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	Version: linux-6.0.1 spark-3.0.0 hadoop-3.2.0-src hadoop-3.3.0-src spark-2.4.7 linux-4.15.13 hadoop-2.7.4-src Revert   Change

 // SPDX-License-Identifier: GPL-2.0-only
 /*
  * Kernel Debug Core
  *
  * Maintainer: Jason Wessel <jason.wessel@windriver.com>
  *
  * Copyright (C) 2000-2001 VERITAS Software Corporation.
  * Copyright (C) 2002-2004 Timesys Corporation
  * Copyright (C) 2003-2004 Amit S. Kale <amitkale@linsyssoft.com>
  * Copyright (C) 2004 Pavel Machek <pavel@ucw.cz>
  * Copyright (C) 2004-2006 Tom Rini <trini@kernel.crashing.org>
  * Copyright (C) 2004-2006 LinSysSoft Technologies Pvt. Ltd.
  * Copyright (C) 2005-2009 Wind River Systems, Inc.
  * Copyright (C) 2007 MontaVista Software, Inc.
  * Copyright (C) 2008 Red Hat, Inc., Ingo Molnar <mingo@redhat.com>
  *
  * Contributors at various stages not listed above:
  *  Jason Wessel ( jason.wessel@windriver.com )
  *  George Anzinger <george@mvista.com>
  *  Anurekh Saxena (anurekh.saxena@timesys.com)
  *  Lake Stevens Instrument Division (Glenn Engel)
  *  Jim Kingdon, Cygnus Support.
  *
  * Original KGDB stub: David Grothe <dave@gcom.com>,
  * Tigran Aivazian <tigran@sco.com>
  */
 
 #define pr_fmt(fmt) "KGDB: " fmt
 
 #include <linux/pid_namespace.h>
 #include <linux/clocksource.h>
 #include <linux/serial_core.h>
 #include <linux/interrupt.h>
 #include <linux/spinlock.h>
 #include <linux/console.h>
 #include <linux/threads.h>
 #include <linux/uaccess.h>
 #include <linux/kernel.h>
 #include <linux/module.h>
 #include <linux/ptrace.h>
 #include <linux/string.h>
 #include <linux/delay.h>
 #include <linux/sched.h>
 #include <linux/sysrq.h>
 #include <linux/reboot.h>
 #include <linux/init.h>
 #include <linux/kgdb.h>
 #include <linux/kdb.h>
 #include <linux/nmi.h>
 #include <linux/pid.h>
 #include <linux/smp.h>
 #include <linux/mm.h>
 #include <linux/vmacache.h>
 #include <linux/rcupdate.h>
 #include <linux/irq.h>
 #include <linux/security.h>
 
 #include <asm/cacheflush.h>
 #include <asm/byteorder.h>
 #include <linux/atomic.h>
 
 #include "debug_core.h"
 
 static int kgdb_break_asap;
 
 struct debuggerinfo_struct kgdb_info[NR_CPUS];
 
 /* kgdb_connected - Is a host GDB connected to us? */
 int             kgdb_connected;
 EXPORT_SYMBOL_GPL(kgdb_connected);
 
 /* All the KGDB handlers are installed */
 int         kgdb_io_module_registered;
 
 /* Guard for recursive entry */
 static int          exception_level;
 
 struct kgdb_io      *dbg_io_ops;
 static DEFINE_SPINLOCK(kgdb_registration_lock);
 
 /* Action for the reboot notifier, a global allow kdb to change it */
 static int kgdbreboot;
 /* kgdb console driver is loaded */
 static int kgdb_con_registered;
 /* determine if kgdb console output should be used */
 static int kgdb_use_con;
 /* Flag for alternate operations for early debugging */
 bool dbg_is_early = true;
 /* Next cpu to become the master debug core */
 int dbg_switch_cpu;
 
 /* Use kdb or gdbserver mode */
 int dbg_kdb_mode = 1;
 
 module_param(kgdb_use_con, int, 0644);
 module_param(kgdbreboot, int, 0644);
 
 /*
  * Holds information about breakpoints in a kernel. These breakpoints are
  * added and removed by gdb.
  */
 static struct kgdb_bkpt     kgdb_break[KGDB_MAX_BREAKPOINTS] = {
     [0 ... KGDB_MAX_BREAKPOINTS-1] = { .state = BP_UNDEFINED }
 };
 
 /*
  * The CPU# of the active CPU, or -1 if none:
  */
 atomic_t            kgdb_active = ATOMIC_INIT(-1);
 EXPORT_SYMBOL_GPL(kgdb_active);
 static DEFINE_RAW_SPINLOCK(dbg_master_lock);
 static DEFINE_RAW_SPINLOCK(dbg_slave_lock);
 
 /*
  * We use NR_CPUs not PERCPU, in case kgdb is used to debug early
  * bootup code (which might not have percpu set up yet):
  */
 static atomic_t         masters_in_kgdb;
 static atomic_t         slaves_in_kgdb;
 atomic_t            kgdb_setting_breakpoint;
 
 struct task_struct      *kgdb_usethread;
 struct task_struct      *kgdb_contthread;
 
 int             kgdb_single_step;
 static pid_t            kgdb_sstep_pid;
 
