_instr, (char *)addr, BREAK_INSTR_SIZE);
 165         if (err)
 166                 return err;
 167
 168         return probe_kernel_write((char *)addr, arch_kgdb_ops.gdb_bpt_instr,
 169                                   BREAK_INSTR_SIZE);
 170 }
 171
 172 int __weak kgdb_arch_remove_breakpoint(unsigned long addr, char *bundle)
 173 {
 174         return probe_kernel_write((char *)addr,
 175                                   (char *)bundle, BREAK_INSTR_SIZE);
 176 }
 177
 178 int __weak kgdb_validate_break_address(unsigned long addr)
 179 {
 180         char tmp_variable[BREAK_INSTR_SIZE];
 181         int err;
 182         /* Validate setting the breakpoint and then removing it.  In the
 183          * remove fails, the kernel needs to emit a bad message because we
 184          * are deep trouble not being able to put things back the way we
 185          * found them.
 186          */
 187         err = kgdb_arch_set_breakpoint(addr, tmp_variable);
 188         if (err)
 189                 return err;
 190         err = kgdb_arch_remove_breakpoint(addr, tmp_variable);
 191         if (err)
 192                 printk(KERN_ERR "KGDB: Critical breakpoint error, kernel "
 193                    "memory destroyed at: %lx", addr);
 194         return err;
 195 }
 196
 197 unsigned long __weak kgdb_arch_pc(int exception, struct pt_regs *regs)
 198 {
 199         return instruction_pointer(regs);
 200 }
 201
 202 int __weak kgdb_arch_init(void)
 203 {
 204         return 0;
 205 }
 206
 207 int __weak kgdb_skipexception(int exception, struct pt_regs *regs)
 208 {
 209         return 0;
 210 }
 211
 212 /**
 213  *      kgdb_disable_hw_debug - Disable hardware debugging while we in kgdb.
 214  *      @regs: Current &struct pt_regs.
 215  *
 216  *      This function will be called if the particular architecture must
 217  *      disable hardware debugging while it is processing gdb packets or
 218  *      handling exception.
 219  */
 220 void __weak kgdb_disable_hw_debug(struct pt_regs *regs)
 221 {
 222 }
 223
 224 /*
 225  * Some architectures need cache flushes when we set/clear a
 226  * breakpoint:
 227  */
 228 static void kgdb_flush_swbreak_addr(unsigned long addr)
 229 {
 230         if (!CACHE_FLUSH_IS_SAFE)
 231                 return;
 232
 233         if (current->mm && current->mm->mmap_cache) {
 234                 flush_cache_range(current->mm->mmap_cache,
 235                                   addr, addr + BREAK_INSTR_SIZE);
 236         }
 237         /* Force flush instruction cache if it was outside the mm */
 238         flush_icache_range(addr, addr + BREAK_INSTR_SIZE);
 239 }
 240
 241 /*
 242  * SW breakpoint management:
 243  */
 244 int dbg_activate_sw_breakpoints(void)
 245 {
 246         unsigned long addr;
 247         int error;
 248         int ret = 0;
 249         int i;
 250
 251         for (i = 0; i < KGDB_MAX_BREAKPOINTS; i++) {
 252                 if (kgdb_break[i].state != BP_SET)
 253                         continue;
 254
 255                 addr = kgdb_break[i].bpt_addr;
 256                 error = kgdb_arch_set_breakpoint(addr,
 257                                 kgdb_break[i].saved_instr);
 258                 if (error) {
 259                         ret = error;
 260                         printk(KERN_INFO "KGDB: BP install failed: %lx", addr);
 261                         continue;
 262                 }
 263
 264                 kgdb_flush_swbreak_addr(addr);
 265                 kgdb_break[i].state = BP_ACTIVE;
 266         }
 267         return ret;
 268 }
 269
 270 int dbg_set_sw_break(unsigned long addr)
 271 {
 272         int err = kgdb_validate_break_address(addr);
 273         int breakno = -1;
 274         int i;
 275
 276         if (err)
 277                 return err;
 278
 279         for (i = 0; i < KGDB_MAX_BREAKPOINTS; i++) {
 280                 if ((kgdb_break[i].state == BP_SET) &&
 281                                         (kgdb_break[i].bpt_addr == addr))
