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 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 overridden by architectures when needed:
 159  */
 160 int __weak kgdb_arch_set_breakpoint(struct kgdb_bkpt *bpt)
 161 {
 162         int err;
 163
 164         err = copy_from_kernel_nofault(bpt->saved_instr, (char *)bpt->bpt_addr,
 165                                 BREAK_INSTR_SIZE);
 166         if (err)
 167                 return err;
 168         err = copy_to_kernel_nofault((char *)bpt->bpt_addr,
 169                                  arch_kgdb_ops.gdb_bpt_instr, BREAK_INSTR_SIZE);
 170         return err;
 171 }
 172 NOKPROBE_SYMBOL(kgdb_arch_set_breakpoint);
 173
 174 int __weak kgdb_arch_remove_breakpoint(struct kgdb_bkpt *bpt)
 175 {
 176         return copy_to_kernel_nofault((char *)bpt->bpt_addr,
 177                                   (char *)bpt->saved_instr, BREAK_INSTR_SIZE);
 178 }
 179 NOKPROBE_SYMBOL(kgdb_arch_remove_breakpoint);
 180
 181 int __weak kgdb_validate_break_address(unsigned long addr)
 182 {
 183         struct kgdb_bkpt tmp;
 184         int err;
 185
 186         if (kgdb_within_blocklist(addr))
 187                 return -EINVAL;
 188
 189         /* Validate setting the breakpoint and then removing it.  If the
 190          * remove fails, the kernel needs to emit a bad message because we
 191          * are deep trouble not being able to put things back the way we
 192          * found them.
 193          */
 194         tmp.bpt_addr = addr;
 195         err = kgdb_arch_set_breakpoint(&tmp);
 196         if (err)
 197                 return err;
 198         err = kgdb_arch_remove_breakpoint(&tmp);
 199         if (err)
 200                 pr_err("Critical breakpoint error, kernel memory destroyed at: %lx\n",
 201                        addr);
 202         return err;
 203 }
 204
 205 unsigned long __weak kgdb_arch_pc(int exception, struct pt_regs *regs)
 206 {
 207         return instruction_pointer(regs);
 208 }
 209 NOKPROBE_SYMBOL(kgdb_arch_pc);
 210
 211 int __weak kgdb_arch_init(void)
 212 {
 213         return 0;
 214 }
 215
 216 int __weak kgdb_skipexception(int exception, struct pt_regs *regs)
 217 {
 218         return 0;
 219 }
 220 NOKPROBE_SYMBOL(kgdb_skipexception);
 221
 222 #ifdef CONFIG_SMP
 223
 224 /*
 225  * Default (weak) implementation for kgdb_roundup_cpus
 226  */
 227
 228 void __weak kgdb_call_nmi_hook(void *ignored)
 229 {
 230         /*
 231          * NOTE: get_irq_regs() is supposed to get the registers from
 232          * before the IPI interrupt happened and so is supposed to
 233          * show where the processor was.  In some situations it's
 234          * possible we might be called without an IPI, so it might be
 235          * safer to figure out how to make kgdb_breakpoint() work
 236          * properly here.
 237          */
 238         kgdb_nmicallback(raw_smp_processor_id(), get_irq_regs());
 239 }
 240 NOKPROBE_SYMBOL(kgdb_call_nmi_hook);
 241
 242 static DEFINE_PER_CPU(call_single_data_t, kgdb_roundup_csd) =
 243         CSD_INIT(kgdb_call_nmi_hook, NULL);
 244
 245 void __weak kgdb_roundup_cpus(void)
 246 {
 247         call_single_data_t *csd;
 248         int this_cpu = raw_smp_processor_id();
 249         int cpu;
 250         int ret;
 251
 252         for_each_online_cpu(cpu) {
 253                 /* No need to roundup ourselves */
 254                 if (cpu == this_cpu)
 255                         continue;
 256
 257                 csd = &per_cpu(kgdb_roundup_csd, cpu);
 258
 259                 /*
 260                  * If it didn't round up last time, don't try again
 261                  * since smp_call_function_single_async() will block.
 262                  *
 263                  * If rounding_up is false then we know that the
 264                  * previous call must have at least started and that
 265                  * means smp_call_function_single_async() won't block.