 /* to keep track of the CPU which is doing the single stepping*/
 atomic_t            kgdb_cpu_doing_single_step = ATOMIC_INIT(-1);
 
 /*
  * If you are debugging a problem where roundup (the collection of
  * all other CPUs) is a problem [this should be extremely rare],
  * then use the nokgdbroundup option to avoid roundup. In that case
  * the other CPUs might interfere with your debugging context, so
  * use this with care:
  */
 static int kgdb_do_roundup = 1;
 
 static int __init opt_nokgdbroundup(char *str)
 {
     kgdb_do_roundup = 0;
 
     return 0;
 }
 
 early_param("nokgdbroundup", opt_nokgdbroundup);
 
 /*
  * Finally, some KGDB code :-)
  */
 
 /*
  * Weak aliases for breakpoint management,
  * can be overridden by architectures when needed:
  */
 int __weak kgdb_arch_set_breakpoint(struct kgdb_bkpt *bpt)
 {
     int err;
 
     err = copy_from_kernel_nofault(bpt->saved_instr, (char *)bpt->bpt_addr,
                 BREAK_INSTR_SIZE);
     if (err)
         return err;
     err = copy_to_kernel_nofault((char *)bpt->bpt_addr,
                  arch_kgdb_ops.gdb_bpt_instr, BREAK_INSTR_SIZE);
     return err;
 }
 NOKPROBE_SYMBOL(kgdb_arch_set_breakpoint);
 
 int __weak kgdb_arch_remove_breakpoint(struct kgdb_bkpt *bpt)
 {
     return copy_to_kernel_nofault((char *)bpt->bpt_addr,
                   (char *)bpt->saved_instr, BREAK_INSTR_SIZE);
 }
 NOKPROBE_SYMBOL(kgdb_arch_remove_breakpoint);
 
 int __weak kgdb_validate_break_address(unsigned long addr)
 {
     struct kgdb_bkpt tmp;
     int err;
 
     if (kgdb_within_blocklist(addr))
         return -EINVAL;
 
     /* Validate setting the breakpoint and then removing it.  If the
      * remove fails, the kernel needs to emit a bad message because we
      * are deep trouble not being able to put things back the way we
      * found them.
      */
     tmp.bpt_addr = addr;
     err = kgdb_arch_set_breakpoint(&tmp);
     if (err)
         return err;
     err = kgdb_arch_remove_breakpoint(&tmp);
     if (err)
         pr_err("Critical breakpoint error, kernel memory destroyed at: %lx\n",
                addr);
     return err;
 }
 
 unsigned long __weak kgdb_arch_pc(int exception, struct pt_regs *regs)
 {
     return instruction_pointer(regs);
 }
 NOKPROBE_SYMBOL(kgdb_arch_pc);
 
 int __weak kgdb_arch_init(void)
 {
     return 0;
 }
 
 int __weak kgdb_skipexception(int exception, struct pt_regs *regs)
 {
     return 0;
 }
 NOKPROBE_SYMBOL(kgdb_skipexception);
 
 #ifdef CONFIG_SMP
 
 /*
  * Default (weak) implementation for kgdb_roundup_cpus
  */
 
 void __weak kgdb_call_nmi_hook(void *ignored)
 {
     /*
      * NOTE: get_irq_regs() is supposed to get the registers from
      * before the IPI interrupt happened and so is supposed to
      * show where the processor was.  In some situations it's
      * possible we might be called without an IPI, so it might be
      * safer to figure out how to make kgdb_breakpoint() work
      * properly here.
      */
     kgdb_nmicallback(raw_smp_processor_id(), get_irq_regs());
 }
 NOKPROBE_SYMBOL(kgdb_call_nmi_hook);
 
 static DEFINE_PER_CPU(call_single_data_t, kgdb_roundup_csd) =
     CSD_INIT(kgdb_call_nmi_hook, NULL);
 
 void __weak kgdb_roundup_cpus(void)
 {
     call_single_data_t *csd;
     int this_cpu = raw_smp_processor_id();
     int cpu;
     int ret;
 
     for_each_online_cpu(cpu) {
         /* No need to roundup ourselves */
         if (cpu == this_cpu)
             continue;
 
         csd = &per_cpu(kgdb_roundup_csd, cpu);
 
         /*
          * If it didn't round up last time, don't try again
          * since smp_call_function_single_async() will block.
          *
          * If rounding_up is false then we know that the
          * previous call must have at least started and that
          * means smp_call_function_single_async() won't block.
          */
         if (kgdb_info[cpu].rounding_up)
             continue;
         kgdb_info[cpu].rounding_up = true;
 
         ret = smp_call_function_single_async(cpu, csd);
         if (ret)
             kgdb_info[cpu].rounding_up = false;
     }
 }
 NOKPROBE_SYMBOL(kgdb_roundup_cpus);
 
 #endif
 
 /*
  * Some architectures need cache flushes when we set/clear a
  * breakpoint:
  */
 static void kgdb_flush_swbreak_addr(unsigned long addr)
 {
     if (!CACHE_FLUSH_IS_SAFE)
         return;
 
     if (current->mm) {
         int i;
 
         for (i = 0; i < VMACACHE_SIZE; i++) {
             if (!current->vmacache.vmas[i])
                 continue;
             flush_cache_range(current->vmacache.vmas[i],
                       addr, addr + BREAK_INSTR_SIZE);
         }
     }
 
