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 #include <linux/irq.h>
  59
  60 #include <asm/cacheflush.h>
  61 #include <asm/byteorder.h>
  62 #include <linux/atomic.h>
  63
  64 #include "debug_core.h"
  65
  66 static int kgdb_break_asap;
  67
  68 struct debuggerinfo_struct kgdb_info[NR_CPUS];
  69
  70 /* kgdb_connected - Is a host GDB connected to us? */
  71 int                             kgdb_connected;
  72 EXPORT_SYMBOL_GPL(kgdb_connected);
  73
  74 /* All the KGDB handlers are installed */
  75 int                     kgdb_io_module_registered;
  76
  77 /* Guard for recursive entry */
  78 static int                      exception_level;
  79
  80 struct kgdb_io          *dbg_io_ops;
  81 static DEFINE_SPINLOCK(kgdb_registration_lock);
  82
  83 /* Action for the reboot notifiter, a global allow kdb to change it */
  84 static int kgdbreboot;
  85 /* kgdb console driver is loaded */
  86 static int kgdb_con_registered;
  87 /* determine if kgdb console output should be used */
  88 static int kgdb_use_con;
  89 /* Flag for alternate operations for early debugging */
  90 bool dbg_is_early = true;
  91 /* Next cpu to become the master debug core */
  92 int dbg_switch_cpu;
  93
  94 /* Use kdb or gdbserver mode */
  95 int dbg_kdb_mode = 1;
  96
  97 static int __init opt_kgdb_con(char *str)
  98 {
  99         kgdb_use_con = 1;
 100         return 0;
 101 }
 102
 103 early_param("kgdbcon", opt_kgdb_con);
 104
 105 module_param(kgdb_use_con, int, 0644);
 106 module_param(kgdbreboot, int, 0644);
 107
 108 /*
 109  * Holds information about breakpoints in a kernel. These breakpoints are
 110  * added and removed by gdb.
 111  */
 112 static struct kgdb_bkpt         kgdb_break[KGDB_MAX_BREAKPOINTS] = {
 113         [0 ... KGDB_MAX_BREAKPOINTS-1] = { .state = BP_UNDEFINED }
 114 };
 115
 116 /*
 117  * The CPU# of the active CPU, or -1 if none:
 118  */
 119 atomic_t                        kgdb_active = ATOMIC_INIT(-1);
 120 EXPORT_SYMBOL_GPL(kgdb_active);
 121 static DEFINE_RAW_SPINLOCK(dbg_master_lock);
 122 static DEFINE_RAW_SPINLOCK(dbg_slave_lock);
 123
 124 /*
 125  * We use NR_CPUs not PERCPU, in case kgdb is used to debug early
 126  * bootup code (which might not have percpu set up yet):
 127  */
 128 static atomic_t                 masters_in_kgdb;
 129 static atomic_t                 slaves_in_kgdb;
 130 static atomic_t                 kgdb_break_tasklet_var;
 131 atomic_t                        kgdb_setting_breakpoint;
 132
 133 struct task_struct              *kgdb_usethread;
 134 struct task_struct              *kgdb_contthread;
 135
 136 int                             kgdb_single_step;
 137 static pid_t                    kgdb_sstep_pid;
 138
 139 /* to keep track of the CPU which is doing the single stepping*/
 140 atomic_t                        kgdb_cpu_doing_single_step = ATOMIC_INIT(-1);
 141
 142 /*
 143  * If you are debugging a problem where roundup (the collection of
 144  * all other CPUs) is a problem [this should be extremely rare],
 145  * then use the nokgdbroundup option to avoid roundup. In that case
 146  * the other CPUs might interfere with your debugging context, so
 147  * use this with care:
 148  */
 149 static int kgdb_do_roundup = 1;
 150
 151 static int __init opt_nokgdbroundup(char *str)
 152 {
 153         kgdb_do_roundup = 0;
 154
 155         return 0;
 156 }
 157
 158 early_param("nokgdbroundup", opt_nokgdbroundup);
 159
 160 /*
 161  * Finally, some KGDB code :-)
 162  */
 163
 164 /*
 165  * Weak aliases for breakpoint management,
 166  * can be overriden by architectures when needed:
 167  */
 168 int __weak kgdb_arch_set_breakpoint(struct kgdb_bkpt *bpt)
 169 {
 170         int err;
 171
 172         err = copy_from_kernel_nofault(bpt->saved_instr, (char *)bpt->bpt_addr,
 173                                 BREAK_INSTR_SIZE);
 174         if (err)
 175                 return err;
 176         err = copy_to_kernel_nofault((char *)bpt->bpt_addr,
 177                                  arch_kgdb_ops.gdb_bpt_instr, BREAK_INSTR_SIZE);
 178         return err;
 179 }
 180
 181 int __weak kgdb_arch_remove_breakpoint(struct kgdb_bkpt *bpt)
 182 {
 183         return copy_to_kernel_nofault((char *)bpt->bpt_addr,
 184                                   (char *)bpt->saved_instr, BREAK_INSTR_SIZE);
 185 }
 186
 187 int __weak kgdb_validate_break_address(unsigned long addr)
 188 {
 189         struct kgdb_bkpt tmp;
 190         int err;
 191         /* Validate setting the breakpoint and then removing it.  If the
 192          * remove fails, the kernel needs to emit a bad message because we
 193          * are deep trouble not being able to put things back the way we
 194          * found them.
