1 files changed, 1239 insertions, 0 deletions

diff --git a/kernel/debug/debug_core.c b/kernel/debug/debug_core.c
new file mode 100644
index 000000000..3a904d869
--- /dev/null
+++ b/kernel/debug/debug_core.c
@@ -0,0 +1,1239 @@
+// 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/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;
+
+	/* 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;
+
+	debug_locks_off();
+	console_flush_on_panic(CONSOLE_FLUSH_PENDING);
+
+	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);