 282                         return -EEXIST;
 283         }
 284         for (i = 0; i < KGDB_MAX_BREAKPOINTS; i++) {
 285                 if (kgdb_break[i].state == BP_REMOVED &&
 286                                         kgdb_break[i].bpt_addr == addr) {
 287                         breakno = i;
 288                         break;
 289                 }
 290         }
 291
 292         if (breakno == -1) {
 293                 for (i = 0; i < KGDB_MAX_BREAKPOINTS; i++) {
 294                         if (kgdb_break[i].state == BP_UNDEFINED) {
 295                                 breakno = i;
 296                                 break;
 297                         }
 298                 }
 299         }
 300
 301         if (breakno == -1)
 302                 return -E2BIG;
 303
 304         kgdb_break[breakno].state = BP_SET;
 305         kgdb_break[breakno].type = BP_BREAKPOINT;
 306         kgdb_break[breakno].bpt_addr = addr;
 307
 308         return 0;
 309 }
 310
 311 int dbg_deactivate_sw_breakpoints(void)
 312 {
 313         unsigned long addr;
 314         int error;
 315         int ret = 0;
 316         int i;
 317
 318         for (i = 0; i < KGDB_MAX_BREAKPOINTS; i++) {
 319                 if (kgdb_break[i].state != BP_ACTIVE)
 320                         continue;
 321                 addr = kgdb_break[i].bpt_addr;
 322                 error = kgdb_arch_remove_breakpoint(addr,
 323                                         kgdb_break[i].saved_instr);
 324                 if (error) {
 325                         printk(KERN_INFO "KGDB: BP remove failed: %lx\n", addr);
 326                         ret = error;
 327                 }
 328
 329                 kgdb_flush_swbreak_addr(addr);
 330                 kgdb_break[i].state = BP_SET;
 331         }
 332         return ret;
 333 }
 334
 335 int dbg_remove_sw_break(unsigned long addr)
 336 {
 337         int i;
 338
 339         for (i = 0; i < KGDB_MAX_BREAKPOINTS; i++) {
 340                 if ((kgdb_break[i].state == BP_SET) &&
 341                                 (kgdb_break[i].bpt_addr == addr)) {
 342                         kgdb_break[i].state = BP_REMOVED;
 343                         return 0;
 344                 }
 345         }
 346         return -ENOENT;
 347 }
 348
 349 int kgdb_isremovedbreak(unsigned long addr)
 350 {
 351         int i;
 352
 353         for (i = 0; i < KGDB_MAX_BREAKPOINTS; i++) {
 354                 if ((kgdb_break[i].state == BP_REMOVED) &&
 355                                         (kgdb_break[i].bpt_addr == addr))
 356                         return 1;
 357         }
 358         return 0;
 359 }
 360
 361 int dbg_remove_all_break(void)
 362 {
 363         unsigned long addr;
 364         int error;
 365         int i;
 366
 367         /* Clear memory breakpoints. */
 368         for (i = 0; i < KGDB_MAX_BREAKPOINTS; i++) {
 369                 if (kgdb_break[i].state != BP_ACTIVE)
 370                         goto setundefined;
 371                 addr = kgdb_break[i].bpt_addr;
 372                 error = kgdb_arch_remove_breakpoint(addr,
 373                                 kgdb_break[i].saved_instr);
 374                 if (error)
 375                         printk(KERN_ERR "KGDB: breakpoint remove failed: %lx\n",
 376                            addr);
 377 setundefined:
 378                 kgdb_break[i].state = BP_UNDEFINED;
 379         }
 380
 381         /* Clear hardware breakpoints. */
 382         if (arch_kgdb_ops.remove_all_hw_break)
 383                 arch_kgdb_ops.remove_all_hw_break();
 384
 385         return 0;
 386 }
 387
 388 /*
 389  * Return true if there is a valid kgdb I/O module.  Also if no
 390  * debugger is attached a message can be printed to the console about
 391  * waiting for the debugger to attach.
 392  *
 393  * The print_wait argument is only to be true when called from inside
 394  * the core kgdb_handle_exception, because it will wait for the
 395  * debugger to attach.