     /* Force flush instruction cache if it was outside the mm */
     flush_icache_range(addr, addr + BREAK_INSTR_SIZE);
 }
 NOKPROBE_SYMBOL(kgdb_flush_swbreak_addr);
 
 /*
  * SW breakpoint management:
  */
 int dbg_activate_sw_breakpoints(void)
 {
     int error;
     int ret = 0;
     int i;
 
     for (i = 0; i < KGDB_MAX_BREAKPOINTS; i++) {
         if (kgdb_break[i].state != BP_SET)
             continue;
 
         error = kgdb_arch_set_breakpoint(&kgdb_break[i]);
         if (error) {
             ret = error;
             pr_info("BP install failed: %lx\n",
                 kgdb_break[i].bpt_addr);
             continue;
         }
 
         kgdb_flush_swbreak_addr(kgdb_break[i].bpt_addr);
         kgdb_break[i].state = BP_ACTIVE;
     }
     return ret;
 }
 NOKPROBE_SYMBOL(dbg_activate_sw_breakpoints);
 
 int dbg_set_sw_break(unsigned long addr)
 {
     int err = kgdb_validate_break_address(addr);
     int breakno = -1;
     int i;
 
     if (err)
         return err;
 
     for (i = 0; i < KGDB_MAX_BREAKPOINTS; i++) {
         if ((kgdb_break[i].state == BP_SET) &&
                     (kgdb_break[i].bpt_addr == addr))
             return -EEXIST;
     }
     for (i = 0; i < KGDB_MAX_BREAKPOINTS; i++) {
         if (kgdb_break[i].state == BP_REMOVED &&
                     kgdb_break[i].bpt_addr == addr) {
             breakno = i;
             break;
         }
     }
 
     if (breakno == -1) {
         for (i = 0; i < KGDB_MAX_BREAKPOINTS; i++) {
             if (kgdb_break[i].state == BP_UNDEFINED) {
                 breakno = i;
                 break;
             }
         }
     }
 
     if (breakno == -1)
         return -E2BIG;
 
     kgdb_break[breakno].state = BP_SET;
     kgdb_break[breakno].type = BP_BREAKPOINT;
     kgdb_break[breakno].bpt_addr = addr;
 
     return 0;
 }
 
 int dbg_deactivate_sw_breakpoints(void)
 {
     int error;
     int ret = 0;
     int i;
 
     for (i = 0; i < KGDB_MAX_BREAKPOINTS; i++) {
         if (kgdb_break[i].state != BP_ACTIVE)
             continue;
         error = kgdb_arch_remove_breakpoint(&kgdb_break[i]);
         if (error) {
             pr_info("BP remove failed: %lx\n",
                 kgdb_break[i].bpt_addr);
             ret = error;
         }
 
         kgdb_flush_swbreak_addr(kgdb_break[i].bpt_addr);
         kgdb_break[i].state = BP_SET;
     }
     return ret;
 }
 NOKPROBE_SYMBOL(dbg_deactivate_sw_breakpoints);
 
 int dbg_remove_sw_break(unsigned long addr)
 {
     int i;
 
     for (i = 0; i < KGDB_MAX_BREAKPOINTS; i++) {
         if ((kgdb_break[i].state == BP_SET) &&
                 (kgdb_break[i].bpt_addr == addr)) {
             kgdb_break[i].state = BP_REMOVED;
             return 0;
         }
     }
     return -ENOENT;
 }
 
 int kgdb_isremovedbreak(unsigned long addr)
 {
     int i;
 
     for (i = 0; i < KGDB_MAX_BREAKPOINTS; i++) {
         if ((kgdb_break[i].state == BP_REMOVED) &&
                     (kgdb_break[i].bpt_addr == addr))
             return 1;
     }
     return 0;
 }
 
 int kgdb_has_hit_break(unsigned long addr)
 {
     int i;
 
     for (i = 0; i < KGDB_MAX_BREAKPOINTS; i++) {
         if (kgdb_break[i].state == BP_ACTIVE &&
             kgdb_break[i].bpt_addr == addr)
             return 1;
     }
     return 0;
 }
 
 int dbg_remove_all_break(void)
 {
     int error;
     int i;
 
     /* Clear memory breakpoints. */
     for (i = 0; i < KGDB_MAX_BREAKPOINTS; i++) {
         if (kgdb_break[i].state != BP_ACTIVE)
             goto setundefined;
         error = kgdb_arch_remove_breakpoint(&kgdb_break[i]);
         if (error)
             pr_err("breakpoint remove failed: %lx\n",
                    kgdb_break[i].bpt_addr);
 setundefined:
         kgdb_break[i].state = BP_UNDEFINED;
     }
 
     /* Clear hardware breakpoints. */
     if (arch_kgdb_ops.remove_all_hw_break)
         arch_kgdb_ops.remove_all_hw_break();
 
     return 0;
 }
 
 void kgdb_free_init_mem(void)
 {
     int i;
 
