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 notifier, a global allow kdb to change it */
  84 static int kgdbreboot;
  85 /* kgdb console driver is loaded */
  86 static int kgdb_con_registered;
  87 /* determine if kgdb console output should be used */
  88 static int kgdb_use_con;
  89 /* Flag for alternate operations for early debugging */
  90 bool dbg_is_early = true;
  91 /* Next cpu to become the master debug core */
  92 int dbg_switch_cpu;
  93
  94 /* Use kdb or gdbserver mode */
  95 int dbg_kdb_mode = 1;
  96
  97 module_param(kgdb_use_con, int, 0644);
  98 module_param(kgdbreboot, int, 0644);
  99
 100 /*
 101  * Holds information about breakpoints in a kernel. These breakpoints are
 102  * added and removed by gdb.
 103  */
 104 static struct kgdb_bkpt         kgdb_break[KGDB_MAX_BREAKPOINTS] = {
 105         [0 ... KGDB_MAX_BREAKPOINTS-1] = { .state = BP_UNDEFINED }
 106 };
 107
 108 /*
 109  * The CPU# of the active CPU, or -1 if none:
 110  */
 111 atomic_t                        kgdb_active = ATOMIC_INIT(-1);
 112 EXPORT_SYMBOL_GPL(kgdb_active);
 113 static DEFINE_RAW_SPINLOCK(dbg_master_lock);
 114 static DEFINE_RAW_SPINLOCK(dbg_slave_lock);
 115
 116 /*
 117  * We use NR_CPUs not PERCPU, in case kgdb is used to debug early
 118  * bootup code (which might not have percpu set up yet):
 119  */
 120 static atomic_t                 masters_in_kgdb;
 121 static atomic_t                 slaves_in_kgdb;
 122 atomic_t                        kgdb_setting_breakpoint;
 123
 124 struct task_struct              *kgdb_usethread;
 125 struct task_struct              *kgdb_contthread;
 126
 127 int                             kgdb_single_step;
 128 static pid_t                    kgdb_sstep_pid;
 129
 130 /* to keep track of the CPU which is doing the single stepping*/
 131 atomic_t                        kgdb_cpu_doing_single_step = ATOMIC_INIT(-1);
 132
 133 /*
 134  * If you are debugging a problem where roundup (the collection of
 135  * all other CPUs) is a problem [this should be extremely rare],
 136  * then use the nokgdbroundup option to avoid roundup. In that case
 137  * the other CPUs might interfere with your debugging context, so
 138  * use this with care:
 139  */
 140 static int kgdb_do_roundup = 1;
 141
 142 static int __init opt_nokgdbroundup(char *str)
 143 {
 144         kgdb_do_roundup = 0;
 145
 146         return 0;
 147 }
 148
 149 early_param("nokgdbroundup", opt_nokgdbroundup);
 150
 151 /*
 152  * Finally, some KGDB code :-)
 153  */
 154
 155 /*
 156  * Weak aliases for breakpoint management,
 157  * can be overridden by architectures when needed:
 158  */
 159 int __weak kgdb_arch_set_breakpoint(struct kgdb_bkpt *bpt)
 160 {
 161         int err;
 162
 163         err = copy_from_kernel_nofault(bpt->saved_instr, (char *)bpt->bpt_addr,
 164                                 BREAK_INSTR_SIZE);
 165         if (err)
 166                 return err;
 167         err = copy_to_kernel_nofault((char *)bpt->bpt_addr,
 168                                  arch_kgdb_ops.gdb_bpt_instr, BREAK_INSTR_SIZE);
 169         return err;
 170 }
 171 NOKPROBE_SYMBOL(kgdb_arch_set_breakpoint);
 172
 173 int __weak kgdb_arch_remove_breakpoint(struct kgdb_bkpt *bpt)
 174 {
 175         return copy_to_kernel_nofault((char *)bpt->bpt_addr,
 176                                   (char *)bpt->saved_instr, BREAK_INSTR_SIZE);
 177 }
 178 NOKPROBE_SYMBOL(kgdb_arch_remove_breakpoint);
 179
 180 int __weak kgdb_validate_break_address(unsigned long addr)
 181 {
 182         struct kgdb_bkpt tmp;
 183         int err;
 184
 185         if (kgdb_within_blocklist(addr))
 186                 return -EINVAL;
 187
 188         /* Validate setting the breakpoint and then removing it.  If the
 189          * remove fails, the kernel needs to emit a bad message because we
 190          * are deep trouble not being able to put things back the way we
 191          * found them.
 192          */
 193         tmp.bpt_addr = addr;
 194         err = kgdb_arch_set_breakpoint(&tmp);
 195         if (err)
 196                 return err;
 197         err = kgdb_arch_remove_breakpoint(&tmp);
 198         if (err)
 199                 pr_err("Critical breakpoint error, kernel memory destroyed at: %lx\n",
 200                        addr);
 201         return err;
 202 }
 203
 204 unsigned long __weak kgdb_arch_pc(int exception, struct pt_regs *regs)
 205 {
 206         return instruction_pointer(regs);
 207 }
 208 NOKPROBE_SYMBOL(kgdb_arch_pc);
 209
 210 int __weak kgdb_arch_init(void)
 211 {
 212         return 0;
 213 }
 214
 215 int __weak kgdb_skipexception(int exception, struct pt_regs *regs)
 216 {
 217         return 0;
 218 }
 219 NOKPROBE_SYMBOL(kgdb_skipexception);
 220
 221 #ifdef CONFIG_SMP
 222
 223 /*
 224  * Default (weak) implementation for kgdb_roundup_cpus
 225  */
 226
 227 void __weak kgdb_call_nmi_hook(void *ignored)
 228 {
 229         /*
 230          * NOTE: get_irq_regs() is supposed to get the registers from
 231          * before the IPI interrupt happened and so is supposed to
 232          * show where the processor was.  In some situations it's
 233          * possible we might be called without an IPI, so it might be
 234          * safer to figure out how to make kgdb_breakpoint() work
 235          * properly here.