 396  */
 397 static int kgdb_io_ready(int print_wait)
 398 {
 399         if (!dbg_io_ops)
 400                 return 0;
 401         if (kgdb_connected)
 402                 return 1;
 403         if (atomic_read(&kgdb_setting_breakpoint))
 404                 return 1;
 405         if (print_wait) {
 406 #ifdef CONFIG_KGDB_KDB
 407                 if (!dbg_kdb_mode)
 408                         printk(KERN_CRIT "KGDB: waiting... or $3#33 for KDB\n");
 409 #else
 410                 printk(KERN_CRIT "KGDB: Waiting for remote debugger\n");
 411 #endif
 412         }
 413         return 1;
 414 }
 415
 416 static int kgdb_reenter_check(struct kgdb_state *ks)
 417 {
 418         unsigned long addr;
 419
 420         if (atomic_read(&kgdb_active) != raw_smp_processor_id())
 421                 return 0;
 422
 423         /* Panic on recursive debugger calls: */
 424         exception_level++;
 425         addr = kgdb_arch_pc(ks->ex_vector, ks->linux_regs);
 426         dbg_deactivate_sw_breakpoints();
 427
 428         /*
 429          * If the break point removed ok at the place exception
 430          * occurred, try to recover and print a warning to the end
 431          * user because the user planted a breakpoint in a place that
 432          * KGDB needs in order to function.
 433          */
 434         if (dbg_remove_sw_break(addr) == 0) {
 435                 exception_level = 0;
 436                 kgdb_skipexception(ks->ex_vector, ks->linux_regs);
 437                 dbg_activate_sw_breakpoints();
 438                 printk(KERN_CRIT "KGDB: re-enter error: breakpoint removed %lx\n",
 439                         addr);
 440                 WARN_ON_ONCE(1);
 441
 442                 return 1;
 443         }
 444         dbg_remove_all_break();
 445         kgdb_skipexception(ks->ex_vector, ks->linux_regs);
 446
 447         if (exception_level > 1) {
 448                 dump_stack();
 449                 panic("Recursive entry to debugger");
 450         }
 451
 452         printk(KERN_CRIT "KGDB: re-enter exception: ALL breakpoints killed\n");
 453 #ifdef CONFIG_KGDB_KDB
 454         /* Allow kdb to debug itself one level */
 455         return 0;
 456 #endif
 457         dump_stack();
 458         panic("Recursive entry to debugger");
 459
 460         return 1;
 461 }
 462
 463 static void dbg_touch_watchdogs(void)
 464 {
 465         touch_softlockup_watchdog_sync();
 466         clocksource_touch_watchdog();
 467         rcu_cpu_stall_reset();
 468 }
 469
 470 static int kgdb_cpu_enter(struct kgdb_state *ks, struct pt_regs *regs,
 471                 int exception_state)
 472 {
 473         unsigned long flags;
 474         int sstep_tries = 100;
 475         int error;
 476         int cpu;
 477         int trace_on = 0;
 478         int online_cpus = num_online_cpus();
 479
 480         kgdb_info[ks->cpu].enter_kgdb++;
 481         kgdb_info[ks->cpu].exception_state |= exception_state;
 482
 483         if (exception_state == DCPU_WANT_MASTER)
 484                 atomic_inc(&masters_in_kgdb);
 485         else
 486                 atomic_inc(&slaves_in_kgdb);
 487         kgdb_disable_hw_debug(ks->linux_regs);
 488
 489 acquirelock:
 490         /*
 491          * Interrupts will be restored by the 'trap return' code, except when
 492          * single stepping.
 493          */
 494         local_irq_save(flags);
 495
 496         cpu = ks->cpu;
 497         kgdb_info[cpu].debuggerinfo = regs;
 498         kgdb_info[cpu].task = current;
 499         kgdb_info[cpu].ret_state = 0;
 500         kgdb_info[cpu].irq_depth = hardirq_count() >> HARDIRQ_SHIFT;
 501
 502         /* Make sure the above info reaches the primary CPU */
 503         smp_mb();
 504
 505         if (exception_level == 1) {
 506                 if (raw_spin_trylock(&dbg_master_lock))
 507                         atomic_xchg(&kgdb_active, cpu);
 508                 goto cpu_master_loop;
 509         }
 510
 511         /*
 512          * CPU will loop if it is a slave or request to become a kgdb
 513          * master cpu and acquire the kgdb_active lock:
 514          */
 515         while (1) {
 516 cpu_loop:
 517                 if (kgdb_info[cpu].exception_state & DCPU_NEXT_MASTER) {
 518                         kgdb_info[cpu].exception_state &= ~DCPU_NEXT_MASTER;
 519                         goto cpu_master_loop;
 520                 } else if (kgdb_info[cpu].exception_state & DCPU_WANT_MASTER) {
 521                         if (raw_spin_trylock(&dbg_master_lock)) {
 522                                 atomic_xchg(&kgdb_active, cpu);
 523                                 break;
 524                         }
 525                 } else if (kgdb_info[cpu].exception_state & DCPU_IS_SLAVE) {
 526                         if (!raw_spin_is_locked(&dbg_slave_lock))
 527                                 goto return_normal;
 528                 } else {
 529 return_normal:
 530                         /* Return to normal operation by executing any
 531                          * hw breakpoint fixup.