 266                  */
 267                 if (kgdb_info[cpu].rounding_up)
 268                         continue;
 269                 kgdb_info[cpu].rounding_up = true;
 270
 271                 ret = smp_call_function_single_async(cpu, csd);
 272                 if (ret)
 273                         kgdb_info[cpu].rounding_up = false;
 274         }
 275 }
 276 NOKPROBE_SYMBOL(kgdb_roundup_cpus);
 277
 278 #endif
 279
 280 /*
 281  * Some architectures need cache flushes when we set/clear a
 282  * breakpoint:
 283  */
 284 static void kgdb_flush_swbreak_addr(unsigned long addr)
 285 {
 286         if (!CACHE_FLUSH_IS_SAFE)
 287                 return;
 288
 289         if (current->mm) {
 290                 int i;
 291
 292                 for (i = 0; i < VMACACHE_SIZE; i++) {
 293                         if (!current->vmacache.vmas[i])
 294                                 continue;
 295                         flush_cache_range(current->vmacache.vmas[i],
 296                                           addr, addr + BREAK_INSTR_SIZE);
 297                 }
 298         }
 299
 300         /* Force flush instruction cache if it was outside the mm */
 301         flush_icache_range(addr, addr + BREAK_INSTR_SIZE);
 302 }
 303 NOKPROBE_SYMBOL(kgdb_flush_swbreak_addr);
 304
 305 /*
 306  * SW breakpoint management:
 307  */
 308 int dbg_activate_sw_breakpoints(void)
 309 {
 310         int error;
 311         int ret = 0;
 312         int i;
 313
 314         for (i = 0; i < KGDB_MAX_BREAKPOINTS; i++) {
 315                 if (kgdb_break[i].state != BP_SET)
 316                         continue;
 317
 318                 error = kgdb_arch_set_breakpoint(&kgdb_break[i]);
 319                 if (error) {
 320                         ret = error;
 321                         pr_info("BP install failed: %lx\n",
 322                                 kgdb_break[i].bpt_addr);
 323                         continue;
 324                 }
 325
 326                 kgdb_flush_swbreak_addr(kgdb_break[i].bpt_addr);
 327                 kgdb_break[i].state = BP_ACTIVE;
 328         }
 329         return ret;
 330 }
 331 NOKPROBE_SYMBOL(dbg_activate_sw_breakpoints);
 332
 333 int dbg_set_sw_break(unsigned long addr)
 334 {
 335         int err = kgdb_validate_break_address(addr);
 336         int breakno = -1;
 337         int i;
 338
 339         if (err)
 340                 return err;
 341
 342         for (i = 0; i < KGDB_MAX_BREAKPOINTS; i++) {
 343                 if ((kgdb_break[i].state == BP_SET) &&
 344                                         (kgdb_break[i].bpt_addr == addr))
 345                         return -EEXIST;
 346         }
 347         for (i = 0; i < KGDB_MAX_BREAKPOINTS; i++) {
 348                 if (kgdb_break[i].state == BP_REMOVED &&
 349                                         kgdb_break[i].bpt_addr == addr) {
 350                         breakno = i;
 351                         break;
 352                 }
 353         }
 354
 355         if (breakno == -1) {
 356                 for (i = 0; i < KGDB_MAX_BREAKPOINTS; i++) {
 357                         if (kgdb_break[i].state == BP_UNDEFINED) {
 358                                 breakno = i;
 359                                 break;
 360                         }
 361                 }
 362         }
 363
 364         if (breakno == -1)
 365                 return -E2BIG;
 366
 367         kgdb_break[breakno].state = BP_SET;
 368         kgdb_break[breakno].type = BP_BREAKPOINT;
 369         kgdb_break[breakno].bpt_addr = addr;
 370
 371         return 0;
 372 }
 373
 374 int dbg_deactivate_sw_breakpoints(void)
 375 {
 376         int error;
 377         int ret = 0;
 378         int i;
 379
 380         for (i = 0; i < KGDB_MAX_BREAKPOINTS; i++) {
 381                 if (kgdb_break[i].state != BP_ACTIVE)
 382                         continue;
 383                 error = kgdb_arch_remove_breakpoint(&kgdb_break[i]);
 384                 if (error) {
 385                         pr_info("BP remove failed: %lx\n",
 386                                 kgdb_break[i].bpt_addr);
 387                         ret = error;
 388                 }
 389
 390                 kgdb_flush_swbreak_addr(kgdb_break[i].bpt_addr);
 391                 kgdb_break[i].state = BP_SET;
 392         }
 393         return ret;
 394 }
 395 NOKPROBE_SYMBOL(dbg_deactivate_sw_breakpoints);
 396
 397 int dbg_remove_sw_break(unsigned long addr)
 398 {
 399         int i;
 400
 401         for (i = 0; i < KGDB_MAX_BREAKPOINTS; i++) {
 402                 if ((kgdb_break[i].state == BP_SET) &&
 403                                 (kgdb_break[i].bpt_addr == addr)) {
 404                         kgdb_break[i].state = BP_REMOVED;
 405                         return 0;
 406                 }
 407         }
 408         return -ENOENT;
 409 }
 410
 411 int kgdb_isremovedbreak(unsigned long addr)
 412 {
 413         int i;
 414
 415         for (i = 0; i < KGDB_MAX_BREAKPOINTS; i++) {
 416                 if ((kgdb_break[i].state == BP_REMOVED) &&
 417                                         (kgdb_break[i].bpt_addr == addr))
 418                         return 1;
 419         }
 420         return 0;
 421 }
 422
 423 int kgdb_has_hit_break(unsigned long addr)
 424 {
 425         int i;
 426
 427         for (i = 0; i < KGDB_MAX_BREAKPOINTS; i++) {
 428                 if (kgdb_break[i].state == BP_ACTIVE &&
 429                     kgdb_break[i].bpt_addr == addr)
 430                         return 1;
 431         }
 432         return 0;
 433 }
 434
 435 int dbg_remove_all_break(void)
 436 {
 437         int error;
 438         int i;
 439
 440         /* Clear memory breakpoints. */
 441         for (i = 0; i < KGDB_MAX_BREAKPOINTS; i++) {
