Merge tag 'kgdb-4.21-rc1' of git://git.kernel.org/pub/scm/linux/kernel/git/danielt/linux

Pull kgdb updates from Daniel Thompson:
 "Mostly clean ups although while Doug's was chasing down a odd lockdep
  warning he also did some work to improved debugger resilience when
  some CPUs fail to respond to the round up request.

  The main changes are:

   - Fixing a lockdep warning on architectures that cannot use an NMI
     for the round up plus related changes to make CPU round up and all
     CPU backtrace more resilient.

   - Constify the arch ops tables

   - A couple of other small clean ups

  Two of the three patchsets here include changes that spill over into
  arch/. Changes in the arch space are relatively narrow in scope (and
  directly related to kgdb). Didn't get comprehensive acks but all
  impacted maintainers were Cc:ed in good time"

* tag 'kgdb-4.21-rc1' of git://git.kernel.org/pub/scm/linux/kernel/git/danielt/linux:
  kgdb/treewide: constify struct kgdb_arch arch_kgdb_ops
  mips/kgdb: prepare arch_kgdb_ops for constness
  kdb: use bool for binary state indicators
  kdb: Don't back trace on a cpu that didn't round up
  kgdb: Don't round up a CPU that failed rounding up before
  kgdb: Fix kgdb_roundup_cpus() for arches who used smp_call_function()
  kgdb: Remove irq flags from roundup

20 files changed, 125 insertions, 141 deletions

diff --git a/arch/arc/kernel/kgdb.c b/arch/arc/kernel/kgdb.c
index 9a3c34af2ae8..96bca9963c63 100644
--- a/arch/arc/kernel/kgdb.c
+++ b/arch/arc/kernel/kgdb.c
@@ -192,19 +192,13 @@ void kgdb_arch_set_pc(struct pt_regs *regs, unsigned long ip)
 	instruction_pointer(regs) = ip;
 }
 
-static void kgdb_call_nmi_hook(void *ignored)
+void kgdb_call_nmi_hook(void *ignored)
 {
+	/* Default implementation passes get_irq_regs() but we don't */
 	kgdb_nmicallback(raw_smp_processor_id(), NULL);
 }
 
-void kgdb_roundup_cpus(unsigned long flags)
-{
-	local_irq_enable();
-	smp_call_function(kgdb_call_nmi_hook, NULL, 0);
-	local_irq_disable();
-}
-
-struct kgdb_arch arch_kgdb_ops = {
+const struct kgdb_arch arch_kgdb_ops = {
 	/* breakpoint instruction: TRAP_S 0x3 */
 #ifdef CONFIG_CPU_BIG_ENDIAN
 	.gdb_bpt_instr		= {0x78, 0x7e},
diff --git a/arch/arm/kernel/kgdb.c b/arch/arm/kernel/kgdb.c
index caa0dbe3dc61..6a95b9296640 100644
--- a/arch/arm/kernel/kgdb.c
+++ b/arch/arm/kernel/kgdb.c
@@ -170,18 +170,6 @@ static struct undef_hook kgdb_compiled_brkpt_hook = {
 	.fn			= kgdb_compiled_brk_fn
 };
 
-static void kgdb_call_nmi_hook(void *ignored)
-{
-       kgdb_nmicallback(raw_smp_processor_id(), get_irq_regs());
-}
-
-void kgdb_roundup_cpus(unsigned long flags)
-{
-       local_irq_enable();
-       smp_call_function(kgdb_call_nmi_hook, NULL, 0);
-       local_irq_disable();
-}
-
 static int __kgdb_notify(struct die_args *args, unsigned long cmd)
 {
 	struct pt_regs *regs = args->regs;
@@ -274,7 +262,7 @@ int kgdb_arch_remove_breakpoint(struct kgdb_bkpt *bpt)
  * and we handle the normal undef case within the do_undefinstr
  * handler.
  */
-struct kgdb_arch arch_kgdb_ops = {
+const struct kgdb_arch arch_kgdb_ops = {
 #ifndef __ARMEB__
 	.gdb_bpt_instr		= {0xfe, 0xde, 0xff, 0xe7}
 #else /* ! __ARMEB__ */
diff --git a/arch/arm64/kernel/kgdb.c b/arch/arm64/kernel/kgdb.c
index a20de58061a8..ce46c4cdf368 100644
--- a/arch/arm64/kernel/kgdb.c
+++ b/arch/arm64/kernel/kgdb.c
@@ -284,18 +284,6 @@ static struct step_hook kgdb_step_hook = {
 	.fn		= kgdb_step_brk_fn
 };
 