 195          */
 196         tmp.bpt_addr = addr;
 197         err = kgdb_arch_set_breakpoint(&tmp);
 198         if (err)
 199                 return err;
 200         err = kgdb_arch_remove_breakpoint(&tmp);
 201         if (err)
 202                 pr_err("Critical breakpoint error, kernel memory destroyed at: %lx\n",
 203                        addr);
 204         return err;
 205 }
 206
 207 unsigned long __weak kgdb_arch_pc(int exception, struct pt_regs *regs)
 208 {
 209         return instruction_pointer(regs);
 210 }
 211
 212 int __weak kgdb_arch_init(void)
 213 {
 214         return 0;
 215 }
 216
 217 int __weak kgdb_skipexception(int exception, struct pt_regs *regs)
 218 {
 219         return 0;
 220 }
 221
 222 #ifdef CONFIG_SMP
 223
 224 /*
 225  * Default (weak) implementation for kgdb_roundup_cpus
 226  */
 227
 228 static DEFINE_PER_CPU(call_single_data_t, kgdb_roundup_csd);
 229
 230 void __weak kgdb_call_nmi_hook(void *ignored)
 231 {
 232         /*
 233          * NOTE: get_irq_regs() is supposed to get the registers from
 234          * before the IPI interrupt happened and so is supposed to
 235          * show where the processor was.  In some situations it's
 236          * possible we might be called without an IPI, so it might be
 237          * safer to figure out how to make kgdb_breakpoint() work
 238          * properly here.
 239          */
 240         kgdb_nmicallback(raw_smp_processor_id(), get_irq_regs());
 241 }
 242
 243 void __weak kgdb_roundup_cpus(void)
 244 {
 245         call_single_data_t *csd;
 246         int this_cpu = raw_smp_processor_id();
 247         int cpu;
 248         int ret;
 249
 250         for_each_online_cpu(cpu) {
 251                 /* No need to roundup ourselves */
 252                 if (cpu == this_cpu)
 253                         continue;
 254
 255                 csd = &per_cpu(kgdb_roundup_csd, cpu);
 256
 257                 /*
 258                  * If it didn't round up last time, don't try again
 259                  * since smp_call_function_single_async() will block.
 260                  *
 261                  * If rounding_up is false then we know that the
 262                  * previous call must have at least started and that
 263                  * means smp_call_function_single_async() won't block.
 264                  */
 265                 if (kgdb_info[cpu].rounding_up)
 266                         continue;
 267                 kgdb_info[cpu].rounding_up = true;
 268
 269                 csd->func = kgdb_call_nmi_hook;
 270                 ret = smp_call_function_single_async(cpu, csd);
 271                 if (ret)
 272                         kgdb_info[cpu].rounding_up = false;
 273         }
 274 }
 275
 276 #endif
 277
 278 /*
 279  * Some architectures need cache flushes when we set/clear a
 280  * breakpoint:
 281  */
 282 static void kgdb_flush_swbreak_addr(unsigned long addr)
 283 {
 284         if (!CACHE_FLUSH_IS_SAFE)
 285                 return;
 286
 287         if (current->mm) {
 288                 int i;
 289
 290                 for (i = 0; i < VMACACHE_SIZE; i++) {
 291                         if (!current->vmacache.vmas[i])
 292                                 continue;
 293                         flush_cache_range(current->vmacache.vmas[i],
 294                                           addr, addr + BREAK_INSTR_SIZE);
 295                 }
 296         }
 297
 298         /* Force flush instruction cache if it was outside the mm */
 299         flush_icache_range(addr, addr + BREAK_INSTR_SIZE);
 300 }
 301
 302 /*
 303  * SW breakpoint management:
 304  */
 305 int dbg_activate_sw_breakpoints(void)
 306 {
 307         int error;
 308         int ret = 0;
 309         int i;
 310
 311         for (i = 0; i < KGDB_MAX_BREAKPOINTS; i++) {
 312                 if (kgdb_break[i].state != BP_SET)
 313                         continue;
 314
 315                 error = kgdb_arch_set_breakpoint(&kgdb_break[i]);
 316                 if (error) {
 317                         ret = error;
 318                         pr_info("BP install failed: %lx\n",
 319                                 kgdb_break[i].bpt_addr);
 320                         continue;
 321                 }
 322
 323                 kgdb_flush_swbreak_addr(kgdb_break[i].bpt_addr);
 324                 kgdb_break[i].state = BP_ACTIVE;
 325         }
 326         return ret;
 327 }
 328
 329 int dbg_set_sw_break(unsigned long addr)
 330 {
 331         int err = kgdb_validate_break_address(addr);
 332         int breakno = -1;
 333         int i;
 334
 335         if (err)
 336                 return err;
 337
 338         for (i = 0; i < KGDB_MAX_BREAKPOINTS; i++) {
 339                 if ((kgdb_break[i].state == BP_SET) &&
 340                                         (kgdb_break[i].bpt_addr == addr))
 341                         return -EEXIST;
 342         }
 343         for (i = 0; i < KGDB_MAX_BREAKPOINTS; i++) {
 344                 if (kgdb_break[i].state == BP_REMOVED &&
 345                                         kgdb_break[i].bpt_addr == addr) {