     /* Clear init memory breakpoints. */
     for (i = 0; i < KGDB_MAX_BREAKPOINTS; i++) {
         if (init_section_contains((void *)kgdb_break[i].bpt_addr, 0))
             kgdb_break[i].state = BP_UNDEFINED;
     }
 }
 
 #ifdef CONFIG_KGDB_KDB
 void kdb_dump_stack_on_cpu(int cpu)
 {
     if (cpu == raw_smp_processor_id() || !IS_ENABLED(CONFIG_SMP)) {
         dump_stack();
         return;
     }
 
     if (!(kgdb_info[cpu].exception_state & DCPU_IS_SLAVE)) {
         kdb_printf("ERROR: Task on cpu %d didn't stop in the debugger\n",
                cpu);
         return;
     }
 
     /*
      * In general, architectures don't support dumping the stack of a
      * "running" process that's not the current one.  From the point of
      * view of the Linux, kernel processes that are looping in the kgdb
      * slave loop are still "running".  There's also no API (that actually
      * works across all architectures) that can do a stack crawl based
      * on registers passed as a parameter.
      *
      * Solve this conundrum by asking slave CPUs to do the backtrace
      * themselves.
      */
     kgdb_info[cpu].exception_state |= DCPU_WANT_BT;
     while (kgdb_info[cpu].exception_state & DCPU_WANT_BT)
         cpu_relax();
 }
 #endif
 
 /*
  * Return true if there is a valid kgdb I/O module.  Also if no
  * debugger is attached a message can be printed to the console about
  * waiting for the debugger to attach.
  *
  * The print_wait argument is only to be true when called from inside
  * the core kgdb_handle_exception, because it will wait for the
  * debugger to attach.
  */
 static int kgdb_io_ready(int print_wait)
 {
     if (!dbg_io_ops)
         return 0;
     if (kgdb_connected)
         return 1;
     if (atomic_read(&kgdb_setting_breakpoint))
         return 1;
     if (print_wait) {
 #ifdef CONFIG_KGDB_KDB
         if (!dbg_kdb_mode)
             pr_crit("waiting... or $3#33 for KDB\n");
 #else
         pr_crit("Waiting for remote debugger\n");
 #endif
     }
     return 1;
 }
 NOKPROBE_SYMBOL(kgdb_io_ready);
 
 static int kgdb_reenter_check(struct kgdb_state *ks)
 {
     unsigned long addr;
 
     if (atomic_read(&kgdb_active) != raw_smp_processor_id())
         return 0;
 
     /* Panic on recursive debugger calls: */
     exception_level++;
     addr = kgdb_arch_pc(ks->ex_vector, ks->linux_regs);
     dbg_deactivate_sw_breakpoints();
 
     /*
      * If the break point removed ok at the place exception
      * occurred, try to recover and print a warning to the end
      * user because the user planted a breakpoint in a place that
      * KGDB needs in order to function.
      */
     if (dbg_remove_sw_break(addr) == 0) {
         exception_level = 0;
         kgdb_skipexception(ks->ex_vector, ks->linux_regs);
         dbg_activate_sw_breakpoints();
         pr_crit("re-enter error: breakpoint removed %lx\n", addr);
         WARN_ON_ONCE(1);
 
         return 1;
     }
     dbg_remove_all_break();
     kgdb_skipexception(ks->ex_vector, ks->linux_regs);
 
     if (exception_level > 1) {
         dump_stack();
         kgdb_io_module_registered = false;
         panic("Recursive entry to debugger");
     }
 
     pr_crit("re-enter exception: ALL breakpoints killed\n");
 #ifdef CONFIG_KGDB_KDB
     /* Allow kdb to debug itself one level */
     return 0;
 #endif
     dump_stack();
     panic("Recursive entry to debugger");
 
     return 1;
 }
 NOKPROBE_SYMBOL(kgdb_reenter_check);
 
 static void dbg_touch_watchdogs(void)
 {
     touch_softlockup_watchdog_sync();
     clocksource_touch_watchdog();
     rcu_cpu_stall_reset();
 }
 NOKPROBE_SYMBOL(dbg_touch_watchdogs);
 
 static int kgdb_cpu_enter(struct kgdb_state *ks, struct pt_regs *regs,
         int exception_state)
 {
     unsigned long flags;
     int sstep_tries = 100;
     int error;
     int cpu;
     int trace_on = 0;
     int online_cpus = num_online_cpus();
     u64 time_left;
 
     kgdb_info[ks->cpu].enter_kgdb++;
     kgdb_info[ks->cpu].exception_state |= exception_state;
 
     if (exception_state == DCPU_WANT_MASTER)
         atomic_inc(&masters_in_kgdb);
     else
         atomic_inc(&slaves_in_kgdb);
 
     if (arch_kgdb_ops.disable_hw_break)
         arch_kgdb_ops.disable_hw_break(regs);
 
 acquirelock:
     rcu_read_lock();
     /*
      * Interrupts will be restored by the 'trap return' code, except when
      * single stepping.
      */
     local_irq_save(flags);
 
     cpu = ks->cpu;
     kgdb_info[cpu].debuggerinfo = regs;
     kgdb_info[cpu].task = current;
     kgdb_info[cpu].ret_state = 0;
     kgdb_info[cpu].irq_depth = hardirq_count() >> HARDIRQ_SHIFT;
 