 442                 if (kgdb_break[i].state != BP_ACTIVE)
 443                         goto setundefined;
 444                 error = kgdb_arch_remove_breakpoint(&kgdb_break[i]);
 445                 if (error)
 446                         pr_err("breakpoint remove failed: %lx\n",
 447                                kgdb_break[i].bpt_addr);
 448 setundefined:
 449                 kgdb_break[i].state = BP_UNDEFINED;
 450         }
 451
 452         /* Clear hardware breakpoints. */
 453         if (arch_kgdb_ops.remove_all_hw_break)
 454                 arch_kgdb_ops.remove_all_hw_break();
 455
 456         return 0;
 457 }
 458
 459 #ifdef CONFIG_KGDB_KDB
 460 void kdb_dump_stack_on_cpu(int cpu)
 461 {
 462         if (cpu == raw_smp_processor_id() || !IS_ENABLED(CONFIG_SMP)) {
 463                 dump_stack();
 464                 return;
 465         }
 466
 467         if (!(kgdb_info[cpu].exception_state & DCPU_IS_SLAVE)) {
 468                 kdb_printf("ERROR: Task on cpu %d didn't stop in the debugger\n",
 469                            cpu);
 470                 return;
 471         }
 472
 473         /*
 474          * In general, architectures don't support dumping the stack of a
 475          * "running" process that's not the current one.  From the point of
 476          * view of the Linux, kernel processes that are looping in the kgdb
 477          * slave loop are still "running".  There's also no API (that actually
 478          * works across all architectures) that can do a stack crawl based
 479          * on registers passed as a parameter.
 480          *
 481          * Solve this conundrum by asking slave CPUs to do the backtrace
 482          * themselves.
 483          */
 484         kgdb_info[cpu].exception_state |= DCPU_WANT_BT;
 485         while (kgdb_info[cpu].exception_state & DCPU_WANT_BT)
 486                 cpu_relax();
 487 }
 488 #endif
 489
 490 /*
 491  * Return true if there is a valid kgdb I/O module.  Also if no
 492  * debugger is attached a message can be printed to the console about
 493  * waiting for the debugger to attach.
 494  *
 495  * The print_wait argument is only to be true when called from inside
 496  * the core kgdb_handle_exception, because it will wait for the
 497  * debugger to attach.
 498  */
 499 static int kgdb_io_ready(int print_wait)
 500 {
 501         if (!dbg_io_ops)
 502                 return 0;
 503         if (kgdb_connected)
 504                 return 1;
 505         if (atomic_read(&kgdb_setting_breakpoint))
 506                 return 1;
 507         if (print_wait) {
 508 #ifdef CONFIG_KGDB_KDB
 509                 if (!dbg_kdb_mode)
 510                         pr_crit("waiting... or $3#33 for KDB\n");
 511 #else
 512                 pr_crit("Waiting for remote debugger\n");
 513 #endif
 514         }
 515         return 1;
 516 }
 517 NOKPROBE_SYMBOL(kgdb_io_ready);
 518
 519 static int kgdb_reenter_check(struct kgdb_state *ks)
 520 {
 521         unsigned long addr;
 522
 523         if (atomic_read(&kgdb_active) != raw_smp_processor_id())
 524                 return 0;
 525
 526         /* Panic on recursive debugger calls: */
 527         exception_level++;
 528         addr = kgdb_arch_pc(ks->ex_vector, ks->linux_regs);
 529         dbg_deactivate_sw_breakpoints();
 530
 531         /*
 532          * If the break point removed ok at the place exception
 533          * occurred, try to recover and print a warning to the end
 534          * user because the user planted a breakpoint in a place that
 535          * KGDB needs in order to function.
 536          */
 537         if (dbg_remove_sw_break(addr) == 0) {
 538                 exception_level = 0;
 539                 kgdb_skipexception(ks->ex_vector, ks->linux_regs);
 540                 dbg_activate_sw_breakpoints();
 541                 pr_crit("re-enter error: breakpoint removed %lx\n", addr);
 542                 WARN_ON_ONCE(1);
 543
 544                 return 1;
 545         }
 546         dbg_remove_all_break();
 547         kgdb_skipexception(ks->ex_vector, ks->linux_regs);
 548
 549         if (exception_level > 1) {
 550                 dump_stack();
 551                 kgdb_io_module_registered = false;
 552                 panic("Recursive entry to debugger");
 553         }
 554
 555         pr_crit("re-enter exception: ALL breakpoints killed\n");
 556 #ifdef CONFIG_KGDB_KDB
 557         /* Allow kdb to debug itself one level */
 558         return 0;
 559 #endif
 560         dump_stack();
 561         panic("Recursive entry to debugger");
 562
 563         return 1;
 564 }
 565 NOKPROBE_SYMBOL(kgdb_reenter_check);
 566
 567 static void dbg_touch_watchdogs(void)
 568 {
 569         touch_softlockup_watchdog_sync();
 570         clocksource_touch_watchdog();
 571         rcu_cpu_stall_reset();
 572 }
 573 NOKPROBE_SYMBOL(dbg_touch_watchdogs);
 574
 575 static int kgdb_cpu_enter(struct kgdb_state *ks, struct pt_regs *regs,
 576                 int exception_state)
 577 {
 578         unsigned long flags;
 579         int sstep_tries = 100;
 580         int error;
 581         int cpu;
 582         int trace_on = 0;
 583         int online_cpus = num_online_cpus();
 584         u64 time_left;
 585
 586         kgdb_info[ks->cpu].enter_kgdb++;
 587         kgdb_info[ks->cpu].exception_state |= exception_state;
 588
 589         if (exception_state == DCPU_WANT_MASTER)
 590                 atomic_inc(&masters_in_kgdb);
 591         else
 592                 atomic_inc(&slaves_in_kgdb);
 593
 594         if (arch_kgdb_ops.disable_hw_break)
 595                 arch_kgdb_ops.disable_hw_break(regs);
 596
 597 acquirelock:
 598         rcu_read_lock();
 599         /*
 600          * Interrupts will be restored by the 'trap return' code, except when
 601          * single stepping.