-static void kgdb_call_nmi_hook(void *ignored)
-{
-	kgdb_nmicallback(raw_smp_processor_id(), get_irq_regs());
-}
-
-void kgdb_roundup_cpus(unsigned long flags)
-{
-	local_irq_enable();
-	smp_call_function(kgdb_call_nmi_hook, NULL, 0);
-	local_irq_disable();
-}
-
 static int __kgdb_notify(struct die_args *args, unsigned long cmd)
 {
 	struct pt_regs *regs = args->regs;
@@ -357,7 +345,7 @@ void kgdb_arch_exit(void)
 	unregister_die_notifier(&kgdb_notifier);
 }
 
-struct kgdb_arch arch_kgdb_ops;
+const struct kgdb_arch arch_kgdb_ops;
 
 int kgdb_arch_set_breakpoint(struct kgdb_bkpt *bpt)
 {
diff --git a/arch/h8300/kernel/kgdb.c b/arch/h8300/kernel/kgdb.c
index 1a1d30cb0609..602e478afbd5 100644
--- a/arch/h8300/kernel/kgdb.c
+++ b/arch/h8300/kernel/kgdb.c
@@ -129,7 +129,7 @@ void kgdb_arch_exit(void)
 	/* Nothing to do */
 }
 
-struct kgdb_arch arch_kgdb_ops = {
+const struct kgdb_arch arch_kgdb_ops = {
 	/* Breakpoint instruction: trapa #2 */
 	.gdb_bpt_instr = { 0x57, 0x20 },
 };
diff --git a/arch/hexagon/kernel/kgdb.c b/arch/hexagon/kernel/kgdb.c
index 16c24b22d0b2..3fabd3ff3bbd 100644
--- a/arch/hexagon/kernel/kgdb.c
+++ b/arch/hexagon/kernel/kgdb.c
@@ -83,7 +83,7 @@ struct dbg_reg_def_t dbg_reg_def[DBG_MAX_REG_NUM] = {
 	{ "syscall_nr", GDB_SIZEOF_REG, offsetof(struct pt_regs, syscall_nr)},
 };
 
-struct kgdb_arch arch_kgdb_ops = {
+const struct kgdb_arch arch_kgdb_ops = {
 	/* trap0(#0xDB) 0x0cdb0054 */
 	.gdb_bpt_instr = {0x54, 0x00, 0xdb, 0x0c},
 };
@@ -115,38 +115,6 @@ void kgdb_arch_set_pc(struct pt_regs *regs, unsigned long pc)
 	instruction_pointer(regs) = pc;
 }
 
-#ifdef CONFIG_SMP
-
-/**
- * kgdb_roundup_cpus - Get other CPUs into a holding pattern
- * @flags: Current IRQ state
- *
- * On SMP systems, we need to get the attention of the other CPUs
- * and get them be in a known state.  This should do what is needed
- * to get the other CPUs to call kgdb_wait(). Note that on some arches,
- * the NMI approach is not used for rounding up all the CPUs. For example,
- * in case of MIPS, smp_call_function() is used to roundup CPUs. In
- * this case, we have to make sure that interrupts are enabled before
- * calling smp_call_function(). The argument to this function is
- * the flags that will be used when restoring the interrupts. There is
- * local_irq_save() call before kgdb_roundup_cpus().
- *
- * On non-SMP systems, this is not called.
- */
-
-static void hexagon_kgdb_nmi_hook(void *ignored)
-{
-	kgdb_nmicallback(raw_smp_processor_id(), get_irq_regs());
-}
-
-void kgdb_roundup_cpus(unsigned long flags)
-{
-	local_irq_enable();
-	smp_call_function(hexagon_kgdb_nmi_hook, NULL, 0);
-	local_irq_disable();
-}
-#endif
-
 