 346                         breakno = i;
 347                         break;
 348                 }
 349         }
 350
 351         if (breakno == -1) {
 352                 for (i = 0; i < KGDB_MAX_BREAKPOINTS; i++) {
 353                         if (kgdb_break[i].state == BP_UNDEFINED) {
 354                                 breakno = i;
 355                                 break;
 356                         }
 357                 }
 358         }
 359
 360         if (breakno == -1)
 361                 return -E2BIG;
 362
 363         kgdb_break[breakno].state = BP_SET;
 364         kgdb_break[breakno].type = BP_BREAKPOINT;
 365         kgdb_break[breakno].bpt_addr = addr;
 366
 367         return 0;
 368 }
 369
 370 int dbg_deactivate_sw_breakpoints(void)
 371 {
 372         int error;
 373         int ret = 0;
 374         int i;
 375
 376         for (i = 0; i < KGDB_MAX_BREAKPOINTS; i++) {
 377                 if (kgdb_break[i].state != BP_ACTIVE)
 378                         continue;
 379                 error = kgdb_arch_remove_breakpoint(&kgdb_break[i]);
 380                 if (error) {
 381                         pr_info("BP remove failed: %lx\n",
 382                                 kgdb_break[i].bpt_addr);
 383                         ret = error;
 384                 }
 385
 386                 kgdb_flush_swbreak_addr(kgdb_break[i].bpt_addr);
 387                 kgdb_break[i].state = BP_SET;
 388         }
 389         return ret;
 390 }
 391
 392 int dbg_remove_sw_break(unsigned long addr)
 393 {
 394         int i;
 395
 396         for (i = 0; i < KGDB_MAX_BREAKPOINTS; i++) {
 397                 if ((kgdb_break[i].state == BP_SET) &&
 398                                 (kgdb_break[i].bpt_addr == addr)) {
 399                         kgdb_break[i].state = BP_REMOVED;
 400                         return 0;
 401                 }
 402         }
 403         return -ENOENT;
 404 }
 405
 406 int kgdb_isremovedbreak(unsigned long addr)
 407 {
 408         int i;
 409
 410         for (i = 0; i < KGDB_MAX_BREAKPOINTS; i++) {
 411                 if ((kgdb_break[i].state == BP_REMOVED) &&
 412                                         (kgdb_break[i].bpt_addr == addr))
 413                         return 1;
 414         }
 415         return 0;
 416 }
 417
 418 int kgdb_has_hit_break(unsigned long addr)
 419 {
 420         int i;
 421
 422         for (i = 0; i < KGDB_MAX_BREAKPOINTS; i++) {
 423                 if (kgdb_break[i].state == BP_ACTIVE &&
 424                     kgdb_break[i].bpt_addr == addr)
 425                         return 1;
 426         }
 427         return 0;
 428 }
 429
 430 int dbg_remove_all_break(void)
 431 {
 432         int error;
 433         int i;
 434
 435         /* Clear memory breakpoints. */
 436         for (i = 0; i < KGDB_MAX_BREAKPOINTS; i++) {
 437                 if (kgdb_break[i].state != BP_ACTIVE)
 438                         goto setundefined;
 439                 error = kgdb_arch_remove_breakpoint(&kgdb_break[i]);
 440                 if (error)
 441                         pr_err("breakpoint remove failed: %lx\n",
 442                                kgdb_break[i].bpt_addr);
 443 setundefined:
 444                 kgdb_break[i].state = BP_UNDEFINED;
 445         }
 446
 447         /* Clear hardware breakpoints. */
 448         if (arch_kgdb_ops.remove_all_hw_break)
 449                 arch_kgdb_ops.remove_all_hw_break();
 450
 451         return 0;
 452 }
 453
 454 #ifdef CONFIG_KGDB_KDB
 455 void kdb_dump_stack_on_cpu(int cpu)
 456 {
 457         if (cpu == raw_smp_processor_id() || !IS_ENABLED(CONFIG_SMP)) {
 458                 dump_stack();
 459                 return;
 460         }
 461
 462         if (!(kgdb_info[cpu].exception_state & DCPU_IS_SLAVE)) {
 463                 kdb_printf("ERROR: Task on cpu %d didn't stop in the debugger\n",
 464                            cpu);
 465                 return;
 466         }
 467
 468         /*
 469          * In general, architectures don't support dumping the stack of a
 470          * "running" process that's not the current one.  From the point of
 471          * view of the Linux, kernel processes that are looping in the kgdb
 472          * slave loop are still "running".  There's also no API (that actually
 473          * works across all architectures) that can do a stack crawl based
 474          * on registers passed as a parameter.
 475          *
 476          * Solve this conundrum by asking slave CPUs to do the backtrace
 477          * themselves.
 478          */
 479         kgdb_info[cpu].exception_state |= DCPU_WANT_BT;
 480         while (kgdb_info[cpu].exception_state & DCPU_WANT_BT)
 481                 cpu_relax();
 482 }
 483 #endif
 484
 485 /*
 486  * Return true if there is a valid kgdb I/O module.  Also if no
 487  * debugger is attached a message can be printed to the console about
 488  * waiting for the debugger to attach.
 489  *
 490  * The print_wait argument is only to be true when called from inside
 491  * the core kgdb_handle_exception, because it will wait for the
 492  * debugger to attach.