 236          */
 237         kgdb_nmicallback(raw_smp_processor_id(), get_irq_regs());
 238 }
 239 NOKPROBE_SYMBOL(kgdb_call_nmi_hook);
 240
 241 static DEFINE_PER_CPU(call_single_data_t, kgdb_roundup_csd) =
 242         CSD_INIT(kgdb_call_nmi_hook, NULL);
 243
 244 void __weak kgdb_roundup_cpus(void)
 245 {
 246         call_single_data_t *csd;
 247         int this_cpu = raw_smp_processor_id();
 248         int cpu;
 249         int ret;
 250
 251         for_each_online_cpu(cpu) {
 252                 /* No need to roundup ourselves */
 253                 if (cpu == this_cpu)
 254                         continue;
 255
 256                 csd = &per_cpu(kgdb_roundup_csd, cpu);
 257
 258                 /*
 259                  * If it didn't round up last time, don't try again
 260                  * since smp_call_function_single_async() will block.
 261                  *
 262                  * If rounding_up is false then we know that the
 263                  * previous call must have at least started and that
 264                  * means smp_call_function_single_async() won't block.
 265                  */
 266                 if (kgdb_info[cpu].rounding_up)
 267                         continue;
 268                 kgdb_info[cpu].rounding_up = true;
 269
 270                 ret = smp_call_function_single_async(cpu, csd);
 271                 if (ret)
 272                         kgdb_info[cpu].rounding_up = false;
 273         }
 274 }
 275 NOKPROBE_SYMBOL(kgdb_roundup_cpus);
 276
 277 #endif
 278
 279 /*
 280  * Some architectures need cache flushes when we set/clear a
 281  * breakpoint:
 282  */
 283 static void kgdb_flush_swbreak_addr(unsigned long addr)
 284 {
 285         if (!CACHE_FLUSH_IS_SAFE)
 286                 return;
 287
 288         if (current->mm) {
 289                 int i;
 290
 291                 for (i = 0; i < VMACACHE_SIZE; i++) {
 292                         if (!current->vmacache.vmas[i])
 293                                 continue;
 294                         flush_cache_range(current->vmacache.vmas[i],
 295                                           addr, addr + BREAK_INSTR_SIZE);
 296                 }
 297         }
 298
 299         /* Force flush instruction cache if it was outside the mm */
 300         flush_icache_range(addr, addr + BREAK_INSTR_SIZE);
 301 }
 302 NOKPROBE_SYMBOL(kgdb_flush_swbreak_addr);
 303
 304 /*
 305  * SW breakpoint management:
 306  */
 307 int dbg_activate_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_SET)
 315                         continue;
 316
 317                 error = kgdb_arch_set_breakpoint(&kgdb_break[i]);
 318                 if (error) {
 319                         ret = error;
 320                         pr_info("BP install failed: %lx\n",
 321                                 kgdb_break[i].bpt_addr);
 322                         continue;
 323                 }
 324
 325                 kgdb_flush_swbreak_addr(kgdb_break[i].bpt_addr);
 326                 kgdb_break[i].state = BP_ACTIVE;
 327         }
 328         return ret;
 329 }
 330 NOKPROBE_SYMBOL(dbg_activate_sw_breakpoints);
 331
 332 int dbg_set_sw_break(unsigned long addr)
 333 {
 334         int err = kgdb_validate_break_address(addr);
 335         int breakno = -1;
 336         int i;
 337
 338         if (err)
 339                 return err;
 340
 341         for (i = 0; i < KGDB_MAX_BREAKPOINTS; i++) {
 342                 if ((kgdb_break[i].state == BP_SET) &&
 343                                         (kgdb_break[i].bpt_addr == addr))
 344                         return -EEXIST;
 345         }
 346         for (i = 0; i < KGDB_MAX_BREAKPOINTS; i++) {
 347                 if (kgdb_break[i].state == BP_REMOVED &&
 348                                         kgdb_break[i].bpt_addr == addr) {
 349                         breakno = i;
 350                         break;
 351                 }
 352         }
 353
 354         if (breakno == -1) {
 355                 for (i = 0; i < KGDB_MAX_BREAKPOINTS; i++) {
 356                         if (kgdb_break[i].state == BP_UNDEFINED) {
 357                                 breakno = i;
 358                                 break;
 359                         }
 360                 }
 361         }
 362
 363         if (breakno == -1)
 364                 return -E2BIG;
 365
 366         kgdb_break[breakno].state = BP_SET;
 367         kgdb_break[breakno].type = BP_BREAKPOINT;
 368         kgdb_break[breakno].bpt_addr = addr;
 369
 370         return 0;
 371 }
 372
 373 int dbg_deactivate_sw_breakpoints(void)
 374 {
 375         int error;
 376         int ret = 0;
 377         int i;
 378