 602          */
 603         local_irq_save(flags);
 604
 605         cpu = ks->cpu;
 606         kgdb_info[cpu].debuggerinfo = regs;
 607         kgdb_info[cpu].task = current;
 608         kgdb_info[cpu].ret_state = 0;
 609         kgdb_info[cpu].irq_depth = hardirq_count() >> HARDIRQ_SHIFT;
 610
 611         /* Make sure the above info reaches the primary CPU */
 612         smp_mb();
 613
 614         if (exception_level == 1) {
 615                 if (raw_spin_trylock(&dbg_master_lock))
 616                         atomic_xchg(&kgdb_active, cpu);
 617                 goto cpu_master_loop;
 618         }
 619
 620         /*
 621          * CPU will loop if it is a slave or request to become a kgdb
 622          * master cpu and acquire the kgdb_active lock:
 623          */
 624         while (1) {
 625 cpu_loop:
 626                 if (kgdb_info[cpu].exception_state & DCPU_NEXT_MASTER) {
 627                         kgdb_info[cpu].exception_state &= ~DCPU_NEXT_MASTER;
 628                         goto cpu_master_loop;
 629                 } else if (kgdb_info[cpu].exception_state & DCPU_WANT_MASTER) {
 630                         if (raw_spin_trylock(&dbg_master_lock)) {
 631                                 atomic_xchg(&kgdb_active, cpu);
 632                                 break;
 633                         }
 634                 } else if (kgdb_info[cpu].exception_state & DCPU_WANT_BT) {
 635                         dump_stack();
 636                         kgdb_info[cpu].exception_state &= ~DCPU_WANT_BT;
 637                 } else if (kgdb_info[cpu].exception_state & DCPU_IS_SLAVE) {
 638                         if (!raw_spin_is_locked(&dbg_slave_lock))
 639                                 goto return_normal;
 640                 } else {
 641 return_normal:
 642                         /* Return to normal operation by executing any
 643                          * hw breakpoint fixup.
 644                          */
 645                         if (arch_kgdb_ops.correct_hw_break)
 646                                 arch_kgdb_ops.correct_hw_break();
 647                         if (trace_on)
 648                                 tracing_on();
 649                         kgdb_info[cpu].debuggerinfo = NULL;
 650                         kgdb_info[cpu].task = NULL;
 651                         kgdb_info[cpu].exception_state &=
 652                                 ~(DCPU_WANT_MASTER | DCPU_IS_SLAVE);
 653                         kgdb_info[cpu].enter_kgdb--;
 654                         smp_mb__before_atomic();
 655                         atomic_dec(&slaves_in_kgdb);
 656                         dbg_touch_watchdogs();
 657                         local_irq_restore(flags);
 658                         rcu_read_unlock();
 659                         return 0;
 660                 }
 661                 cpu_relax();
 662         }
 663
 664         /*
 665          * For single stepping, try to only enter on the processor
 666          * that was single stepping.  To guard against a deadlock, the
 667          * kernel will only try for the value of sstep_tries before
 668          * giving up and continuing on.
 669          */
 670         if (atomic_read(&kgdb_cpu_doing_single_step) != -1 &&
 671             (kgdb_info[cpu].task &&
 672              kgdb_info[cpu].task->pid != kgdb_sstep_pid) && --sstep_tries) {
 673                 atomic_set(&kgdb_active, -1);
 674                 raw_spin_unlock(&dbg_master_lock);
 675                 dbg_touch_watchdogs();
 676                 local_irq_restore(flags);
 677                 rcu_read_unlock();
 678
 679                 goto acquirelock;
 680         }
 681
 682         if (!kgdb_io_ready(1)) {
 683                 kgdb_info[cpu].ret_state = 1;
 684                 goto kgdb_restore; /* No I/O connection, resume the system */
 685         }
 686
 687         /*
 688          * Don't enter if we have hit a removed breakpoint.