 493  */
 494 static int kgdb_io_ready(int print_wait)
 495 {
 496         if (!dbg_io_ops)
 497                 return 0;
 498         if (kgdb_connected)
 499                 return 1;
 500         if (atomic_read(&kgdb_setting_breakpoint))
 501                 return 1;
 502         if (print_wait) {
 503 #ifdef CONFIG_KGDB_KDB
 504                 if (!dbg_kdb_mode)
 505                         pr_crit("waiting... or $3#33 for KDB\n");
 506 #else
 507                 pr_crit("Waiting for remote debugger\n");
 508 #endif
 509         }
 510         return 1;
 511 }
 512
 513 static int kgdb_reenter_check(struct kgdb_state *ks)
 514 {
 515         unsigned long addr;
 516
 517         if (atomic_read(&kgdb_active) != raw_smp_processor_id())
 518                 return 0;
 519
 520         /* Panic on recursive debugger calls: */
 521         exception_level++;
 522         addr = kgdb_arch_pc(ks->ex_vector, ks->linux_regs);
 523         dbg_deactivate_sw_breakpoints();
 524
 525         /*
 526          * If the break point removed ok at the place exception
 527          * occurred, try to recover and print a warning to the end
 528          * user because the user planted a breakpoint in a place that
 529          * KGDB needs in order to function.
 530          */
 531         if (dbg_remove_sw_break(addr) == 0) {
 532                 exception_level = 0;
 533                 kgdb_skipexception(ks->ex_vector, ks->linux_regs);
 534                 dbg_activate_sw_breakpoints();
 535                 pr_crit("re-enter error: breakpoint removed %lx\n", addr);
 536                 WARN_ON_ONCE(1);
 537
 538                 return 1;
 539         }
 540         dbg_remove_all_break();
 541         kgdb_skipexception(ks->ex_vector, ks->linux_regs);
 542
 543         if (exception_level > 1) {
 544                 dump_stack();
 545                 kgdb_io_module_registered = false;
 546                 panic("Recursive entry to debugger");
 547         }
 548
 549         pr_crit("re-enter exception: ALL breakpoints killed\n");
 550 #ifdef CONFIG_KGDB_KDB
 551         /* Allow kdb to debug itself one level */
 552         return 0;
 553 #endif
 554         dump_stack();
 555         panic("Recursive entry to debugger");
 556
 557         return 1;
 558 }
 559
 560 static void dbg_touch_watchdogs(void)
 561 {
 562         touch_softlockup_watchdog_sync();
 563         clocksource_touch_watchdog();
 564         rcu_cpu_stall_reset();
 565 }
 566
 567 static int kgdb_cpu_enter(struct kgdb_state *ks, struct pt_regs *regs,
 568                 int exception_state)
 569 {
 570         unsigned long flags;
 571         int sstep_tries = 100;
 572         int error;
 573         int cpu;
 574         int trace_on = 0;
 575         int online_cpus = num_online_cpus();
 576         u64 time_left;
 577
 578         kgdb_info[ks->cpu].enter_kgdb++;
 579         kgdb_info[ks->cpu].exception_state |= exception_state;
 580
 581         if (exception_state == DCPU_WANT_MASTER)
 582                 atomic_inc(&masters_in_kgdb);
 583         else
 584                 atomic_inc(&slaves_in_kgdb);
 585
 586         if (arch_kgdb_ops.disable_hw_break)
 587                 arch_kgdb_ops.disable_hw_break(regs);
 588
 589 acquirelock:
 590         /*
 591          * Interrupts will be restored by the 'trap return' code, except when
 592          * single stepping.
 593          */
 594         local_irq_save(flags);
 595
 596         cpu = ks->cpu;
 597         kgdb_info[cpu].debuggerinfo = regs;
 598         kgdb_info[cpu].task = current;
 599         kgdb_info[cpu].ret_state = 0;
 600         kgdb_info[cpu].irq_depth = hardirq_count() >> HARDIRQ_SHIFT;
 601
 602         /* Make sure the above info reaches the primary CPU */
 603         smp_mb();
 604
 605         if (exception_level == 1) {
 606                 if (raw_spin_trylock(&dbg_master_lock))
 607                         atomic_xchg(&kgdb_active, cpu);
 608                 goto cpu_master_loop;
 609         }
 610
 611         /*
 612          * CPU will loop if it is a slave or request to become a kgdb
 613          * master cpu and acquire the kgdb_active lock:
 614          */
 615         while (1) {
 616 cpu_loop:
 617                 if (kgdb_info[cpu].exception_state & DCPU_NEXT_MASTER) {
 618                         kgdb_info[cpu].exception_state &= ~DCPU_NEXT_MASTER;
 619                         goto cpu_master_loop;
 620                 } else if (kgdb_info[cpu].exception_state & DCPU_WANT_MASTER) {
 621                         if (raw_spin_trylock(&dbg_master_lock)) {
 622                                 atomic_xchg(&kgdb_active, cpu);
 623                                 break;
 624                         }
 625                 } else if (kgdb_info[cpu].exception_state & DCPU_WANT_BT) {
 626                         dump_stack();
 627                         kgdb_info[cpu].exception_state &= ~DCPU_WANT_BT;
 628                 } else if (kgdb_info[cpu].exception_state & DCPU_IS_SLAVE) {
 629                         if (!raw_spin_is_locked(&dbg_slave_lock))
 630                                 goto return_normal;
 631                 } else {
 632 return_normal:
 633                         /* Return to normal operation by executing any
 634                          * hw breakpoint fixup.