 379         for (i = 0; i < KGDB_MAX_BREAKPOINTS; i++) {
 380                 if (kgdb_break[i].state != BP_ACTIVE)
 381                         continue;
 382                 error = kgdb_arch_remove_breakpoint(&kgdb_break[i]);
 383                 if (error) {
 384                         pr_info("BP remove failed: %lx\n",
 385                                 kgdb_break[i].bpt_addr);
 386                         ret = error;
 387                 }
 388
 389                 kgdb_flush_swbreak_addr(kgdb_break[i].bpt_addr);
 390                 kgdb_break[i].state = BP_SET;
 391         }
 392         return ret;
 393 }
 394 NOKPROBE_SYMBOL(dbg_deactivate_sw_breakpoints);
 395
 396 int dbg_remove_sw_break(unsigned long addr)
 397 {
 398         int i;
 399
 400         for (i = 0; i < KGDB_MAX_BREAKPOINTS; i++) {
 401                 if ((kgdb_break[i].state == BP_SET) &&
 402                                 (kgdb_break[i].bpt_addr == addr)) {
 403                         kgdb_break[i].state = BP_REMOVED;
 404                         return 0;
 405                 }
 406         }
 407         return -ENOENT;
 408 }
 409
 410 int kgdb_isremovedbreak(unsigned long addr)
 411 {
 412         int i;
 413
 414         for (i = 0; i < KGDB_MAX_BREAKPOINTS; i++) {
 415                 if ((kgdb_break[i].state == BP_REMOVED) &&
 416                                         (kgdb_break[i].bpt_addr == addr))
 417                         return 1;
 418         }
 419         return 0;
 420 }
 421
 422 int kgdb_has_hit_break(unsigned long addr)
 423 {
 424         int i;
 425
 426         for (i = 0; i < KGDB_MAX_BREAKPOINTS; i++) {
 427                 if (kgdb_break[i].state == BP_ACTIVE &&
 428                     kgdb_break[i].bpt_addr == addr)
 429                         return 1;
 430         }
 431         return 0;
 432 }
 433
 434 int dbg_remove_all_break(void)
 435 {
 436         int error;
 437         int i;
 438
 439         /* Clear memory breakpoints. */
 440         for (i = 0; i < KGDB_MAX_BREAKPOINTS; i++) {
 441                 if (kgdb_break[i].state != BP_ACTIVE)
 442                         goto setundefined;
 443                 error = kgdb_arch_remove_breakpoint(&kgdb_break[i]);
 444                 if (error)
 445                         pr_err("breakpoint remove failed: %lx\n",
 446                                kgdb_break[i].bpt_addr);
 447 setundefined:
 448                 kgdb_break[i].state = BP_UNDEFINED;
 449         }
 450
 451         /* Clear hardware breakpoints. */
 452         if (arch_kgdb_ops.remove_all_hw_break)
 453                 arch_kgdb_ops.remove_all_hw_break();
 454
 455         return 0;
 456 }
 457
 458 void kgdb_free_init_mem(void)
 459 {
 460         int i;
 461
 462         /* Clear init memory breakpoints. */
 463         for (i = 0; i < KGDB_MAX_BREAKPOINTS; i++) {
 464                 if (init_section_contains((void *)kgdb_break[i].bpt_addr, 0))
 465                         kgdb_break[i].state = BP_UNDEFINED;
 466         }
 467 }
 468
 469 #ifdef CONFIG_KGDB_KDB
 470 void kdb_dump_stack_on_cpu(int cpu)
 471 {
 472         if (cpu == raw_smp_processor_id() || !IS_ENABLED(CONFIG_SMP)) {
 473                 dump_stack();
 474                 return;
 475         }
 476
 477         if (!(kgdb_info[cpu].exception_state & DCPU_IS_SLAVE)) {
 478                 kdb_printf("ERROR: Task on cpu %d didn't stop in the debugger\n",
 479                            cpu);
 480                 return;
 481         }
 482
 483         /*
 484          * In general, architectures don't support dumping the stack of a
 485          * "running" process that's not the current one.  From the point of
 486          * view of the Linux, kernel processes that are looping in the kgdb
 487          * slave loop are still "running".  There's also no API (that actually
 488          * works across all architectures) that can do a stack crawl based
 489          * on registers passed as a parameter.
 490          *
 491          * Solve this conundrum by asking slave CPUs to do the backtrace
 492          * themselves.
 493          */
 494         kgdb_info[cpu].exception_state |= DCPU_WANT_BT;
 495         while (kgdb_info[cpu].exception_state & DCPU_WANT_BT)
 496                 cpu_relax();
 497 }
 498 #endif
 499
 500 /*
 501  * Return true if there is a valid kgdb I/O module.  Also if no
 502  * debugger is attached a message can be printed to the console about
 503  * waiting for the debugger to attach.
 504  *
 505  * The print_wait argument is only to be true when called from inside
 506  * the core kgdb_handle_exception, because it will wait for the
 507  * debugger to attach.