 /*  Not yet working  */
 void sleeping_thread_to_gdb_regs(unsigned long *gdb_regs,
diff --git a/arch/microblaze/kernel/kgdb.c b/arch/microblaze/kernel/kgdb.c
index 6366f69d118e..130cd0f064ce 100644
--- a/arch/microblaze/kernel/kgdb.c
+++ b/arch/microblaze/kernel/kgdb.c
@@ -143,7 +143,7 @@ void kgdb_arch_exit(void)
 /*
  * Global data
  */
-struct kgdb_arch arch_kgdb_ops = {
+const struct kgdb_arch arch_kgdb_ops = {
 #ifdef __MICROBLAZEEL__
 	.gdb_bpt_instr = {0x18, 0x00, 0x0c, 0xba}, /* brki r16, 0x18 */
 #else
diff --git a/arch/mips/kernel/kgdb.c b/arch/mips/kernel/kgdb.c
index eb6c0d582626..149100e1bc7c 100644
--- a/arch/mips/kernel/kgdb.c
+++ b/arch/mips/kernel/kgdb.c
@@ -207,7 +207,7 @@ void arch_kgdb_breakpoint(void)
 		".set\treorder");
 }
 
-static void kgdb_call_nmi_hook(void *ignored)
+void kgdb_call_nmi_hook(void *ignored)
 {
 	mm_segment_t old_fs;
 
@@ -219,13 +219,6 @@ static void kgdb_call_nmi_hook(void *ignored)
 	set_fs(old_fs);
 }
 
-void kgdb_roundup_cpus(unsigned long flags)
-{
-	local_irq_enable();
-	smp_call_function(kgdb_call_nmi_hook, NULL, 0);
-	local_irq_disable();
-}
-
 static int compute_signal(int tt)
 {
 	struct hard_trap_info *ht;
@@ -394,18 +387,16 @@ int kgdb_arch_handle_exception(int vector, int signo, int err_code,
 	return -1;
 }
 
-struct kgdb_arch arch_kgdb_ops;
+const struct kgdb_arch arch_kgdb_ops = {
+#ifdef CONFIG_CPU_BIG_ENDIAN
+	.gdb_bpt_instr = { spec_op << 2, 0x00, 0x00, break_op },
+#else
+	.gdb_bpt_instr = { break_op, 0x00, 0x00, spec_op << 2 },
+#endif
+};
 
 int kgdb_arch_init(void)
 {
-	union mips_instruction insn = {
-		.r_format = {
-			.opcode = spec_op,
-			.func	= break_op,
-		}
-	};
-	memcpy(arch_kgdb_ops.gdb_bpt_instr, insn.byte, BREAK_INSTR_SIZE);
-
 	register_die_notifier(&kgdb_notifier);
 
 	return 0;
diff --git a/arch/nios2/kernel/kgdb.c b/arch/nios2/kernel/kgdb.c
index 117859122d1c..37b25f844a2d 100644
--- a/arch/nios2/kernel/kgdb.c
+++ b/arch/nios2/kernel/kgdb.c
@@ -165,7 +165,7 @@ void kgdb_arch_exit(void)
 	/* Nothing to do */
 }
 