     /* Make sure the above info reaches the primary CPU */
     smp_mb();
 
     if (exception_level == 1) {
         if (raw_spin_trylock(&dbg_master_lock))
             atomic_xchg(&kgdb_active, cpu);
         goto cpu_master_loop;
     }
 
     /*
      * CPU will loop if it is a slave or request to become a kgdb
      * master cpu and acquire the kgdb_active lock:
      */
     while (1) {
 cpu_loop:
         if (kgdb_info[cpu].exception_state & DCPU_NEXT_MASTER) {
             kgdb_info[cpu].exception_state &= ~DCPU_NEXT_MASTER;
             goto cpu_master_loop;
         } else if (kgdb_info[cpu].exception_state & DCPU_WANT_MASTER) {
             if (raw_spin_trylock(&dbg_master_lock)) {
                 atomic_xchg(&kgdb_active, cpu);
                 break;
             }
         } else if (kgdb_info[cpu].exception_state & DCPU_WANT_BT) {
             dump_stack();
             kgdb_info[cpu].exception_state &= ~DCPU_WANT_BT;
         } else if (kgdb_info[cpu].exception_state & DCPU_IS_SLAVE) {
             if (!raw_spin_is_locked(&dbg_slave_lock))
                 goto return_normal;
         } else {
 return_normal:
             /* Return to normal operation by executing any
              * hw breakpoint fixup.
              */
             if (arch_kgdb_ops.correct_hw_break)
                 arch_kgdb_ops.correct_hw_break();
             if (trace_on)
                 tracing_on();
             kgdb_info[cpu].debuggerinfo = NULL;
             kgdb_info[cpu].task = NULL;
             kgdb_info[cpu].exception_state &=
                 ~(DCPU_WANT_MASTER | DCPU_IS_SLAVE);
             kgdb_info[cpu].enter_kgdb--;
             smp_mb__before_atomic();
             atomic_dec(&slaves_in_kgdb);
             dbg_touch_watchdogs();
             local_irq_restore(flags);
             rcu_read_unlock();
             return 0;
         }
         cpu_relax();
     }
 
     /*
      * For single stepping, try to only enter on the processor
      * that was single stepping.  To guard against a deadlock, the
      * kernel will only try for the value of sstep_tries before
      * giving up and continuing on.
      */
     if (atomic_read(&kgdb_cpu_doing_single_step) != -1 &&
         (kgdb_info[cpu].task &&
          kgdb_info[cpu].task->pid != kgdb_sstep_pid) && --sstep_tries) {
         atomic_set(&kgdb_active, -1);
         raw_spin_unlock(&dbg_master_lock);
         dbg_touch_watchdogs();
         local_irq_restore(flags);
         rcu_read_unlock();
 
         goto acquirelock;
     }
 
     if (!kgdb_io_ready(1)) {
         kgdb_info[cpu].ret_state = 1;
         goto kgdb_restore; /* No I/O connection, resume the system */
     }
 
     /*
      * Don't enter if we have hit a removed breakpoint.
      */
     if (kgdb_skipexception(ks->ex_vector, ks->linux_regs))
         goto kgdb_restore;
 
     atomic_inc(&ignore_console_lock_warning);
 
     /* Call the I/O driver's pre_exception routine */
     if (dbg_io_ops->pre_exception)
         dbg_io_ops->pre_exception();
 
     /*
      * Get the passive CPU lock which will hold all the non-primary
      * CPU in a spin state while the debugger is active
      */
     if (!kgdb_single_step)
         raw_spin_lock(&dbg_slave_lock);
 
 #ifdef CONFIG_SMP
     /* If send_ready set, slaves are already waiting */
     if (ks->send_ready)
         atomic_set(ks->send_ready, 1);
 
     /* Signal the other CPUs to enter kgdb_wait() */
     else if ((!kgdb_single_step) && kgdb_do_roundup)
         kgdb_roundup_cpus();
 #endif
 
     /*
      * Wait for the other CPUs to be notified and be waiting for us:
      */
     time_left = MSEC_PER_SEC;
     while (kgdb_do_roundup && --time_left &&
            (atomic_read(&masters_in_kgdb) + atomic_read(&slaves_in_kgdb)) !=
            online_cpus)
         udelay(1000);
     if (!time_left)
         pr_crit("Timed out waiting for secondary CPUs.\n");
 
     /*
      * At this point the primary processor is completely
      * in the debugger and all secondary CPUs are quiescent
      */
     dbg_deactivate_sw_breakpoints();
     kgdb_single_step = 0;
     kgdb_contthread = current;
     exception_level = 0;
     trace_on = tracing_is_on();
     if (trace_on)
         tracing_off();
 