 508  */
 509 static int kgdb_io_ready(int print_wait)
 510 {
 511         if (!dbg_io_ops)
 512                 return 0;
 513         if (kgdb_connected)
 514                 return 1;
 515         if (atomic_read(&kgdb_setting_breakpoint))
 516                 return 1;
 517         if (print_wait) {
 518 #ifdef CONFIG_KGDB_KDB
 519                 if (!dbg_kdb_mode)
 520                         pr_crit("waiting... or $3#33 for KDB\n");
 521 #else
 522                 pr_crit("Waiting for remote debugger\n");
 523 #endif
 524         }
 525         return 1;
 526 }
 527 NOKPROBE_SYMBOL(kgdb_io_ready);
 528
 529 static int kgdb_reenter_check(struct kgdb_state *ks)
 530 {
 531         unsigned long addr;
 532
 533         if (atomic_read(&kgdb_active) != raw_smp_processor_id())
 534                 return 0;
 535
 536         /* Panic on recursive debugger calls: */
 537         exception_level++;
 538         addr = kgdb_arch_pc(ks->ex_vector, ks->linux_regs);
 539         dbg_deactivate_sw_breakpoints();
 540
 541         /*
 542          * If the break point removed ok at the place exception
 543          * occurred, try to recover and print a warning to the end
 544          * user because the user planted a breakpoint in a place that
 545          * KGDB needs in order to function.
 546          */
 547         if (dbg_remove_sw_break(addr) == 0) {
 548                 exception_level = 0;
 549                 kgdb_skipexception(ks->ex_vector, ks->linux_regs);
 550                 dbg_activate_sw_breakpoints();
 551                 pr_crit("re-enter error: breakpoint removed %lx\n", addr);
 552                 WARN_ON_ONCE(1);
 553
 554                 return 1;
 555         }
 556         dbg_remove_all_break();
 557         kgdb_skipexception(ks->ex_vector, ks->linux_regs);
 558
 559         if (exception_level > 1) {
 560                 dump_stack();
 561                 kgdb_io_module_registered = false;
 562                 panic("Recursive entry to debugger");
 563         }
 564
 565         pr_crit("re-enter exception: ALL breakpoints killed\n");
 566 #ifdef CONFIG_KGDB_KDB
 567         /* Allow kdb to debug itself one level */
 568         return 0;
 569 #endif
 570         dump_stack();
 571         panic("Recursive entry to debugger");
 572
 573         return 1;
 574 }
 575 NOKPROBE_SYMBOL(kgdb_reenter_check);
 576
 577 static void dbg_touch_watchdogs(void)
 578 {
 579         touch_softlockup_watchdog_sync();
 580         clocksource_touch_watchdog();
 581         rcu_cpu_stall_reset();
 582 }
 583 NOKPROBE_SYMBOL(dbg_touch_watchdogs);
 584
 585 static int kgdb_cpu_enter(struct kgdb_state *ks, struct pt_regs *regs,
 586                 int exception_state)
 587 {
 588         unsigned long flags;
 589         int sstep_tries = 100;
 590         int error;
 591         int cpu;
 592         int trace_on = 0;
 593         int online_cpus = num_online_cpus();
 594         u64 time_left;
 595
 596         kgdb_info[ks->cpu].enter_kgdb++;
 597         kgdb_info[ks->cpu].exception_state |= exception_state;
 598
 599         if (exception_state == DCPU_WANT_MASTER)
 600                 atomic_inc(&masters_in_kgdb);
 601         else
 602                 atomic_inc(&slaves_in_kgdb);
 603
 604         if (arch_kgdb_ops.disable_hw_break)
 605                 arch_kgdb_ops.disable_hw_break(regs);
 606
 607 acquirelock:
 608         rcu_read_lock();
 609         /*
 610          * Interrupts will be restored by the 'trap return' code, except when
 611          * single stepping.
 612          */
 613         local_irq_save(flags);
 614
 615         cpu = ks->cpu;
 616         kgdb_info[cpu].debuggerinfo = regs;
 617         kgdb_info[cpu].task = current;
 618         kgdb_info[cpu].ret_state = 0;
 619         kgdb_info[cpu].irq_depth = hardirq_count() >> HARDIRQ_SHIFT;
 620
 621         /* Make sure the above info reaches the primary CPU */
 622         smp_mb();
 623
 624         if (exception_level == 1) {
 625                 if (raw_spin_trylock(&dbg_master_lock))
 626                         atomic_xchg(&kgdb_active, cpu);
 627                 goto cpu_master_loop;
 628         }
 629
 630         /*
 631          * CPU will loop if it is a slave or request to become a kgdb
 632          * master cpu and acquire the kgdb_active lock:
 633          */
 634         while (1) {
 635 cpu_loop:
 636                 if (kgdb_info[cpu].exception_state & DCPU_NEXT_MASTER) {
 637                         kgdb_info[cpu].exception_state &= ~DCPU_NEXT_MASTER;
 638                         goto cpu_master_loop;
 639                 } else if (kgdb_info[cpu].exception_state & DCPU_WANT_MASTER) {
 640                         if (raw_spin_trylock(&dbg_master_lock)) {
 641                                 atomic_xchg(&kgdb_active, cpu);
 642                                 break;
 643                         }
 644                 } else if (kgdb_info[cpu].exception_state & DCPU_WANT_BT) {
 645                         dump_stack();
 646                         kgdb_info[cpu].exception_state &= ~DCPU_WANT_BT;
 647                 } else if (kgdb_info[cpu].exception_state & DCPU_IS_SLAVE) {
 648                         if (!raw_spin_is_locked(&dbg_slave_lock))
 649                                 goto return_normal;
 650                 } else {
 651 return_normal:
 652                         /* Return to normal operation by executing any
 653                          * hw breakpoint fixup.