 635                          */
 636                         if (arch_kgdb_ops.correct_hw_break)
 637                                 arch_kgdb_ops.correct_hw_break();
 638                         if (trace_on)
 639                                 tracing_on();
 640                         kgdb_info[cpu].debuggerinfo = NULL;
 641                         kgdb_info[cpu].task = NULL;
 642                         kgdb_info[cpu].exception_state &=
 643                                 ~(DCPU_WANT_MASTER | DCPU_IS_SLAVE);
 644                         kgdb_info[cpu].enter_kgdb--;
 645                         smp_mb__before_atomic();
 646                         atomic_dec(&slaves_in_kgdb);
 647                         dbg_touch_watchdogs();
 648                         local_irq_restore(flags);
 649                         return 0;
 650                 }
 651                 cpu_relax();
 652         }
 653
 654         /*
 655          * For single stepping, try to only enter on the processor
 656          * that was single stepping.  To guard against a deadlock, the
 657          * kernel will only try for the value of sstep_tries before
 658          * giving up and continuing on.
 659          */
 660         if (atomic_read(&kgdb_cpu_doing_single_step) != -1 &&
 661             (kgdb_info[cpu].task &&
 662              kgdb_info[cpu].task->pid != kgdb_sstep_pid) && --sstep_tries) {
 663                 atomic_set(&kgdb_active, -1);
 664                 raw_spin_unlock(&dbg_master_lock);
 665                 dbg_touch_watchdogs();
 666                 local_irq_restore(flags);
 667
 668                 goto acquirelock;
 669         }
 670
 671         if (!kgdb_io_ready(1)) {
 672                 kgdb_info[cpu].ret_state = 1;
 673                 goto kgdb_restore; /* No I/O connection, resume the system */
 674         }
 675
 676         /*
 677          * Don't enter if we have hit a removed breakpoint.
 678          */
 679         if (kgdb_skipexception(ks->ex_vector, ks->linux_regs))
 680                 goto kgdb_restore;
 681
 682         atomic_inc(&ignore_console_lock_warning);
 683
 684         /* Call the I/O driver's pre_exception routine */
 685         if (dbg_io_ops->pre_exception)
 686                 dbg_io_ops->pre_exception();
 687
 688         /*
 689          * Get the passive CPU lock which will hold all the non-primary
 690          * CPU in a spin state while the debugger is active
 691          */
 692         if (!kgdb_single_step)
 693                 raw_spin_lock(&dbg_slave_lock);
 694
 695 #ifdef CONFIG_SMP
 696         /* If send_ready set, slaves are already waiting */
 697         if (ks->send_ready)
 698                 atomic_set(ks->send_ready, 1);
 699
 700         /* Signal the other CPUs to enter kgdb_wait() */
 701         else if ((!kgdb_single_step) && kgdb_do_roundup)
 702                 kgdb_roundup_cpus();
 703 #endif
 704
 705         /*
 706          * Wait for the other CPUs to be notified and be waiting for us:
 707          */
 708         time_left = MSEC_PER_SEC;
 709         while (kgdb_do_roundup && --time_left &&
 710                (atomic_read(&masters_in_kgdb) + atomic_read(&slaves_in_kgdb)) !=
 711                    online_cpus)
 712                 udelay(1000);
 713         if (!time_left)
 714                 pr_crit("Timed out waiting for secondary CPUs.\n");
 715
 716         /*
 717          * At this point the primary processor is completely
 718          * in the debugger and all secondary CPUs are quiescent
 719          */
 720         dbg_deactivate_sw_breakpoints();
 721         kgdb_single_step = 0;
 722         kgdb_contthread = current;
 723         exception_level = 0;
 724         trace_on = tracing_is_on();
 725         if (trace_on)
 726                 tracing_off();
 727
 728         while (1) {
 729 cpu_master_loop:
 730                 if (dbg_kdb_mode) {
 731                         kgdb_connected = 1;
 732                         error = kdb_stub(ks);
 733                         if (error == -1)
 734                                 continue;
 735                         kgdb_connected = 0;
 736                 } else {
 737                         error = gdb_serial_stub(ks);
 738                 }
 739
 740                 if (error == DBG_PASS_EVENT) {
 741                         dbg_kdb_mode = !dbg_kdb_mode;
 742                 } else if (error == DBG_SWITCH_CPU_EVENT) {
 743                         kgdb_info[dbg_switch_cpu].exception_state |=
 744                                 DCPU_NEXT_MASTER;
 745                         goto cpu_loop;
 746                 } else {
 747                         kgdb_info[cpu].ret_state = error;
 748                         break;
 749                 }
 750         }
 751
 752         /* Call the I/O driver's post_exception routine */
 753         if (dbg_io_ops->post_exception)
 754                 dbg_io_ops->post_exception();
 755
 756         atomic_dec(&ignore_console_lock_warning);
 757
 758         if (!kgdb_single_step) {
 759                 raw_spin_unlock(&dbg_slave_lock);
 760                 /* Wait till all the CPUs have quit from the debugger. */
 761                 while (kgdb_do_roundup && atomic_read(&slaves_in_kgdb))
 762                         cpu_relax();
 763         }
 764
 765 kgdb_restore:
 766         if (atomic_read(&kgdb_cpu_doing_single_step) != -1) {
 767                 int sstep_cpu = atomic_read(&kgdb_cpu_doing_single_step);
 768                 if (kgdb_info[sstep_cpu].task)
 769                         kgdb_sstep_pid = kgdb_info[sstep_cpu].task->pid;
 770                 else
 771                         kgdb_sstep_pid = 0;
 772         }
 773         if (arch_kgdb_ops.correct_hw_break)
 774                 arch_kgdb_ops.correct_hw_break();
 775         if (trace_on)
 776                 tracing_on();
 777
 778         kgdb_info[cpu].debuggerinfo = NULL;
 779         kgdb_info[cpu].task = NULL;