 532                          */
 533                         if (arch_kgdb_ops.correct_hw_break)
 534                                 arch_kgdb_ops.correct_hw_break();
 535                         if (trace_on)
 536                                 tracing_on();
 537                         kgdb_info[cpu].exception_state &=
 538                                 ~(DCPU_WANT_MASTER | DCPU_IS_SLAVE);
 539                         kgdb_info[cpu].enter_kgdb--;
 540                         smp_mb__before_atomic_dec();
 541                         atomic_dec(&slaves_in_kgdb);
 542                         dbg_touch_watchdogs();
 543                         local_irq_restore(flags);
 544                         return 0;
 545                 }
 546                 cpu_relax();
 547         }
 548
 549         /*
 550          * For single stepping, try to only enter on the processor
 551          * that was single stepping.  To gaurd against a deadlock, the
 552          * kernel will only try for the value of sstep_tries before
 553          * giving up and continuing on.
 554          */
 555         if (atomic_read(&kgdb_cpu_doing_single_step) != -1 &&
 556             (kgdb_info[cpu].task &&
 557              kgdb_info[cpu].task->pid != kgdb_sstep_pid) && --sstep_tries) {
 558                 atomic_set(&kgdb_active, -1);
 559                 raw_spin_unlock(&dbg_master_lock);
 560                 dbg_touch_watchdogs();
 561                 local_irq_restore(flags);
 562
 563                 goto acquirelock;
 564         }
 565
 566         if (!kgdb_io_ready(1)) {
 567                 kgdb_info[cpu].ret_state = 1;
 568                 goto kgdb_restore; /* No I/O connection, resume the system */
 569         }
 570
 571         /*
 572          * Don't enter if we have hit a removed breakpoint.
 573          */
 574         if (kgdb_skipexception(ks->ex_vector, ks->linux_regs))
 575                 goto kgdb_restore;
 576
 577         /* Call the I/O driver's pre_exception routine */
 578         if (dbg_io_ops->pre_exception)
 579                 dbg_io_ops->pre_exception();
 580
 581         /*
 582          * Get the passive CPU lock which will hold all the non-primary
 583          * CPU in a spin state while the debugger is active
 584          */
 585         if (!kgdb_single_step)
 586                 raw_spin_lock(&dbg_slave_lock);
 587
 588 #ifdef CONFIG_SMP
 589         /* Signal the other CPUs to enter kgdb_wait() */
 590         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         while (kgdb_do_roundup && (atomic_read(&masters_in_kgdb) +
 598                                 atomic_read(&slaves_in_kgdb)) != online_cpus)
 599                 cpu_relax();
 600
 601         /*
 602          * At this point the primary processor is completely
 603          * in the debugger and all secondary CPUs are quiescent
 604          */
 605         dbg_deactivate_sw_breakpoints();
 606         kgdb_single_step = 0;
 607         kgdb_contthread = current;
 608         exception_level = 0;
 609         trace_on = tracing_is_on();
 610         if (trace_on)
 611                 tracing_off();
 612
 613         while (1) {
 614 cpu_master_loop:
 615                 if (dbg_kdb_mode) {
 616                         kgdb_connected = 1;
 617                         error = kdb_stub(ks);
 618                         if (error == -1)
 619                                 continue;
 620                         kgdb_connected = 0;
 621                 } else {
 622                         error = gdb_serial_stub(ks);
 623                 }
 624
 625                 if (error == DBG_PASS_EVENT) {
 626                         dbg_kdb_mode = !dbg_kdb_mode;
 627                 } else if (error == DBG_SWITCH_CPU_EVENT) {
 628                         kgdb_info[dbg_switch_cpu].exception_state |=
 629                                 DCPU_NEXT_MASTER;
 630                         goto cpu_loop;
 631                 } else {
 632                         kgdb_info[cpu].ret_state = error;
 633                         break;
 634                 }
 635         }
 636
 637         /* Call the I/O driver's post_exception routine */