 654                          */
 655                         if (arch_kgdb_ops.correct_hw_break)
 656                                 arch_kgdb_ops.correct_hw_break();
 657                         if (trace_on)
 658                                 tracing_on();
 659                         kgdb_info[cpu].debuggerinfo = NULL;
 660                         kgdb_info[cpu].task = NULL;
 661                         kgdb_info[cpu].exception_state &=
 662                                 ~(DCPU_WANT_MASTER | DCPU_IS_SLAVE);
 663                         kgdb_info[cpu].enter_kgdb--;
 664                         smp_mb__before_atomic();
 665                         atomic_dec(&slaves_in_kgdb);
 666                         dbg_touch_watchdogs();
 667                         local_irq_restore(flags);
 668                         rcu_read_unlock();
 669                         return 0;
 670                 }
 671                 cpu_relax();
 672         }
 673
 674         /*
 675          * For single stepping, try to only enter on the processor
 676          * that was single stepping.  To guard against a deadlock, the
 677          * kernel will only try for the value of sstep_tries before
 678          * giving up and continuing on.
 679          */
 680         if (atomic_read(&kgdb_cpu_doing_single_step) != -1 &&
 681             (kgdb_info[cpu].task &&
 682              kgdb_info[cpu].task->pid != kgdb_sstep_pid) && --sstep_tries) {
 683                 atomic_set(&kgdb_active, -1);
 684                 raw_spin_unlock(&dbg_master_lock);
 685                 dbg_touch_watchdogs();
 686                 local_irq_restore(flags);
 687                 rcu_read_unlock();
 688
 689                 goto acquirelock;
 690         }
 691
 692         if (!kgdb_io_ready(1)) {
 693                 kgdb_info[cpu].ret_state = 1;
 694                 goto kgdb_restore; /* No I/O connection, resume the system */
 695         }
 696
 697         /*
 698          * Don't enter if we have hit a removed breakpoint.
 699          */
 700         if (kgdb_skipexception(ks->ex_vector, ks->linux_regs))
 701                 goto kgdb_restore;
 702
 703         atomic_inc(&ignore_console_lock_warning);
 704
 705         /* Call the I/O driver's pre_exception routine */
 706         if (dbg_io_ops->pre_exception)
 707                 dbg_io_ops->pre_exception();
 708
 709         /*
 710          * Get the passive CPU lock which will hold all the non-primary
 711          * CPU in a spin state while the debugger is active
 712          */
 713         if (!kgdb_single_step)
 714                 raw_spin_lock(&dbg_slave_lock);
 715
 716 #ifdef CONFIG_SMP
 717         /* If send_ready set, slaves are already waiting */
 718         if (ks->send_ready)
 719                 atomic_set(ks->send_ready, 1);
 720
 721         /* Signal the other CPUs to enter kgdb_wait() */
 722         else if ((!kgdb_single_step) && kgdb_do_roundup)
 723                 kgdb_roundup_cpus();
 724 #endif
 725
 726         /*
 727          * Wait for the other CPUs to be notified and be waiting for us:
 728          */
 729         time_left = MSEC_PER_SEC;
 730         while (kgdb_do_roundup && --time_left &&
 731                (atomic_read(&masters_in_kgdb) + atomic_read(&slaves_in_kgdb)) !=
 732                    online_cpus)
 733                 udelay(1000);
 734         if (!time_left)
 735                 pr_crit("Timed out waiting for secondary CPUs.\n");
 736
 737         /*
 738          * At this point the primary processor is completely
 739          * in the debugger and all secondary CPUs are quiescent
 740          */
 741         dbg_deactivate_sw_breakpoints();
 742         kgdb_single_step = 0;
 743         kgdb_contthread = current;
 744         exception_level = 0;
 745         trace_on = tracing_is_on();
 746         if (trace_on)
 747                 tracing_off();
 748
 749         while (1) {
 750 cpu_master_loop:
 751                 if (dbg_kdb_mode) {
 752                         kgdb_connected = 1;
 753                         error = kdb_stub(ks);
 754                         if (error == -1)
 755                                 continue;
 756                         kgdb_connected = 0;
 757                 } else {
 758                         error = gdb_serial_stub(ks);
 759                 }
 760
 761                 if (error == DBG_PASS_EVENT) {
 762                         dbg_kdb_mode = !dbg_kdb_mode;
 763                 } else if (error == DBG_SWITCH_CPU_EVENT) {
 764                         kgdb_info[dbg_switch_cpu].exception_state |=
 765                                 DCPU_NEXT_MASTER;
 766                         goto cpu_loop;
 767                 } else {
 768                         kgdb_info[cpu].ret_state = error;
 769                         break;
 770                 }
 771         }
 772
 773         dbg_activate_sw_breakpoints();
 774
 775         /* Call the I/O driver's post_exception routine */
 776         if (dbg_io_ops->post_exception)
 777                 dbg_io_ops->post_exception();
 778
 779         atomic_dec(&ignore_console_lock_warning);