     while (1) {
 cpu_master_loop:
         if (dbg_kdb_mode) {
             kgdb_connected = 1;
             error = kdb_stub(ks);
             if (error == -1)
                 continue;
             kgdb_connected = 0;
         } else {
             /*
              * This is a brutal way to interfere with the debugger
              * and prevent gdb being used to poke at kernel memory.
              * This could cause trouble if lockdown is applied when
              * there is already an active gdb session. For now the
              * answer is simply "don't do that". Typically lockdown
              * *will* be applied before the debug core gets started
              * so only developers using kgdb for fairly advanced
              * early kernel debug can be biten by this. Hopefully
              * they are sophisticated enough to take care of
              * themselves, especially with help from the lockdown
              * message printed on the console!
              */
             if (security_locked_down(LOCKDOWN_DBG_WRITE_KERNEL)) {
                 if (IS_ENABLED(CONFIG_KGDB_KDB)) {
                     /* Switch back to kdb if possible... */
                     dbg_kdb_mode = 1;
                     continue;
                 } else {
                     /* ... otherwise just bail */
                     break;
                 }
             }
             error = gdb_serial_stub(ks);
         }
 
         if (error == DBG_PASS_EVENT) {
             dbg_kdb_mode = !dbg_kdb_mode;
         } else if (error == DBG_SWITCH_CPU_EVENT) {
             kgdb_info[dbg_switch_cpu].exception_state |=
                 DCPU_NEXT_MASTER;
             goto cpu_loop;
         } else {
             kgdb_info[cpu].ret_state = error;
             break;
         }
     }
 
     dbg_activate_sw_breakpoints();
 
     /* Call the I/O driver's post_exception routine */
     if (dbg_io_ops->post_exception)
         dbg_io_ops->post_exception();
 
     atomic_dec(&ignore_console_lock_warning);
 
     if (!kgdb_single_step) {
         raw_spin_unlock(&dbg_slave_lock);
         /* Wait till all the CPUs have quit from the debugger. */
         while (kgdb_do_roundup && atomic_read(&slaves_in_kgdb))
             cpu_relax();
     }
 
 kgdb_restore:
     if (atomic_read(&kgdb_cpu_doing_single_step) != -1) {
         int sstep_cpu = atomic_read(&kgdb_cpu_doing_single_step);
         if (kgdb_info[sstep_cpu].task)
             kgdb_sstep_pid = kgdb_info[sstep_cpu].task->pid;
         else
             kgdb_sstep_pid = 0;
     }
     if (arch_kgdb_ops.correct_hw_break)
         arch_kgdb_ops.correct_hw_break();
     if (trace_on)
         tracing_on();
 
     kgdb_info[cpu].debuggerinfo = NULL;
     kgdb_info[cpu].task = NULL;
     kgdb_info[cpu].exception_state &=
         ~(DCPU_WANT_MASTER | DCPU_IS_SLAVE);
     kgdb_info[cpu].enter_kgdb--;
     smp_mb__before_atomic();
     atomic_dec(&masters_in_kgdb);
     /* Free kgdb_active */
     atomic_set(&kgdb_active, -1);
     raw_spin_unlock(&dbg_master_lock);
     dbg_touch_watchdogs();
     local_irq_restore(flags);
     rcu_read_unlock();
 
     return kgdb_info[cpu].ret_state;
 }
 NOKPROBE_SYMBOL(kgdb_cpu_enter);
 
 /*
  * kgdb_handle_exception() - main entry point from a kernel exception
  *
  * Locking hierarchy:
  *  interface locks, if any (begin_session)
  *  kgdb lock (kgdb_active)
  */
 int
 kgdb_handle_exception(int evector, int signo, int ecode, struct pt_regs *regs)
 {
     struct kgdb_state kgdb_var;
     struct kgdb_state *ks = &kgdb_var;
     int ret = 0;
 
     if (arch_kgdb_ops.enable_nmi)
         arch_kgdb_ops.enable_nmi(0);
     /*
      * Avoid entering the debugger if we were triggered due to an oops
      * but panic_timeout indicates the system should automatically
      * reboot on panic. We don't want to get stuck waiting for input
      * on such systems, especially if its "just" an oops.
      */
     if (signo != SIGTRAP && panic_timeout)
         return 1;
 
     memset(ks, 0, sizeof(struct kgdb_state));
     ks->cpu         = raw_smp_processor_id();
     ks->ex_vector       = evector;
     ks->signo       = signo;
     ks->err_code        = ecode;
     ks->linux_regs      = regs;
 
     if (kgdb_reenter_check(ks))
         goto out; /* Ouch, double exception ! */
     if (kgdb_info[ks->cpu].enter_kgdb != 0)
         goto out;
 
     ret = kgdb_cpu_enter(ks, regs, DCPU_WANT_MASTER);
 out:
     if (arch_kgdb_ops.enable_nmi)
         arch_kgdb_ops.enable_nmi(1);
     return ret;
 }
 NOKPROBE_SYMBOL(kgdb_handle_exception);
 