 638         if (dbg_io_ops->post_exception)
 639                 dbg_io_ops->post_exception();
 640
 641         if (!kgdb_single_step) {
 642                 raw_spin_unlock(&dbg_slave_lock);
 643                 /* Wait till all the CPUs have quit from the debugger. */
 644                 while (kgdb_do_roundup && atomic_read(&slaves_in_kgdb))
 645                         cpu_relax();
 646         }
 647
 648 kgdb_restore:
 649         if (atomic_read(&kgdb_cpu_doing_single_step) != -1) {
 650                 int sstep_cpu = atomic_read(&kgdb_cpu_doing_single_step);
 651                 if (kgdb_info[sstep_cpu].task)
 652                         kgdb_sstep_pid = kgdb_info[sstep_cpu].task->pid;
 653                 else
 654                         kgdb_sstep_pid = 0;
 655         }
 656         if (arch_kgdb_ops.correct_hw_break)
 657                 arch_kgdb_ops.correct_hw_break();
 658         if (trace_on)
 659                 tracing_on();
 660
 661         kgdb_info[cpu].exception_state &=
 662                 ~(DCPU_WANT_MASTER | DCPU_IS_SLAVE);
 663         kgdb_info[cpu].enter_kgdb--;
 664         smp_mb__before_atomic_dec();
 665         atomic_dec(&masters_in_kgdb);
 666         /* Free kgdb_active */
 667         atomic_set(&kgdb_active, -1);
 668         raw_spin_unlock(&dbg_master_lock);
 669         dbg_touch_watchdogs();
 670         local_irq_restore(flags);
 671
 672         return kgdb_info[cpu].ret_state;
 673 }
 674
 675 /*
 676  * kgdb_handle_exception() - main entry point from a kernel exception
 677  *
 678  * Locking hierarchy:
 679  *      interface locks, if any (begin_session)
 680  *      kgdb lock (kgdb_active)
 681  */
 682 int
 683 kgdb_handle_exception(int evector, int signo, int ecode, struct pt_regs *regs)
 684 {
 685         struct kgdb_state kgdb_var;
 686         struct kgdb_state *ks = &kgdb_var;
 687
 688         ks->cpu                 = raw_smp_processor_id();
 689         ks->ex_vector           = evector;
 690         ks->signo               = signo;
 691         ks->err_code            = ecode;
 692         ks->kgdb_usethreadid    = 0;
 693         ks->linux_regs          = regs;
 694
 695         if (kgdb_reenter_check(ks))
 696                 return 0; /* Ouch, double exception ! */
 697         if (kgdb_info[ks->cpu].enter_kgdb != 0)
 698                 return 0;
 699
 700         return kgdb_cpu_enter(ks, regs, DCPU_WANT_MASTER);
 701 }
 702
 703 int kgdb_nmicallback(int cpu, void *regs)
 704 {
 705 #ifdef CONFIG_SMP
 706         struct kgdb_state kgdb_var;
 707         struct kgdb_state *ks = &kgdb_var;
 708
 709         memset(ks, 0, sizeof(struct kgdb_state));
 710         ks->cpu                 = cpu;
 711         ks->linux_regs          = regs;
 712
 713         if (kgdb_info[ks->cpu].enter_kgdb == 0 &&
 714                         raw_spin_is_locked(&dbg_master_lock)) {
 715                 kgdb_cpu_enter(ks, regs, DCPU_IS_SLAVE);
 716                 return 0;
 717         }
 718 #endif
 719         return 1;
 720 }
 721
 722 static void kgdb_console_write(struct console *co, const char *s,
 723    unsigned count)
 724 {
 725         unsigned long flags;
 726
 727         /* If we're debugging, or KGDB has not connected, don't try
 728          * and print. */
 729         if (!kgdb_connected || atomic_read(&kgdb_active) != -1 || dbg_kdb_mode)
 730                 return;
 731
 732         local_irq_save(flags);
 733         gdbstub_msg_write(s, count);
 734         local_irq_restore(flags);
 735 }
 736
 737 static struct console kgdbcons = {
 738         .name           = "kgdb",
 739         .write          = kgdb_console_write,
 740         .flags          = CON_PRINTBUFFER | CON_ENABLED,
 741         .index          = -1,
 742 };
 743
 744 #ifdef CONFIG_MAGIC_SYSRQ
 745 static void sysrq_handle_dbg(int key)
 746 {
 747         if (!dbg_io_ops) {
 748                 printk(KERN_CRIT "ERROR: No KGDB I/O module available\n");
 749                 return;
 750         }
 751         if (!kgdb_connected) {
 752 #ifdef CONFIG_KGDB_KDB
 753                 if (!dbg_kdb_mode)