 780
 781         if (!kgdb_single_step) {
 782                 raw_spin_unlock(&dbg_slave_lock);
 783                 /* Wait till all the CPUs have quit from the debugger. */
 784                 while (kgdb_do_roundup && atomic_read(&slaves_in_kgdb))
 785                         cpu_relax();
 786         }
 787
 788 kgdb_restore:
 789         if (atomic_read(&kgdb_cpu_doing_single_step) != -1) {
 790                 int sstep_cpu = atomic_read(&kgdb_cpu_doing_single_step);
 791                 if (kgdb_info[sstep_cpu].task)
 792                         kgdb_sstep_pid = kgdb_info[sstep_cpu].task->pid;
 793                 else
 794                         kgdb_sstep_pid = 0;
 795         }
 796         if (arch_kgdb_ops.correct_hw_break)
 797                 arch_kgdb_ops.correct_hw_break();
 798         if (trace_on)
 799                 tracing_on();
 800
 801         kgdb_info[cpu].debuggerinfo = NULL;
 802         kgdb_info[cpu].task = NULL;
 803         kgdb_info[cpu].exception_state &=
 804                 ~(DCPU_WANT_MASTER | DCPU_IS_SLAVE);
 805         kgdb_info[cpu].enter_kgdb--;
 806         smp_mb__before_atomic();
 807         atomic_dec(&masters_in_kgdb);
 808         /* Free kgdb_active */
 809         atomic_set(&kgdb_active, -1);
 810         raw_spin_unlock(&dbg_master_lock);
 811         dbg_touch_watchdogs();
 812         local_irq_restore(flags);
 813         rcu_read_unlock();
 814
 815         return kgdb_info[cpu].ret_state;
 816 }
 817 NOKPROBE_SYMBOL(kgdb_cpu_enter);
 818
 819 /*
 820  * kgdb_handle_exception() - main entry point from a kernel exception
 821  *
 822  * Locking hierarchy:
 823  *      interface locks, if any (begin_session)
 824  *      kgdb lock (kgdb_active)
 825  */
 826 int
 827 kgdb_handle_exception(int evector, int signo, int ecode, struct pt_regs *regs)
 828 {
 829         struct kgdb_state kgdb_var;
 830         struct kgdb_state *ks = &kgdb_var;
 831         int ret = 0;
 832
 833         if (arch_kgdb_ops.enable_nmi)
 834                 arch_kgdb_ops.enable_nmi(0);
 835         /*
 836          * Avoid entering the debugger if we were triggered due to an oops
 837          * but panic_timeout indicates the system should automatically
 838          * reboot on panic. We don't want to get stuck waiting for input
 839          * on such systems, especially if its "just" an oops.
 840          */
 841         if (signo != SIGTRAP && panic_timeout)
 842                 return 1;
 843
 844         memset(ks, 0, sizeof(struct kgdb_state));
 845         ks->cpu                 = raw_smp_processor_id();
 846         ks->ex_vector           = evector;
 847         ks->signo               = signo;
 848         ks->err_code            = ecode;
 849         ks->linux_regs          = regs;
 850
 851         if (kgdb_reenter_check(ks))
 852                 goto out; /* Ouch, double exception ! */
 853         if (kgdb_info[ks->cpu].enter_kgdb != 0)
 854                 goto out;
 855
 856         ret = kgdb_cpu_enter(ks, regs, DCPU_WANT_MASTER);
 857 out:
 858         if (arch_kgdb_ops.enable_nmi)
 859                 arch_kgdb_ops.enable_nmi(1);
 860         return ret;
 861 }
 862 NOKPROBE_SYMBOL(kgdb_handle_exception);
 863
 864 /*
 865  * GDB places a breakpoint at this function to know dynamically loaded objects.
 866  */
 867 static int module_event(struct notifier_block *self, unsigned long val,
 868         void *data)
 869 {
 870         return 0;
 871 }
 872
 873 static struct notifier_block dbg_module_load_nb = {
 874         .notifier_call  = module_event,
 875 };
 876
 877 int kgdb_nmicallback(int cpu, void *regs)
 878 {
 879 #ifdef CONFIG_SMP
 880         struct kgdb_state kgdb_var;
 881         struct kgdb_state *ks = &kgdb_var;
 882
 883         kgdb_info[cpu].rounding_up = false;
 884
 885         memset(ks, 0, sizeof(struct kgdb_state));
 886         ks->cpu                 = cpu;
 887         ks->linux_regs          = regs;
 888
 889         if (kgdb_info[ks->cpu].enter_kgdb == 0 &&
 890                         raw_spin_is_locked(&dbg_master_lock)) {
 891                 kgdb_cpu_enter(ks, regs, DCPU_IS_SLAVE);
 892                 return 0;
 893         }
 894 #endif
 895         return 1;
 896 }
 897 NOKPROBE_SYMBOL(kgdb_nmicallback);
 898
 899 int kgdb_nmicallin(int cpu, int trapnr, void *regs, int err_code,
 900                                                         atomic_t *send_ready)
 901 {
 902 #ifdef CONFIG_SMP
 903         if (!kgdb_io_ready(0) || !send_ready)
 904                 return 1;
 905
 906         if (kgdb_info[cpu].enter_kgdb == 0) {
 907                 struct kgdb_state kgdb_var;
 908                 struct kgdb_state *ks = &kgdb_var;
 909
 910                 memset(ks, 0, sizeof(struct kgdb_state));
 911                 ks->cpu                 = cpu;
 912                 ks->ex_vector           = trapnr;
 913                 ks->signo               = SIGTRAP;
 914                 ks->err_code            = err_code;
 915                 ks->linux_regs          = regs;
 916                 ks->send_ready          = send_ready;