-struct kgdb_arch arch_kgdb_ops = {
+const struct kgdb_arch arch_kgdb_ops = {
 	/* Breakpoint instruction: trap 30 */
 	.gdb_bpt_instr = { 0xba, 0x6f, 0x3b, 0x00 },
 };
diff --git a/arch/powerpc/kernel/kgdb.c b/arch/powerpc/kernel/kgdb.c
index 59c578f865aa..e1865565f0ae 100644
--- a/arch/powerpc/kernel/kgdb.c
+++ b/arch/powerpc/kernel/kgdb.c
@@ -117,14 +117,14 @@ int kgdb_skipexception(int exception, struct pt_regs *regs)
 	return kgdb_isremovedbreak(regs->nip);
 }
 
-static int kgdb_call_nmi_hook(struct pt_regs *regs)
+static int kgdb_debugger_ipi(struct pt_regs *regs)
 {
 	kgdb_nmicallback(raw_smp_processor_id(), regs);
 	return 0;
 }
 
 #ifdef CONFIG_SMP
-void kgdb_roundup_cpus(unsigned long flags)
+void kgdb_roundup_cpus(void)
 {
 	smp_send_debugger_break();
 }
@@ -477,7 +477,7 @@ int kgdb_arch_remove_breakpoint(struct kgdb_bkpt *bpt)
 /*
  * Global data
  */
-struct kgdb_arch arch_kgdb_ops;
+const struct kgdb_arch arch_kgdb_ops;
 
 static int kgdb_not_implemented(struct pt_regs *regs)
 {
@@ -502,7 +502,7 @@ int kgdb_arch_init(void)
 	old__debugger_break_match = __debugger_break_match;
 	old__debugger_fault_handler = __debugger_fault_handler;
 
-	__debugger_ipi = kgdb_call_nmi_hook;
+	__debugger_ipi = kgdb_debugger_ipi;
 	__debugger = kgdb_debugger;
 	__debugger_bpt = kgdb_handle_breakpoint;
 	__debugger_sstep = kgdb_singlestep;
diff --git a/arch/sh/kernel/kgdb.c b/arch/sh/kernel/kgdb.c
index d24bd2d2ffad..6d61f8cf4c13 100644
--- a/arch/sh/kernel/kgdb.c
+++ b/arch/sh/kernel/kgdb.c
@@ -311,18 +311,6 @@ BUILD_TRAP_HANDLER(singlestep)
 	local_irq_restore(flags);
 }
 
-static void kgdb_call_nmi_hook(void *ignored)
-{
-	kgdb_nmicallback(raw_smp_processor_id(), get_irq_regs());
-}
-
-void kgdb_roundup_cpus(unsigned long flags)
-{
-	local_irq_enable();
-	smp_call_function(kgdb_call_nmi_hook, NULL, 0);
-	local_irq_disable();
-}
-
 static int __kgdb_notify(struct die_args *args, unsigned long cmd)
 {
 	int ret;
@@ -379,7 +367,7 @@ void kgdb_arch_exit(void)
 	unregister_die_notifier(&kgdb_notifier);
 }
 
-struct kgdb_arch arch_kgdb_ops = {
+const struct kgdb_arch arch_kgdb_ops = {
 	/* Breakpoint instruction: trapa #0x3c */
 #ifdef CONFIG_CPU_LITTLE_ENDIAN
 	.gdb_bpt_instr		= { 0x3c, 0xc3 },
diff --git a/arch/sparc/kernel/kgdb_32.c b/arch/sparc/kernel/kgdb_32.c
index 639c8e54530a..7580775a14b9 100644
--- a/arch/sparc/kernel/kgdb_32.c
+++ b/arch/sparc/kernel/kgdb_32.c
@@ -166,7 +166,7 @@ void kgdb_arch_set_pc(struct pt_regs *regs, unsigned long ip)
 	regs->npc = regs->pc + 4;
 }
 