 689          */
 690         if (kgdb_skipexception(ks->ex_vector, ks->linux_regs))
 691                 goto kgdb_restore;
 692
 693         atomic_inc(&ignore_console_lock_warning);
 694
 695         /* Call the I/O driver's pre_exception routine */
 696         if (dbg_io_ops->pre_exception)
 697                 dbg_io_ops->pre_exception();
 698
 699         /*
 700          * Get the passive CPU lock which will hold all the non-primary
 701          * CPU in a spin state while the debugger is active
 702          */
 703         if (!kgdb_single_step)
 704                 raw_spin_lock(&dbg_slave_lock);
 705
 706 #ifdef CONFIG_SMP
 707         /* If send_ready set, slaves are already waiting */
 708         if (ks->send_ready)
 709                 atomic_set(ks->send_ready, 1);
 710
 711         /* Signal the other CPUs to enter kgdb_wait() */
 712         else if ((!kgdb_single_step) && kgdb_do_roundup)
 713                 kgdb_roundup_cpus();
 714 #endif
 715
 716         /*
 717          * Wait for the other CPUs to be notified and be waiting for us:
 718          */
 719         time_left = MSEC_PER_SEC;
 720         while (kgdb_do_roundup && --time_left &&
 721                (atomic_read(&masters_in_kgdb) + atomic_read(&slaves_in_kgdb)) !=
 722                    online_cpus)
 723                 udelay(1000);
 724         if (!time_left)
 725                 pr_crit("Timed out waiting for secondary CPUs.\n");
 726
 727         /*
 728          * At this point the primary processor is completely
 729          * in the debugger and all secondary CPUs are quiescent
 730          */
 731         dbg_deactivate_sw_breakpoints();
 732         kgdb_single_step = 0;
 733         kgdb_contthread = current;
 734         exception_level = 0;
 735         trace_on = tracing_is_on();
 736         if (trace_on)
 737                 tracing_off();
 738
 739         while (1) {
 740 cpu_master_loop:
 741                 if (dbg_kdb_mode) {
 742                         kgdb_connected = 1;
 743                         error = kdb_stub(ks);
 744                         if (error == -1)
 745                                 continue;
 746                         kgdb_connected = 0;
 747                 } else {
 748                         error = gdb_serial_stub(ks);
 749                 }
 750
 751                 if (error == DBG_PASS_EVENT) {
 752                         dbg_kdb_mode = !dbg_kdb_mode;
 753                 } else if (error == DBG_SWITCH_CPU_EVENT) {
 754                         kgdb_info[dbg_switch_cpu].exception_state |=
 755                                 DCPU_NEXT_MASTER;
 756                         goto cpu_loop;
 757                 } else {
 758                         kgdb_info[cpu].ret_state = error;
 759                         break;
 760                 }
 761         }
 762
 763         dbg_activate_sw_breakpoints();
 764
 765         /* Call the I/O driver's post_exception routine */
 766         if (dbg_io_ops->post_exception)
 767                 dbg_io_ops->post_exception();
 768
 769         atomic_dec(&ignore_console_lock_warning);
 770
 771         if (!kgdb_single_step) {
 772                 raw_spin_unlock(&dbg_slave_lock);
 773                 /* Wait till all the CPUs have quit from the debugger. */
 774                 while (kgdb_do_roundup && atomic_read(&slaves_in_kgdb))
 775                         cpu_relax();
 776         }
 777
 778 kgdb_restore:
 779         if (atomic_read(&kgdb_cpu_doing_single_step) != -1) {
 780                 int sstep_cpu = atomic_read(&kgdb_cpu_doing_single_step);
 781                 if (kgdb_info[sstep_cpu].task)
 782                         kgdb_sstep_pid = kgdb_info[sstep_cpu].task->pid;
 783                 else
 784                         kgdb_sstep_pid = 0;
 785         }
 786         if (arch_kgdb_ops.correct_hw_break)
 787                 arch_kgdb_ops.correct_hw_break();
 788         if (trace_on)
 789                 tracing_on();
 790
 791         kgdb_info[cpu].debuggerinfo = NULL;
 792         kgdb_info[cpu].task = NULL;
 793         kgdb_info[cpu].exception_state &=
 794                 ~(DCPU_WANT_MASTER | DCPU_IS_SLAVE);
 795         kgdb_info[cpu].enter_kgdb--;
 796         smp_mb__before_atomic();
 797         atomic_dec(&masters_in_kgdb);
 798         /* Free kgdb_active */
 799         atomic_set(&kgdb_active, -1);
 800         raw_spin_unlock(&dbg_master_lock);
 801         dbg_touch_watchdogs();
 802         local_irq_restore(flags);
 803         rcu_read_unlock();
 804
 805         return kgdb_info[cpu].ret_state;
 806 }
 807 NOKPROBE_SYMBOL(kgdb_cpu_enter);
 808
 809 /*
 810  * kgdb_handle_exception() - main entry point from a kernel exception
 811  *
 812  * Locking hierarchy:
 813  *      interface locks, if any (begin_session)
 814  *      kgdb lock (kgdb_active)
 815  */
 816 int
 817 kgdb_handle_exception(int evector, int signo, int ecode, struct pt_regs *regs)
 818 {
 819         struct kgdb_state kgdb_var;
 820         struct kgdb_state *ks = &kgdb_var;
 821         int ret = 0;
 822
 823         if (arch_kgdb_ops.enable_nmi)
 824                 arch_kgdb_ops.enable_nmi(0);
 825         /*
 826          * Avoid entering the debugger if we were triggered due to an oops
 827          * but panic_timeout indicates the system should automatically
 828          * reboot on panic. We don't want to get stuck waiting for input
 829          * on such systems, especially if its "just" an oops.