 917                 kgdb_cpu_enter(ks, regs, DCPU_WANT_MASTER);
 918                 return 0;
 919         }
 920 #endif
 921         return 1;
 922 }
 923 NOKPROBE_SYMBOL(kgdb_nmicallin);
 924
 925 static void kgdb_console_write(struct console *co, const char *s,
 926    unsigned count)
 927 {
 928         unsigned long flags;
 929
 930         /* If we're debugging, or KGDB has not connected, don't try
 931          * and print. */
 932         if (!kgdb_connected || atomic_read(&kgdb_active) != -1 || dbg_kdb_mode)
 933                 return;
 934
 935         local_irq_save(flags);
 936         gdbstub_msg_write(s, count);
 937         local_irq_restore(flags);
 938 }
 939
 940 static struct console kgdbcons = {
 941         .name           = "kgdb",
 942         .write          = kgdb_console_write,
 943         .flags          = CON_PRINTBUFFER | CON_ENABLED,
 944         .index          = -1,
 945 };
 946
 947 static int __init opt_kgdb_con(char *str)
 948 {
 949         kgdb_use_con = 1;
 950
 951         if (kgdb_io_module_registered && !kgdb_con_registered) {
 952                 register_console(&kgdbcons);
 953                 kgdb_con_registered = 1;
 954         }
 955
 956         return 0;
 957 }
 958
 959 early_param("kgdbcon", opt_kgdb_con);
 960
 961 #ifdef CONFIG_MAGIC_SYSRQ
 962 static void sysrq_handle_dbg(int key)
 963 {
 964         if (!dbg_io_ops) {
 965                 pr_crit("ERROR: No KGDB I/O module available\n");
 966                 return;
 967         }
 968         if (!kgdb_connected) {
 969 #ifdef CONFIG_KGDB_KDB
 970                 if (!dbg_kdb_mode)
 971                         pr_crit("KGDB or $3#33 for KDB\n");
 972 #else
 973                 pr_crit("Entering KGDB\n");
 974 #endif
 975         }
 976
 977         kgdb_breakpoint();
 978 }
 979
 980 static const struct sysrq_key_op sysrq_dbg_op = {
 981         .handler        = sysrq_handle_dbg,
 982         .help_msg       = "debug(g)",
 983         .action_msg     = "DEBUG",
 984 };
 985 #endif
 986
 987 void kgdb_panic(const char *msg)
 988 {
 989         if (!kgdb_io_module_registered)
 990                 return;
 991
 992         /*
 993          * We don't want to get stuck waiting for input from user if
 994          * "panic_timeout" indicates the system should automatically
 995          * reboot on panic.
 996          */
 997         if (panic_timeout)
 998                 return;
 999
1000         if (dbg_kdb_mode)
1001                 kdb_printf("PANIC: %s\n", msg);
1002
1003         kgdb_breakpoint();
1004 }
1005
1006 static void kgdb_initial_breakpoint(void)
1007 {
1008         kgdb_break_asap = 0;
1009
1010         pr_crit("Waiting for connection from remote gdb...\n");
1011         kgdb_breakpoint();
1012 }
1013
1014 void __weak kgdb_arch_late(void)
1015 {
1016 }
1017
1018 void __init dbg_late_init(void)
1019 {
1020         dbg_is_early = false;
1021         if (kgdb_io_module_registered)
1022                 kgdb_arch_late();
1023         kdb_init(KDB_INIT_FULL);
1024
1025         if (kgdb_io_module_registered && kgdb_break_asap)
1026                 kgdb_initial_breakpoint();
1027 }
1028
1029 static int
1030 dbg_notify_reboot(struct notifier_block *this, unsigned long code, void *x)
1031 {
1032         /*
1033          * Take the following action on reboot notify depending on value:
1034          *    1 == Enter debugger
1035          *    0 == [the default] detach debug client
1036          *   -1 == Do nothing... and use this until the board resets
1037          */
1038         switch (kgdbreboot) {
1039         case 1:
1040                 kgdb_breakpoint();
1041                 goto done;
1042         case -1:
1043                 goto done;
1044         }
1045         if (!dbg_kdb_mode)
1046                 gdbstub_exit(code);
1047 done:
1048         return NOTIFY_DONE;
1049 }
1050
1051 static struct notifier_block dbg_reboot_notifier = {
1052         .notifier_call          = dbg_notify_reboot,
1053         .next                   = NULL,
1054         .priority               = INT_MAX,
1055 };
1056
1057 static void kgdb_register_callbacks(void)
1058 {
1059         if (!kgdb_io_module_registered) {
1060                 kgdb_io_module_registered = 1;
1061                 kgdb_arch_init();
1062                 if (!dbg_is_early)
1063                         kgdb_arch_late();
1064                 register_module_notifier(&dbg_module_load_nb);
1065                 register_reboot_notifier(&dbg_reboot_notifier);
1066 #ifdef CONFIG_MAGIC_SYSRQ
1067                 register_sysrq_key('g', &sysrq_dbg_op);
1068 #endif
1069                 if (kgdb_use_con && !kgdb_con_registered) {
1070                         register_console(&kgdbcons);
1071                         kgdb_con_registered = 1;
1072                 }
1073         }
1074 }
1075
1076 static void kgdb_unregister_callbacks(void)
1077 {
1078         /*
1079          * When this routine is called KGDB should unregister from
1080          * handlers and clean up, making sure it is not handling any
1081          * break exceptions at the time.