-struct kgdb_arch arch_kgdb_ops = {
+const struct kgdb_arch arch_kgdb_ops = {
 	/* Breakpoint instruction: ta 0x7d */
 	.gdb_bpt_instr		= { 0x91, 0xd0, 0x20, 0x7d },
 };
diff --git a/arch/sparc/kernel/kgdb_64.c b/arch/sparc/kernel/kgdb_64.c
index a68bbddbdba4..5d6c2d287e85 100644
--- a/arch/sparc/kernel/kgdb_64.c
+++ b/arch/sparc/kernel/kgdb_64.c
@@ -195,7 +195,7 @@ void kgdb_arch_set_pc(struct pt_regs *regs, unsigned long ip)
 	regs->tnpc = regs->tpc + 4;
 }
 
-struct kgdb_arch arch_kgdb_ops = {
+const struct kgdb_arch arch_kgdb_ops = {
 	/* Breakpoint instruction: ta 0x72 */
 	.gdb_bpt_instr		= { 0x91, 0xd0, 0x20, 0x72 },
 };
diff --git a/arch/sparc/kernel/smp_64.c b/arch/sparc/kernel/smp_64.c
index 4792e08ad36b..f45d876983f1 100644
--- a/arch/sparc/kernel/smp_64.c
+++ b/arch/sparc/kernel/smp_64.c
@@ -1014,7 +1014,7 @@ void flush_dcache_page_all(struct mm_struct *mm, struct page *page)
 }
 
 #ifdef CONFIG_KGDB
-void kgdb_roundup_cpus(unsigned long flags)
+void kgdb_roundup_cpus(void)
 {
 	smp_cross_call(&xcall_kgdb_capture, 0, 0, 0);
 }
diff --git a/arch/x86/kernel/kgdb.c b/arch/x86/kernel/kgdb.c
index 8e36f249646e..5db08425063e 100644
--- a/arch/x86/kernel/kgdb.c
+++ b/arch/x86/kernel/kgdb.c
@@ -422,21 +422,16 @@ static void kgdb_disable_hw_debug(struct pt_regs *regs)
 #ifdef CONFIG_SMP
 /**
  *	kgdb_roundup_cpus - Get other CPUs into a holding pattern
- *	@flags: Current IRQ state
  *
  *	On SMP systems, we need to get the attention of the other CPUs
  *	and get them be in a known state.  This should do what is needed
  *	to get the other CPUs to call kgdb_wait(). Note that on some arches,
  *	the NMI approach is not used for rounding up all the CPUs. For example,
- *	in case of MIPS, smp_call_function() is used to roundup CPUs. In
- *	this case, we have to make sure that interrupts are enabled before
- *	calling smp_call_function(). The argument to this function is
- *	the flags that will be used when restoring the interrupts. There is
- *	local_irq_save() call before kgdb_roundup_cpus().
+ *	in case of MIPS, smp_call_function() is used to roundup CPUs.
  *
  *	On non-SMP systems, this is not called.
  */
-void kgdb_roundup_cpus(unsigned long flags)
+void kgdb_roundup_cpus(void)
 {
 	apic->send_IPI_allbutself(APIC_DM_NMI);
 }
@@ -804,7 +799,7 @@ knl_write:
 				  (char *)bpt->saved_instr, BREAK_INSTR_SIZE);
 }
 
-struct kgdb_arch arch_kgdb_ops = {
+const struct kgdb_arch arch_kgdb_ops = {
 	/* Breakpoint instruction: */
 	.gdb_bpt_instr		= { 0xcc },
 	.flags			= KGDB_HW_BREAKPOINT,
diff --git a/include/linux/kgdb.h b/include/linux/kgdb.h
index e465bb15912d..fbf144aaa749 100644
--- a/include/linux/kgdb.h
+++ b/include/linux/kgdb.h
@@ -177,22 +177,28 @@ kgdb_arch_handle_exception(int vector, int signo, int err_code,
 			   struct pt_regs *regs);
 