 830          */
 831         if (signo != SIGTRAP && panic_timeout)
 832                 return 1;
 833
 834         memset(ks, 0, sizeof(struct kgdb_state));
 835         ks->cpu                 = raw_smp_processor_id();
 836         ks->ex_vector           = evector;
 837         ks->signo               = signo;
 838         ks->err_code            = ecode;
 839         ks->linux_regs          = regs;
 840
 841         if (kgdb_reenter_check(ks))
 842                 goto out; /* Ouch, double exception ! */
 843         if (kgdb_info[ks->cpu].enter_kgdb != 0)
 844                 goto out;
 845
 846         ret = kgdb_cpu_enter(ks, regs, DCPU_WANT_MASTER);
 847 out:
 848         if (arch_kgdb_ops.enable_nmi)
 849                 arch_kgdb_ops.enable_nmi(1);
 850         return ret;
 851 }
 852 NOKPROBE_SYMBOL(kgdb_handle_exception);
 853
 854 /*
 855  * GDB places a breakpoint at this function to know dynamically loaded objects.
 856  */
 857 static int module_event(struct notifier_block *self, unsigned long val,
 858         void *data)
 859 {
 860         return 0;
 861 }
 862
 863 static struct notifier_block dbg_module_load_nb = {
 864         .notifier_call  = module_event,
 865 };
 866
 867 int kgdb_nmicallback(int cpu, void *regs)
 868 {
 869 #ifdef CONFIG_SMP
 870         struct kgdb_state kgdb_var;
 871         struct kgdb_state *ks = &kgdb_var;
 872
 873         kgdb_info[cpu].rounding_up = false;
 874
 875         memset(ks, 0, sizeof(struct kgdb_state));
 876         ks->cpu                 = cpu;
 877         ks->linux_regs          = regs;
 878
 879         if (kgdb_info[ks->cpu].enter_kgdb == 0 &&
 880                         raw_spin_is_locked(&dbg_master_lock)) {
 881                 kgdb_cpu_enter(ks, regs, DCPU_IS_SLAVE);
 882                 return 0;
 883         }
 884 #endif
 885         return 1;
 886 }
 887 NOKPROBE_SYMBOL(kgdb_nmicallback);
 888
 889 int kgdb_nmicallin(int cpu, int trapnr, void *regs, int err_code,
 890                                                         atomic_t *send_ready)
 891 {
 892 #ifdef CONFIG_SMP
 893         if (!kgdb_io_ready(0) || !send_ready)
 894                 return 1;
 895
 896         if (kgdb_info[cpu].enter_kgdb == 0) {
 897                 struct kgdb_state kgdb_var;
 898                 struct kgdb_state *ks = &kgdb_var;
 899
 900                 memset(ks, 0, sizeof(struct kgdb_state));
 901                 ks->cpu                 = cpu;
 902                 ks->ex_vector           = trapnr;
 903                 ks->signo               = SIGTRAP;
 904                 ks->err_code            = err_code;
 905                 ks->linux_regs          = regs;
 906                 ks->send_ready          = send_ready;
 907                 kgdb_cpu_enter(ks, regs, DCPU_WANT_MASTER);
 908                 return 0;
 909         }
 910 #endif
 911         return 1;
 912 }
 913 NOKPROBE_SYMBOL(kgdb_nmicallin);
 914
 915 static void kgdb_console_write(struct console *co, const char *s,
 916    unsigned count)
 917 {
 918         unsigned long flags;
 919
 920         /* If we're debugging, or KGDB has not connected, don't try
 921          * and print. */
 922         if (!kgdb_connected || atomic_read(&kgdb_active) != -1 || dbg_kdb_mode)
 923                 return;
 924
 925         local_irq_save(flags);
 926         gdbstub_msg_write(s, count);
 927         local_irq_restore(flags);
 928 }
 929
 930 static struct console kgdbcons = {
 931         .name           = "kgdb",
 932         .write          = kgdb_console_write,
 933         .flags          = CON_PRINTBUFFER | CON_ENABLED,
 934         .index          = -1,
 935 };
 936
 937 static int __init opt_kgdb_con(char *str)
 938 {
 939         kgdb_use_con = 1;
 940
 941         if (kgdb_io_module_registered && !kgdb_con_registered) {
 942                 register_console(&kgdbcons);
 943                 kgdb_con_registered = 1;
 944         }
 945
 946         return 0;
 947 }
 948
 949 early_param("kgdbcon", opt_kgdb_con);
 950
 951 #ifdef CONFIG_MAGIC_SYSRQ
 952 static void sysrq_handle_dbg(int key)
 953 {
 954         if (!dbg_io_ops) {
 955                 pr_crit("ERROR: No KGDB I/O module available\n");
 956                 return;
 957         }
 958         if (!kgdb_connected) {
 959 #ifdef CONFIG_KGDB_KDB
 960                 if (!dbg_kdb_mode)
 961                         pr_crit("KGDB or $3#33 for KDB\n");
 962 #else
 963                 pr_crit("Entering KGDB\n");
 964 #endif
 965         }
 966
 967         kgdb_breakpoint();
 968 }
 969
 970 static const struct sysrq_key_op sysrq_dbg_op = {
 971         .handler        = sysrq_handle_dbg,
 972         .help_msg       = "debug(g)",
 973         .action_msg     = "DEBUG",
 974 };
 975 #endif
 976
 977 void kgdb_panic(const char *msg)
 978 {
 979         if (!kgdb_io_module_registered)
 980                 return;
 981
 982         /*
 983          * We don't want to get stuck waiting for input from user if
 984          * "panic_timeout" indicates the system should automatically
 985          * reboot on panic.