 780         kgdb_info[cpu].exception_state &=
 781                 ~(DCPU_WANT_MASTER | DCPU_IS_SLAVE);
 782         kgdb_info[cpu].enter_kgdb--;
 783         smp_mb__before_atomic();
 784         atomic_dec(&masters_in_kgdb);
 785         /* Free kgdb_active */
 786         atomic_set(&kgdb_active, -1);
 787         raw_spin_unlock(&dbg_master_lock);
 788         dbg_touch_watchdogs();
 789         local_irq_restore(flags);
 790
 791         return kgdb_info[cpu].ret_state;
 792 }
 793
 794 /*
 795  * kgdb_handle_exception() - main entry point from a kernel exception
 796  *
 797  * Locking hierarchy:
 798  *      interface locks, if any (begin_session)
 799  *      kgdb lock (kgdb_active)
 800  */
 801 int
 802 kgdb_handle_exception(int evector, int signo, int ecode, struct pt_regs *regs)
 803 {
 804         struct kgdb_state kgdb_var;
 805         struct kgdb_state *ks = &kgdb_var;
 806         int ret = 0;
 807
 808         if (arch_kgdb_ops.enable_nmi)
 809                 arch_kgdb_ops.enable_nmi(0);
 810         /*
 811          * Avoid entering the debugger if we were triggered due to an oops
 812          * but panic_timeout indicates the system should automatically
 813          * reboot on panic. We don't want to get stuck waiting for input
 814          * on such systems, especially if its "just" an oops.
 815          */
 816         if (signo != SIGTRAP && panic_timeout)
 817                 return 1;
 818
 819         memset(ks, 0, sizeof(struct kgdb_state));
 820         ks->cpu                 = raw_smp_processor_id();
 821         ks->ex_vector           = evector;
 822         ks->signo               = signo;
 823         ks->err_code            = ecode;
 824         ks->linux_regs          = regs;
 825
 826         if (kgdb_reenter_check(ks))
 827                 goto out; /* Ouch, double exception ! */
 828         if (kgdb_info[ks->cpu].enter_kgdb != 0)
 829                 goto out;
 830
 831         ret = kgdb_cpu_enter(ks, regs, DCPU_WANT_MASTER);
 832 out:
 833         if (arch_kgdb_ops.enable_nmi)
 834                 arch_kgdb_ops.enable_nmi(1);
 835         return ret;
 836 }
 837
 838 /*
 839  * GDB places a breakpoint at this function to know dynamically loaded objects.
 840  */
 841 static int module_event(struct notifier_block *self, unsigned long val,
 842         void *data)
 843 {
 844         return 0;
 845 }
 846
 847 static struct notifier_block dbg_module_load_nb = {
 848         .notifier_call  = module_event,
 849 };
 850
 851 int kgdb_nmicallback(int cpu, void *regs)
 852 {
 853 #ifdef CONFIG_SMP
 854         struct kgdb_state kgdb_var;
 855         struct kgdb_state *ks = &kgdb_var;
 856
 857         kgdb_info[cpu].rounding_up = false;
 858
 859         memset(ks, 0, sizeof(struct kgdb_state));
 860         ks->cpu                 = cpu;
 861         ks->linux_regs          = regs;
 862
 863         if (kgdb_info[ks->cpu].enter_kgdb == 0 &&
 864                         raw_spin_is_locked(&dbg_master_lock)) {
 865                 kgdb_cpu_enter(ks, regs, DCPU_IS_SLAVE);
 866                 return 0;
 867         }
 868 #endif
 869         return 1;
 870 }
 871
 872 int kgdb_nmicallin(int cpu, int trapnr, void *regs, int err_code,
 873                                                         atomic_t *send_ready)
 874 {
 875 #ifdef CONFIG_SMP
 876         if (!kgdb_io_ready(0) || !send_ready)
 877                 return 1;
 878
 879         if (kgdb_info[cpu].enter_kgdb == 0) {
 880                 struct kgdb_state kgdb_var;
 881                 struct kgdb_state *ks = &kgdb_var;
 882
 883                 memset(ks, 0, sizeof(struct kgdb_state));
 884                 ks->cpu                 = cpu;
 885                 ks->ex_vector           = trapnr;
 886                 ks->signo               = SIGTRAP;
 887                 ks->err_code            = err_code;
 888                 ks->linux_regs          = regs;
 889                 ks->send_ready          = send_ready;
 890                 kgdb_cpu_enter(ks, regs, DCPU_WANT_MASTER);
 891                 return 0;
 892         }
 893 #endif
 894         return 1;
 895 }
 896
 897 static void kgdb_console_write(struct console *co, const char *s,
 898    unsigned count)
 899 {
 900         unsigned long flags;
 901
 902         /* If we're debugging, or KGDB has not connected, don't try
 903          * and print. */
 904         if (!kgdb_connected || atomic_read(&kgdb_active) != -1 || dbg_kdb_mode)
 905                 return;
 906
 907         local_irq_save(flags);
 908         gdbstub_msg_write(s, count);
 909         local_irq_restore(flags);
 910 }
 911
 912 static struct console kgdbcons = {
 913         .name           = "kgdb",
 914         .write          = kgdb_console_write,
 915         .flags          = CON_PRINTBUFFER | CON_ENABLED,
 916         .index          = -1,
 917 };
 918
 919 #ifdef CONFIG_MAGIC_SYSRQ
 920 static void sysrq_handle_dbg(int key)
 921 {
 922         if (!dbg_io_ops) {
 923                 pr_crit("ERROR: No KGDB I/O module available\n");
 924                 return;
 925         }
 926         if (!kgdb_connected) {
 927 #ifdef CONFIG_KGDB_KDB
 928                 if (!dbg_kdb_mode)
 929                         pr_crit("KGDB or $3#33 for KDB\n");
 930 #else
 931                 pr_crit("Entering KGDB\n");
 932 #endif
 933         }
 934
 935         kgdb_breakpoint();
 936 }
 937
 938 static const struct sysrq_key_op sysrq_dbg_op = {
 939         .handler        = sysrq_handle_dbg,
 940         .help_msg       = "debug(g)",
 941         .action_msg     = "DEBUG",
 942 };
 943 #endif
 944
 945 void kgdb_panic(const char *msg)
 946 {
 947         if (!kgdb_io_module_registered)
 948                 return;
 949
 950         /*
 951          * We don't want to get stuck waiting for input from user if
 952          * "panic_timeout" indicates the system should automatically
 953          * reboot on panic.