 754                         printk(KERN_CRIT "KGDB or $3#33 for KDB\n");
 755 #else
 756                 printk(KERN_CRIT "Entering KGDB\n");
 757 #endif
 758         }
 759
 760         kgdb_breakpoint();
 761 }
 762
 763 static struct sysrq_key_op sysrq_dbg_op = {
 764         .handler        = sysrq_handle_dbg,
 765         .help_msg       = "debug(G)",
 766         .action_msg     = "DEBUG",
 767 };
 768 #endif
 769
 770 static int kgdb_panic_event(struct notifier_block *self,
 771                             unsigned long val,
 772                             void *data)
 773 {
 774         if (dbg_kdb_mode)
 775                 kdb_printf("PANIC: %s\n", (char *)data);
 776         kgdb_breakpoint();
 777         return NOTIFY_DONE;
 778 }
 779
 780 static struct notifier_block kgdb_panic_event_nb = {
 781        .notifier_call   = kgdb_panic_event,
 782        .priority        = INT_MAX,
 783 };
 784
 785 void __weak kgdb_arch_late(void)
 786 {
 787 }
 788
 789 void __init dbg_late_init(void)
 790 {
 791         dbg_is_early = false;
 792         if (kgdb_io_module_registered)
 793                 kgdb_arch_late();
 794         kdb_init(KDB_INIT_FULL);
 795 }
 796
 797 static void kgdb_register_callbacks(void)
 798 {
 799         if (!kgdb_io_module_registered) {
 800                 kgdb_io_module_registered = 1;
 801                 kgdb_arch_init();
 802                 if (!dbg_is_early)
 803                         kgdb_arch_late();
 804                 atomic_notifier_chain_register(&panic_notifier_list,
 805                                                &kgdb_panic_event_nb);
 806 #ifdef CONFIG_MAGIC_SYSRQ
 807                 register_sysrq_key('g', &sysrq_dbg_op);
 808 #endif
 809                 if (kgdb_use_con && !kgdb_con_registered) {
 810                         register_console(&kgdbcons);
 811                         kgdb_con_registered = 1;
 812                 }
 813         }
 814 }
 815
 816 static void kgdb_unregister_callbacks(void)
 817 {
 818         /*
 819          * When this routine is called KGDB should unregister from the
 820          * panic handler and clean up, making sure it is not handling any
 821          * break exceptions at the time.
 822          */
 823         if (kgdb_io_module_registered) {
 824                 kgdb_io_module_registered = 0;
 825                 atomic_notifier_chain_unregister(&panic_notifier_list,
 826                                                &kgdb_panic_event_nb);
 827                 kgdb_arch_exit();
 828 #ifdef CONFIG_MAGIC_SYSRQ
 829                 unregister_sysrq_key('g', &sysrq_dbg_op);
 830 #endif
 831                 if (kgdb_con_registered) {
 832                         unregister_console(&kgdbcons);
 833                         kgdb_con_registered = 0;
 834                 }
 835         }
 836 }
 837
 838 /*
 839  * There are times a tasklet needs to be used vs a compiled in
 840  * break point so as to cause an exception outside a kgdb I/O module,
 841  * such as is the case with kgdboe, where calling a breakpoint in the
 842  * I/O driver itself would be fatal.
 843  */
 844 static void kgdb_tasklet_bpt(unsigned long ing)
 845 {
 846         kgdb_breakpoint();
 847         atomic_set(&kgdb_break_tasklet_var, 0);
 848 }
 849
 850 static DECLARE_TASKLET(kgdb_tasklet_breakpoint, kgdb_tasklet_bpt, 0);
 851
 852 void kgdb_schedule_breakpoint(void)
 853 {
 854         if (atomic_read(&kgdb_break_tasklet_var) ||
 855                 atomic_read(&kgdb_active) != -1 ||
 856                 atomic_read(&kgdb_setting_breakpoint))
 857                 return;
 858         atomic_inc(&kgdb_break_tasklet_var);
 859         tasklet_schedule(&kgdb_tasklet_breakpoint);
 860 }
 861 EXPORT_SYMBOL_GPL(kgdb_schedule_breakpoint);
 862
 863 static void kgdb_initial_breakpoint(void)
 864 {
 865         kgdb_break_asap = 0;
 866
 867         printk(KERN_CRIT "kgdb: Waiting for connection from remote gdb...\n");
 868         kgdb_breakpoint();
 869 }
 870
 871 /**
 872  *      kgdb_register_io_module - register KGDB IO module
 873  *      @new_dbg_io_ops: the io ops vector
 874  *
 875  *      Register it with the KGDB core.