 /*
  * GDB places a breakpoint at this function to know dynamically loaded objects.
  */
 static int module_event(struct notifier_block *self, unsigned long val,
     void *data)
 {
     return 0;
 }
 
 static struct notifier_block dbg_module_load_nb = {
     .notifier_call  = module_event,
 };
 
 int kgdb_nmicallback(int cpu, void *regs)
 {
 #ifdef CONFIG_SMP
     struct kgdb_state kgdb_var;
     struct kgdb_state *ks = &kgdb_var;
 
     kgdb_info[cpu].rounding_up = false;
 
     memset(ks, 0, sizeof(struct kgdb_state));
     ks->cpu         = cpu;
     ks->linux_regs      = regs;
 
     if (kgdb_info[ks->cpu].enter_kgdb == 0 &&
             raw_spin_is_locked(&dbg_master_lock)) {
         kgdb_cpu_enter(ks, regs, DCPU_IS_SLAVE);
         return 0;
     }
 #endif
     return 1;
 }
 NOKPROBE_SYMBOL(kgdb_nmicallback);
 
 int kgdb_nmicallin(int cpu, int trapnr, void *regs, int err_code,
                             atomic_t *send_ready)
 {
 #ifdef CONFIG_SMP
     if (!kgdb_io_ready(0) || !send_ready)
         return 1;
 
     if (kgdb_info[cpu].enter_kgdb == 0) {
         struct kgdb_state kgdb_var;
         struct kgdb_state *ks = &kgdb_var;
 
         memset(ks, 0, sizeof(struct kgdb_state));
         ks->cpu         = cpu;
         ks->ex_vector       = trapnr;
         ks->signo       = SIGTRAP;
         ks->err_code        = err_code;
         ks->linux_regs      = regs;
         ks->send_ready      = send_ready;
         kgdb_cpu_enter(ks, regs, DCPU_WANT_MASTER);
         return 0;
     }
 #endif
     return 1;
 }
 NOKPROBE_SYMBOL(kgdb_nmicallin);
 
 static void kgdb_console_write(struct console *co, const char *s,
    unsigned count)
 {
     unsigned long flags;
 
     /* If we're debugging, or KGDB has not connected, don't try
      * and print. */
     if (!kgdb_connected || atomic_read(&kgdb_active) != -1 || dbg_kdb_mode)
         return;
 
     local_irq_save(flags);
     gdbstub_msg_write(s, count);
     local_irq_restore(flags);
 }
 
 static struct console kgdbcons = {
     .name       = "kgdb",
     .write      = kgdb_console_write,
     .flags      = CON_PRINTBUFFER | CON_ENABLED,
     .index      = -1,
 };
 
 static int __init opt_kgdb_con(char *str)
 {
     kgdb_use_con = 1;
 
     if (kgdb_io_module_registered && !kgdb_con_registered) {
         register_console(&kgdbcons);
         kgdb_con_registered = 1;
     }
 
     return 0;
 }
 
 early_param("kgdbcon", opt_kgdb_con);
 
 #ifdef CONFIG_MAGIC_SYSRQ
 static void sysrq_handle_dbg(int key)
 {
     if (!dbg_io_ops) {
         pr_crit("ERROR: No KGDB I/O module available\n");
         return;
     }
     if (!kgdb_connected) {
 #ifdef CONFIG_KGDB_KDB
         if (!dbg_kdb_mode)
             pr_crit("KGDB or $3#33 for KDB\n");
 #else
         pr_crit("Entering KGDB\n");
 #endif
     }
 
     kgdb_breakpoint();
 }
 
 static const struct sysrq_key_op sysrq_dbg_op = {
     .handler    = sysrq_handle_dbg,
     .help_msg   = "debug(g)",
     .action_msg = "DEBUG",
 };
 #endif
 
 void kgdb_panic(const char *msg)
 {
     if (!kgdb_io_module_registered)
         return;
 
     /*
      * We don't want to get stuck waiting for input from user if
      * "panic_timeout" indicates the system should automatically
      * reboot on panic.
      */
     if (panic_timeout)
         return;
 
     if (dbg_kdb_mode)
         kdb_printf("PANIC: %s\n", msg);
 
     kgdb_breakpoint();
 }
 
 static void kgdb_initial_breakpoint(void)
 {
     kgdb_break_asap = 0;
 
     pr_crit("Waiting for connection from remote gdb...\n");
     kgdb_breakpoint();
 }
 
 void __weak kgdb_arch_late(void)
 {
 }
 
 void __init dbg_late_init(void)
 {
     dbg_is_early = false;
     if (kgdb_io_module_registered)
         kgdb_arch_late();
     kdb_init(KDB_INIT_FULL);
 
     if (kgdb_io_module_registered && kgdb_break_asap)
         kgdb_initial_breakpoint();
 }
 
 static int
 dbg_notify_reboot(struct notifier_block *this, unsigned long code, void *x)
 {
     /*
      * Take the following action on reboot notify depending on value:
      *    1 == Enter debugger
      *    0 == [the default] detach debug client
      *   -1 == Do nothing... and use this until the board resets
      */
     switch (kgdbreboot) {
     case 1:
         kgdb_breakpoint();
         goto done;
     case -1:
         goto done;
     }
     if (!dbg_kdb_mode)
         gdbstub_exit(code);
 done:
     return NOTIFY_DONE;
 }
 
 static struct notifier_block dbg_reboot_notifier = {
     .notifier_call      = dbg_notify_reboot,
     .next           = NULL,
     .priority       = INT_MAX,
 };
 
 static void kgdb_register_callbacks(void)
 {
     if (!kgdb_io_module_registered) {
         kgdb_io_module_registered = 1;
         kgdb_arch_init();
         if (!dbg_is_early)
             kgdb_arch_late();
         register_module_notifier(&dbg_module_load_nb);
         register_reboot_notifier(&dbg_reboot_notifier);
 #ifdef CONFIG_MAGIC_SYSRQ
         register_sysrq_key('g', &sysrq_dbg_op);
 #endif
         if (kgdb_use_con && !kgdb_con_registered) {
             register_console(&kgdbcons);
             kgdb_con_registered = 1;
         }
     }
 }
 