 986          */
 987         if (panic_timeout)
 988                 return;
 989
 990         if (dbg_kdb_mode)
 991                 kdb_printf("PANIC: %s\n", msg);
 992
 993         kgdb_breakpoint();
 994 }
 995
 996 static void kgdb_initial_breakpoint(void)
 997 {
 998         kgdb_break_asap = 0;
 999
1000         pr_crit("Waiting for connection from remote gdb...\n");
1001         kgdb_breakpoint();
1002 }
1003
1004 void __weak kgdb_arch_late(void)
1005 {
1006 }
1007
1008 void __init dbg_late_init(void)
1009 {
1010         dbg_is_early = false;
1011         if (kgdb_io_module_registered)
1012                 kgdb_arch_late();
1013         kdb_init(KDB_INIT_FULL);
1014
1015         if (kgdb_io_module_registered && kgdb_break_asap)
1016                 kgdb_initial_breakpoint();
1017 }
1018
1019 static int
1020 dbg_notify_reboot(struct notifier_block *this, unsigned long code, void *x)
1021 {
1022         /*
1023          * Take the following action on reboot notify depending on value:
1024          *    1 == Enter debugger
1025          *    0 == [the default] detatch debug client
1026          *   -1 == Do nothing... and use this until the board resets
1027          */
1028         switch (kgdbreboot) {
1029         case 1:
1030                 kgdb_breakpoint();
1031         case -1:
1032                 goto done;
1033         }
1034         if (!dbg_kdb_mode)
1035                 gdbstub_exit(code);
1036 done:
1037         return NOTIFY_DONE;
1038 }
1039
1040 static struct notifier_block dbg_reboot_notifier = {
1041         .notifier_call          = dbg_notify_reboot,
1042         .next                   = NULL,
1043         .priority               = INT_MAX,
1044 };
1045
1046 static void kgdb_register_callbacks(void)
1047 {
1048         if (!kgdb_io_module_registered) {
1049                 kgdb_io_module_registered = 1;
1050                 kgdb_arch_init();
1051                 if (!dbg_is_early)
1052                         kgdb_arch_late();
1053                 register_module_notifier(&dbg_module_load_nb);
1054                 register_reboot_notifier(&dbg_reboot_notifier);
1055 #ifdef CONFIG_MAGIC_SYSRQ
1056                 register_sysrq_key('g', &sysrq_dbg_op);
1057 #endif
1058                 if (kgdb_use_con && !kgdb_con_registered) {
1059                         register_console(&kgdbcons);
1060                         kgdb_con_registered = 1;
1061                 }
1062         }
1063 }
1064
1065 static void kgdb_unregister_callbacks(void)
1066 {
1067         /*
1068          * When this routine is called KGDB should unregister from
1069          * handlers and clean up, making sure it is not handling any
1070          * break exceptions at the time.
1071          */
1072         if (kgdb_io_module_registered) {
1073                 kgdb_io_module_registered = 0;
1074                 unregister_reboot_notifier(&dbg_reboot_notifier);
1075                 unregister_module_notifier(&dbg_module_load_nb);
1076                 kgdb_arch_exit();
1077 #ifdef CONFIG_MAGIC_SYSRQ
1078                 unregister_sysrq_key('g', &sysrq_dbg_op);
1079 #endif
1080                 if (kgdb_con_registered) {
1081                         unregister_console(&kgdbcons);
1082                         kgdb_con_registered = 0;
1083                 }
1084         }
1085 }
1086
1087 /*
1088  * There are times a tasklet needs to be used vs a compiled in
1089  * break point so as to cause an exception outside a kgdb I/O module,
1090  * such as is the case with kgdboe, where calling a breakpoint in the
1091  * I/O driver itself would be fatal.
1092  */
1093 static void kgdb_tasklet_bpt(unsigned long ing)
1094 {
1095         kgdb_breakpoint();
1096         atomic_set(&kgdb_break_tasklet_var, 0);
1097 }
1098
1099 static DECLARE_TASKLET_OLD(kgdb_tasklet_breakpoint, kgdb_tasklet_bpt);
1100
1101 void kgdb_schedule_breakpoint(void)
1102 {
1103         if (atomic_read(&kgdb_break_tasklet_var) ||
1104                 atomic_read(&kgdb_active) != -1 ||
1105                 atomic_read(&kgdb_setting_breakpoint))
1106                 return;
1107         atomic_inc(&kgdb_break_tasklet_var);
1108         tasklet_schedule(&kgdb_tasklet_breakpoint);
1109 }
1110 EXPORT_SYMBOL_GPL(kgdb_schedule_breakpoint);
1111
1112 /**
1113  *      kgdb_register_io_module - register KGDB IO module
1114  *      @new_dbg_io_ops: the io ops vector
1115  *
1116  *      Register it with the KGDB core.