1082          */
1083         if (kgdb_io_module_registered) {
1084                 kgdb_io_module_registered = 0;
1085                 unregister_reboot_notifier(&dbg_reboot_notifier);
1086                 unregister_module_notifier(&dbg_module_load_nb);
1087                 kgdb_arch_exit();
1088 #ifdef CONFIG_MAGIC_SYSRQ
1089                 unregister_sysrq_key('g', &sysrq_dbg_op);
1090 #endif
1091                 if (kgdb_con_registered) {
1092                         unregister_console(&kgdbcons);
1093                         kgdb_con_registered = 0;
1094                 }
1095         }
1096 }
1097
1098 /**
1099  *      kgdb_register_io_module - register KGDB IO module
1100  *      @new_dbg_io_ops: the io ops vector
1101  *
1102  *      Register it with the KGDB core.
1103  */
1104 int kgdb_register_io_module(struct kgdb_io *new_dbg_io_ops)
1105 {
1106         struct kgdb_io *old_dbg_io_ops;
1107         int err;
1108
1109         spin_lock(&kgdb_registration_lock);
1110
1111         old_dbg_io_ops = dbg_io_ops;
1112         if (old_dbg_io_ops) {
1113                 if (!old_dbg_io_ops->deinit) {
1114                         spin_unlock(&kgdb_registration_lock);
1115
1116                         pr_err("KGDB I/O driver %s can't replace %s.\n",
1117                                 new_dbg_io_ops->name, old_dbg_io_ops->name);
1118                         return -EBUSY;
1119                 }
1120                 pr_info("Replacing I/O driver %s with %s\n",
1121                         old_dbg_io_ops->name, new_dbg_io_ops->name);
1122         }
1123
1124         if (new_dbg_io_ops->init) {
1125                 err = new_dbg_io_ops->init();
1126                 if (err) {
1127                         spin_unlock(&kgdb_registration_lock);
1128                         return err;
1129                 }
1130         }
1131
1132         dbg_io_ops = new_dbg_io_ops;
1133
1134         spin_unlock(&kgdb_registration_lock);
1135
1136         if (old_dbg_io_ops) {
1137                 old_dbg_io_ops->deinit();
1138                 return 0;
1139         }
1140
1141         pr_info("Registered I/O driver %s\n", new_dbg_io_ops->name);
1142
1143         /* Arm KGDB now. */
1144         kgdb_register_callbacks();
1145
1146         if (kgdb_break_asap &&
1147             (!dbg_is_early || IS_ENABLED(CONFIG_ARCH_HAS_EARLY_DEBUG)))
1148                 kgdb_initial_breakpoint();
1149
1150         return 0;
1151 }
1152 EXPORT_SYMBOL_GPL(kgdb_register_io_module);
1153
1154 /**
1155  *      kgdb_unregister_io_module - unregister KGDB IO module
1156  *      @old_dbg_io_ops: the io ops vector
1157  *
1158  *      Unregister it with the KGDB core.
1159  */
1160 void kgdb_unregister_io_module(struct kgdb_io *old_dbg_io_ops)
1161 {
1162         BUG_ON(kgdb_connected);
1163
1164         /*
1165          * KGDB is no longer able to communicate out, so
1166          * unregister our callbacks and reset state.
1167          */
1168         kgdb_unregister_callbacks();
1169
1170         spin_lock(&kgdb_registration_lock);
1171
1172         WARN_ON_ONCE(dbg_io_ops != old_dbg_io_ops);
1173         dbg_io_ops = NULL;
1174
1175         spin_unlock(&kgdb_registration_lock);
1176
1177         if (old_dbg_io_ops->deinit)
1178                 old_dbg_io_ops->deinit();
1179
1180         pr_info("Unregistered I/O driver %s, debugger disabled\n",
1181                 old_dbg_io_ops->name);
1182 }
1183 EXPORT_SYMBOL_GPL(kgdb_unregister_io_module);
1184
1185 int dbg_io_get_char(void)
1186 {
1187         int ret = dbg_io_ops->read_char();
1188         if (ret == NO_POLL_CHAR)
1189                 return -1;
1190         if (!dbg_kdb_mode)
1191                 return ret;
1192         if (ret == 127)
1193                 return 8;
1194         return ret;
1195 }
1196
1197 /**
1198  * kgdb_breakpoint - generate breakpoint exception
1199  *
1200  * This function will generate a breakpoint exception.  It is used at the
1201  * beginning of a program to sync up with a debugger and can be used
1202  * otherwise as a quick means to stop program execution and "break" into
1203  * the debugger.
1204  */
1205 noinline void kgdb_breakpoint(void)
1206 {
1207         atomic_inc(&kgdb_setting_breakpoint);
1208         wmb(); /* Sync point before breakpoint */
1209         arch_kgdb_breakpoint();
1210         wmb(); /* Sync point after breakpoint */
1211         atomic_dec(&kgdb_setting_breakpoint);
1212 }
1213 EXPORT_SYMBOL_GPL(kgdb_breakpoint);
1214
1215 static int __init opt_kgdb_wait(char *str)
1216 {
1217         kgdb_break_asap = 1;
1218
1219         kdb_init(KDB_INIT_EARLY);
1220         if (kgdb_io_module_registered &&
1221             IS_ENABLED(CONFIG_ARCH_HAS_EARLY_DEBUG))
1222                 kgdb_initial_breakpoint();
1223
1224         return 0;
1225 }
1226
1227 early_param("kgdbwait", opt_kgdb_wait);