 954          */
 955         if (panic_timeout)
 956                 return;
 957
 958         if (dbg_kdb_mode)
 959                 kdb_printf("PANIC: %s\n", msg);
 960
 961         kgdb_breakpoint();
 962 }
 963
 964 static void kgdb_initial_breakpoint(void)
 965 {
 966         kgdb_break_asap = 0;
 967
 968         pr_crit("Waiting for connection from remote gdb...\n");
 969         kgdb_breakpoint();
 970 }
 971
 972 void __weak kgdb_arch_late(void)
 973 {
 974 }
 975
 976 void __init dbg_late_init(void)
 977 {
 978         dbg_is_early = false;
 979         if (kgdb_io_module_registered)
 980                 kgdb_arch_late();
 981         kdb_init(KDB_INIT_FULL);
 982
 983         if (kgdb_io_module_registered && kgdb_break_asap)
 984                 kgdb_initial_breakpoint();
 985 }
 986
 987 static int
 988 dbg_notify_reboot(struct notifier_block *this, unsigned long code, void *x)
 989 {
 990         /*
 991          * Take the following action on reboot notify depending on value:
 992          *    1 == Enter debugger
 993          *    0 == [the default] detatch debug client
 994          *   -1 == Do nothing... and use this until the board resets
 995          */
 996         switch (kgdbreboot) {
 997         case 1:
 998                 kgdb_breakpoint();
 999         case -1:
1000                 goto done;
1001         }
1002         if (!dbg_kdb_mode)
1003                 gdbstub_exit(code);
1004 done:
1005         return NOTIFY_DONE;
1006 }
1007
1008 static struct notifier_block dbg_reboot_notifier = {
1009         .notifier_call          = dbg_notify_reboot,
1010         .next                   = NULL,
1011         .priority               = INT_MAX,
1012 };
1013
1014 static void kgdb_register_callbacks(void)
1015 {
1016         if (!kgdb_io_module_registered) {
1017                 kgdb_io_module_registered = 1;
1018                 kgdb_arch_init();
1019                 if (!dbg_is_early)
1020                         kgdb_arch_late();
1021                 register_module_notifier(&dbg_module_load_nb);
1022                 register_reboot_notifier(&dbg_reboot_notifier);
1023 #ifdef CONFIG_MAGIC_SYSRQ
1024                 register_sysrq_key('g', &sysrq_dbg_op);
1025 #endif
1026                 if (kgdb_use_con && !kgdb_con_registered) {
1027                         register_console(&kgdbcons);
1028                         kgdb_con_registered = 1;
1029                 }
1030         }
1031 }
1032
1033 static void kgdb_unregister_callbacks(void)
1034 {
1035         /*
1036          * When this routine is called KGDB should unregister from
1037          * handlers and clean up, making sure it is not handling any
1038          * break exceptions at the time.
1039          */
1040         if (kgdb_io_module_registered) {
1041                 kgdb_io_module_registered = 0;
1042                 unregister_reboot_notifier(&dbg_reboot_notifier);
1043                 unregister_module_notifier(&dbg_module_load_nb);
1044                 kgdb_arch_exit();
1045 #ifdef CONFIG_MAGIC_SYSRQ
1046                 unregister_sysrq_key('g', &sysrq_dbg_op);
1047 #endif
1048                 if (kgdb_con_registered) {
1049                         unregister_console(&kgdbcons);
1050                         kgdb_con_registered = 0;
1051                 }
1052         }
1053 }
1054
1055 /*
1056  * There are times a tasklet needs to be used vs a compiled in
1057  * break point so as to cause an exception outside a kgdb I/O module,
1058  * such as is the case with kgdboe, where calling a breakpoint in the
1059  * I/O driver itself would be fatal.