 static void kgdb_unregister_callbacks(void)
 {
     /*
      * When this routine is called KGDB should unregister from
      * handlers and clean up, making sure it is not handling any
      * break exceptions at the time.
      */
     if (kgdb_io_module_registered) {
         kgdb_io_module_registered = 0;
         unregister_reboot_notifier(&dbg_reboot_notifier);
         unregister_module_notifier(&dbg_module_load_nb);
         kgdb_arch_exit();
 #ifdef CONFIG_MAGIC_SYSRQ
         unregister_sysrq_key('g', &sysrq_dbg_op);
 #endif
         if (kgdb_con_registered) {
             unregister_console(&kgdbcons);
             kgdb_con_registered = 0;
         }
     }
 }
 
 /**
  *  kgdb_register_io_module - register KGDB IO module
  *  @new_dbg_io_ops: the io ops vector
  *
  *  Register it with the KGDB core.
  */
 int kgdb_register_io_module(struct kgdb_io *new_dbg_io_ops)
 {
     struct kgdb_io *old_dbg_io_ops;
     int err;
 
     spin_lock(&kgdb_registration_lock);
 
     old_dbg_io_ops = dbg_io_ops;
     if (old_dbg_io_ops) {
         if (!old_dbg_io_ops->deinit) {
             spin_unlock(&kgdb_registration_lock);
 
             pr_err("KGDB I/O driver %s can't replace %s.\n",
                 new_dbg_io_ops->name, old_dbg_io_ops->name);
             return -EBUSY;
         }
         pr_info("Replacing I/O driver %s with %s\n",
             old_dbg_io_ops->name, new_dbg_io_ops->name);
     }
 
     if (new_dbg_io_ops->init) {
         err = new_dbg_io_ops->init();
         if (err) {
             spin_unlock(&kgdb_registration_lock);
             return err;
         }
     }
 
     dbg_io_ops = new_dbg_io_ops;
 
     spin_unlock(&kgdb_registration_lock);
 
     if (old_dbg_io_ops) {
         old_dbg_io_ops->deinit();
         return 0;
     }
 
     pr_info("Registered I/O driver %s\n", new_dbg_io_ops->name);
 
     /* Arm KGDB now. */
     kgdb_register_callbacks();
 
     if (kgdb_break_asap &&
         (!dbg_is_early || IS_ENABLED(CONFIG_ARCH_HAS_EARLY_DEBUG)))
         kgdb_initial_breakpoint();
 
     return 0;
 }
 EXPORT_SYMBOL_GPL(kgdb_register_io_module);
 
 /**
  *  kgdb_unregister_io_module - unregister KGDB IO module
  *  @old_dbg_io_ops: the io ops vector
  *
  *  Unregister it with the KGDB core.
  */
 void kgdb_unregister_io_module(struct kgdb_io *old_dbg_io_ops)
 {
     BUG_ON(kgdb_connected);
 
     /*
      * KGDB is no longer able to communicate out, so
      * unregister our callbacks and reset state.
      */
     kgdb_unregister_callbacks();
 
     spin_lock(&kgdb_registration_lock);
 
     WARN_ON_ONCE(dbg_io_ops != old_dbg_io_ops);
     dbg_io_ops = NULL;
 
     spin_unlock(&kgdb_registration_lock);
 
     if (old_dbg_io_ops->deinit)
         old_dbg_io_ops->deinit();
 
     pr_info("Unregistered I/O driver %s, debugger disabled\n",
         old_dbg_io_ops->name);
 }
 EXPORT_SYMBOL_GPL(kgdb_unregister_io_module);
 
 int dbg_io_get_char(void)
 {
     int ret = dbg_io_ops->read_char();
     if (ret == NO_POLL_CHAR)
         return -1;
     if (!dbg_kdb_mode)
         return ret;
     if (ret == 127)
         return 8;
     return ret;
 }
 
 /**
  * kgdb_breakpoint - generate breakpoint exception
  *
  * This function will generate a breakpoint exception.  It is used at the
  * beginning of a program to sync up with a debugger and can be used
  * otherwise as a quick means to stop program execution and "break" into
  * the debugger.
  */
 noinline void kgdb_breakpoint(void)
 {
     atomic_inc(&kgdb_setting_breakpoint);
     wmb(); /* Sync point before breakpoint */
     arch_kgdb_breakpoint();
     wmb(); /* Sync point after breakpoint */
     atomic_dec(&kgdb_setting_breakpoint);
 }
 EXPORT_SYMBOL_GPL(kgdb_breakpoint);
 
 static int __init opt_kgdb_wait(char *str)
 {
     kgdb_break_asap = 1;
 
     kdb_init(KDB_INIT_EARLY);
     if (kgdb_io_module_registered &&
         IS_ENABLED(CONFIG_ARCH_HAS_EARLY_DEBUG))
         kgdb_initial_breakpoint();
 
     return 0;
 }
 
 early_param("kgdbwait", opt_kgdb_wait);

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