 876  */
 877 int kgdb_register_io_module(struct kgdb_io *new_dbg_io_ops)
 878 {
 879         int err;
 880
 881         spin_lock(&kgdb_registration_lock);
 882
 883         if (dbg_io_ops) {
 884                 spin_unlock(&kgdb_registration_lock);
 885
 886                 printk(KERN_ERR "kgdb: Another I/O driver is already "
 887                                 "registered with KGDB.\n");
 888                 return -EBUSY;
 889         }
 890
 891         if (new_dbg_io_ops->init) {
 892                 err = new_dbg_io_ops->init();
 893                 if (err) {
 894                         spin_unlock(&kgdb_registration_lock);
 895                         return err;
 896                 }
 897         }
 898
 899         dbg_io_ops = new_dbg_io_ops;
 900
 901         spin_unlock(&kgdb_registration_lock);
 902
 903         printk(KERN_INFO "kgdb: Registered I/O driver %s.\n",
 904                new_dbg_io_ops->name);
 905
 906         /* Arm KGDB now. */
 907         kgdb_register_callbacks();
 908
 909         if (kgdb_break_asap)
 910                 kgdb_initial_breakpoint();
 911
 912         return 0;
 913 }
 914 EXPORT_SYMBOL_GPL(kgdb_register_io_module);
 915
 916 /**
 917  *      kkgdb_unregister_io_module - unregister KGDB IO module
 918  *      @old_dbg_io_ops: the io ops vector
 919  *
 920  *      Unregister it with the KGDB core.
 921  */
 922 void kgdb_unregister_io_module(struct kgdb_io *old_dbg_io_ops)
 923 {
 924         BUG_ON(kgdb_connected);
 925
 926         /*
 927          * KGDB is no longer able to communicate out, so
 928          * unregister our callbacks and reset state.
 929          */
 930         kgdb_unregister_callbacks();
 931
 932         spin_lock(&kgdb_registration_lock);
 933
 934         WARN_ON_ONCE(dbg_io_ops != old_dbg_io_ops);
 935         dbg_io_ops = NULL;
 936
 937         spin_unlock(&kgdb_registration_lock);
 938
 939         printk(KERN_INFO
 940                 "kgdb: Unregistered I/O driver %s, debugger disabled.\n",
 941                 old_dbg_io_ops->name);
 942 }
 943 EXPORT_SYMBOL_GPL(kgdb_unregister_io_module);
 944
 945 int dbg_io_get_char(void)
 946 {
 947         int ret = dbg_io_ops->read_char();
 948         if (ret == NO_POLL_CHAR)
 949                 return -1;
 950         if (!dbg_kdb_mode)
 951                 return ret;
 952         if (ret == 127)
 953                 return 8;
 954         return ret;
 955 }
 956
 957 /**
 958  * kgdb_breakpoint - generate breakpoint exception
 959  *
 960  * This function will generate a breakpoint exception.  It is used at the
 961  * beginning of a program to sync up with a debugger and can be used
 962  * otherwise as a quick means to stop program execution and "break" into
 963  * the debugger.
 964  */
 965 void kgdb_breakpoint(void)
 966 {
 967         atomic_inc(&kgdb_setting_breakpoint);
 968         wmb(); /* Sync point before breakpoint */
 969         arch_kgdb_breakpoint();
 970         wmb(); /* Sync point after breakpoint */
 971         atomic_dec(&kgdb_setting_breakpoint);
 972 }
 973 EXPORT_SYMBOL_GPL(kgdb_breakpoint);
 974
 975 static int __init opt_kgdb_wait(char *str)
 976 {
 977         kgdb_break_asap = 1;
 978
 979         kdb_init(KDB_INIT_EARLY);
 980         if (kgdb_io_module_registered)
 981                 kgdb_initial_breakpoint();
 982
 983         return 0;
 984 }
 985
 986 early_param("kgdbwait", opt_kgdb_wait);