1117  */
1118 int kgdb_register_io_module(struct kgdb_io *new_dbg_io_ops)
1119 {
1120         struct kgdb_io *old_dbg_io_ops;
1121         int err;
1122
1123         spin_lock(&kgdb_registration_lock);
1124
1125         old_dbg_io_ops = dbg_io_ops;
1126         if (old_dbg_io_ops) {
1127                 if (!old_dbg_io_ops->deinit) {
1128                         spin_unlock(&kgdb_registration_lock);
1129
1130                         pr_err("KGDB I/O driver %s can't replace %s.\n",
1131                                 new_dbg_io_ops->name, old_dbg_io_ops->name);
1132                         return -EBUSY;
1133                 }
1134                 pr_info("Replacing I/O driver %s with %s\n",
1135                         old_dbg_io_ops->name, new_dbg_io_ops->name);
1136         }
1137
1138         if (new_dbg_io_ops->init) {
1139                 err = new_dbg_io_ops->init();
1140                 if (err) {
1141                         spin_unlock(&kgdb_registration_lock);
1142                         return err;
1143                 }
1144         }
1145
1146         dbg_io_ops = new_dbg_io_ops;
1147
1148         spin_unlock(&kgdb_registration_lock);
1149
1150         if (old_dbg_io_ops) {
1151                 old_dbg_io_ops->deinit();
1152                 return 0;
1153         }
1154
1155         pr_info("Registered I/O driver %s\n", new_dbg_io_ops->name);
1156
1157         /* Arm KGDB now. */
1158         kgdb_register_callbacks();
1159
1160         if (kgdb_break_asap &&
1161             (!dbg_is_early || IS_ENABLED(CONFIG_ARCH_HAS_EARLY_DEBUG)))
1162                 kgdb_initial_breakpoint();
1163
1164         return 0;
1165 }
1166 EXPORT_SYMBOL_GPL(kgdb_register_io_module);
1167
1168 /**
1169  *      kkgdb_unregister_io_module - unregister KGDB IO module
1170  *      @old_dbg_io_ops: the io ops vector
1171  *
1172  *      Unregister it with the KGDB core.
1173  */
1174 void kgdb_unregister_io_module(struct kgdb_io *old_dbg_io_ops)
1175 {
1176         BUG_ON(kgdb_connected);
1177
1178         /*
1179          * KGDB is no longer able to communicate out, so
1180          * unregister our callbacks and reset state.
1181          */
1182         kgdb_unregister_callbacks();
1183
1184         spin_lock(&kgdb_registration_lock);
1185
1186         WARN_ON_ONCE(dbg_io_ops != old_dbg_io_ops);
1187         dbg_io_ops = NULL;
1188
1189         spin_unlock(&kgdb_registration_lock);
1190
1191         if (old_dbg_io_ops->deinit)
1192                 old_dbg_io_ops->deinit();
1193
1194         pr_info("Unregistered I/O driver %s, debugger disabled\n",
1195                 old_dbg_io_ops->name);
1196 }
1197 EXPORT_SYMBOL_GPL(kgdb_unregister_io_module);
1198
1199 int dbg_io_get_char(void)
1200 {
1201         int ret = dbg_io_ops->read_char();
1202         if (ret == NO_POLL_CHAR)
1203                 return -1;
1204         if (!dbg_kdb_mode)
1205                 return ret;
1206         if (ret == 127)
1207                 return 8;
1208         return ret;
1209 }
1210
1211 /**
1212  * kgdb_breakpoint - generate breakpoint exception
1213  *
1214  * This function will generate a breakpoint exception.  It is used at the
1215  * beginning of a program to sync up with a debugger and can be used
1216  * otherwise as a quick means to stop program execution and "break" into
1217  * the debugger.
1218  */
1219 noinline void kgdb_breakpoint(void)
1220 {
1221         atomic_inc(&kgdb_setting_breakpoint);
1222         wmb(); /* Sync point before breakpoint */
1223         arch_kgdb_breakpoint();
1224         wmb(); /* Sync point after breakpoint */
1225         atomic_dec(&kgdb_setting_breakpoint);
1226 }
1227 EXPORT_SYMBOL_GPL(kgdb_breakpoint);
1228
1229 static int __init opt_kgdb_wait(char *str)
1230 {
1231         kgdb_break_asap = 1;
1232
1233         kdb_init(KDB_INIT_EARLY);
1234         if (kgdb_io_module_registered &&
1235             IS_ENABLED(CONFIG_ARCH_HAS_EARLY_DEBUG))
1236                 kgdb_initial_breakpoint();
1237
1238         return 0;
1239 }
1240
1241 early_param("kgdbwait", opt_kgdb_wait);