1060  */
1061 static void kgdb_tasklet_bpt(unsigned long ing)
1062 {
1063         kgdb_breakpoint();
1064         atomic_set(&kgdb_break_tasklet_var, 0);
1065 }
1066
1067 static DECLARE_TASKLET(kgdb_tasklet_breakpoint, kgdb_tasklet_bpt, 0);
1068
1069 void kgdb_schedule_breakpoint(void)
1070 {
1071         if (atomic_read(&kgdb_break_tasklet_var) ||
1072                 atomic_read(&kgdb_active) != -1 ||
1073                 atomic_read(&kgdb_setting_breakpoint))
1074                 return;
1075         atomic_inc(&kgdb_break_tasklet_var);
1076         tasklet_schedule(&kgdb_tasklet_breakpoint);
1077 }
1078 EXPORT_SYMBOL_GPL(kgdb_schedule_breakpoint);
1079
1080 /**
1081  *      kgdb_register_io_module - register KGDB IO module
1082  *      @new_dbg_io_ops: the io ops vector
1083  *
1084  *      Register it with the KGDB core.
1085  */
1086 int kgdb_register_io_module(struct kgdb_io *new_dbg_io_ops)
1087 {
1088         struct kgdb_io *old_dbg_io_ops;
1089         int err;
1090
1091         spin_lock(&kgdb_registration_lock);
1092
1093         old_dbg_io_ops = dbg_io_ops;
1094         if (old_dbg_io_ops) {
1095                 if (!old_dbg_io_ops->deinit) {
1096                         spin_unlock(&kgdb_registration_lock);
1097
1098                         pr_err("KGDB I/O driver %s can't replace %s.\n",
1099                                 new_dbg_io_ops->name, old_dbg_io_ops->name);
1100                         return -EBUSY;
1101                 }
1102                 pr_info("Replacing I/O driver %s with %s\n",
1103                         old_dbg_io_ops->name, new_dbg_io_ops->name);
1104         }
1105
1106         if (new_dbg_io_ops->init) {
1107                 err = new_dbg_io_ops->init();
1108                 if (err) {
1109                         spin_unlock(&kgdb_registration_lock);
1110                         return err;
1111                 }
1112         }
1113
1114         dbg_io_ops = new_dbg_io_ops;
1115
1116         spin_unlock(&kgdb_registration_lock);
1117
1118         if (old_dbg_io_ops) {
1119                 old_dbg_io_ops->deinit();
1120                 return 0;
1121         }
1122
1123         pr_info("Registered I/O driver %s\n", new_dbg_io_ops->name);
1124
1125         /* Arm KGDB now. */
1126         kgdb_register_callbacks();
1127
1128         if (kgdb_break_asap &&
1129             (!dbg_is_early || IS_ENABLED(CONFIG_ARCH_HAS_EARLY_DEBUG)))
1130                 kgdb_initial_breakpoint();
1131
1132         return 0;
1133 }
1134 EXPORT_SYMBOL_GPL(kgdb_register_io_module);
1135
1136 /**
1137  *      kkgdb_unregister_io_module - unregister KGDB IO module
1138  *      @old_dbg_io_ops: the io ops vector
1139  *
1140  *      Unregister it with the KGDB core.
1141  */
1142 void kgdb_unregister_io_module(struct kgdb_io *old_dbg_io_ops)
1143 {
1144         BUG_ON(kgdb_connected);
1145
1146         /*
1147          * KGDB is no longer able to communicate out, so
1148          * unregister our callbacks and reset state.
1149          */
1150         kgdb_unregister_callbacks();
1151
1152         spin_lock(&kgdb_registration_lock);
1153
1154         WARN_ON_ONCE(dbg_io_ops != old_dbg_io_ops);
1155         dbg_io_ops = NULL;
1156
1157         spin_unlock(&kgdb_registration_lock);
1158
1159         if (old_dbg_io_ops->deinit)
1160                 old_dbg_io_ops->deinit();
1161
1162         pr_info("Unregistered I/O driver %s, debugger disabled\n",
1163                 old_dbg_io_ops->name);
1164 }
1165 EXPORT_SYMBOL_GPL(kgdb_unregister_io_module);
1166
1167 int dbg_io_get_char(void)
1168 {
1169         int ret = dbg_io_ops->read_char();
1170         if (ret == NO_POLL_CHAR)
1171                 return -1;
1172         if (!dbg_kdb_mode)
1173                 return ret;
1174         if (ret == 127)
1175                 return 8;
1176         return ret;
1177 }
1178
1179 /**
1180  * kgdb_breakpoint - generate breakpoint exception
1181  *
1182  * This function will generate a breakpoint exception.  It is used at the
1183  * beginning of a program to sync up with a debugger and can be used
1184  * otherwise as a quick means to stop program execution and "break" into
1185  * the debugger.
1186  */
1187 noinline void kgdb_breakpoint(void)
1188 {
1189         atomic_inc(&kgdb_setting_breakpoint);
1190         wmb(); /* Sync point before breakpoint */
1191         arch_kgdb_breakpoint();
1192         wmb(); /* Sync point after breakpoint */
1193         atomic_dec(&kgdb_setting_breakpoint);
1194 }
1195 EXPORT_SYMBOL_GPL(kgdb_breakpoint);
1196
1197 static int __init opt_kgdb_wait(char *str)
1198 {
1199         kgdb_break_asap = 1;
1200
1201         kdb_init(KDB_INIT_EARLY);
1202         if (kgdb_io_module_registered &&
1203             IS_ENABLED(CONFIG_ARCH_HAS_EARLY_DEBUG))
1204                 kgdb_initial_breakpoint();
1205
1206         return 0;
1207 }
1208
1209 early_param("kgdbwait", opt_kgdb_wait);