 /**
+ *	kgdb_call_nmi_hook - Call kgdb_nmicallback() on the current CPU
+ *	@ignored: This parameter is only here to match the prototype.
+ *
+ *	If you're using the default implementation of kgdb_roundup_cpus()
+ *	this function will be called per CPU.  If you don't implement
+ *	kgdb_call_nmi_hook() a default will be used.
+ */
+
+extern void kgdb_call_nmi_hook(void *ignored);
+
+/**
  *	kgdb_roundup_cpus - Get other CPUs into a holding pattern
- *	@flags: Current IRQ state
  *
  *	On SMP systems, we need to get the attention of the other CPUs
  *	and get them into a known state.  This should do what is needed
  *	to get the other CPUs to call kgdb_wait(). Note that on some arches,
- *	the NMI approach is not used for rounding up all the CPUs. For example,
- *	in case of MIPS, smp_call_function() is used to roundup CPUs. In
- *	this case, we have to make sure that interrupts are enabled before
- *	calling smp_call_function(). The argument to this function is
- *	the flags that will be used when restoring the interrupts. There is
- *	local_irq_save() call before kgdb_roundup_cpus().
+ *	the NMI approach is not used for rounding up all the CPUs.  Normally
+ *	those architectures can just not implement this and get the default.
  *
  *	On non-SMP systems, this is not called.
  */
-extern void kgdb_roundup_cpus(unsigned long flags);
+extern void kgdb_roundup_cpus(void);
 
 /**
  *	kgdb_arch_set_pc - Generic call back to the program counter
@@ -281,7 +287,7 @@ struct kgdb_io {
 	int			is_console;
 };
 
-extern struct kgdb_arch		arch_kgdb_ops;
+extern const struct kgdb_arch		arch_kgdb_ops;
 
 extern unsigned long kgdb_arch_pc(int exception, struct pt_regs *regs);
 
diff --git a/kernel/debug/debug_core.c b/kernel/debug/debug_core.c
index 65c0f1363788..5cc608de6883 100644
--- a/kernel/debug/debug_core.c
+++ b/kernel/debug/debug_core.c
@@ -55,6 +55,7 @@
 #include <linux/mm.h>
 #include <linux/vmacache.h>
 #include <linux/rcupdate.h>
+#include <linux/irq.h>
 
 #include <asm/cacheflush.h>
 #include <asm/byteorder.h>
@@ -220,6 +221,62 @@ int __weak kgdb_skipexception(int exception, struct pt_regs *regs)
 	return 0;
 }
 
+#ifdef CONFIG_SMP
+
+/*
+ * Default (weak) implementation for kgdb_roundup_cpus
+ */
+
+static DEFINE_PER_CPU(call_single_data_t, kgdb_roundup_csd);
+
+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());
+}
+
+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;
+
+		csd->func = kgdb_call_nmi_hook;
+		ret = smp_call_function_single_async(cpu, csd);
+		if (ret)
+			kgdb_info[cpu].rounding_up = false;
+	}
+}
+
+#endif
+
 /*
  * Some architectures need cache flushes when we set/clear a
  * breakpoint:
@@ -535,6 +592,8 @@ return_normal:
 				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--;
@@ -593,7 +652,7 @@ return_normal:
 
 	/* Signal the other CPUs to enter kgdb_wait() */
 	else if ((!kgdb_single_step) && kgdb_do_roundup)
-		kgdb_roundup_cpus(flags);
+		kgdb_roundup_cpus();
 #endif
 
 	/*
@@ -667,6 +726,8 @@ kgdb_restore:
 	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--;
@@ -747,6 +808,8 @@ int kgdb_nmicallback(int cpu, void *regs)
 	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;
diff --git a/kernel/debug/debug_core.h b/kernel/debug/debug_core.h
index 127d9bc49fb4..b4a7c326d546 100644
--- a/kernel/debug/debug_core.h
+++ b/kernel/debug/debug_core.h
@@ -42,6 +42,7 @@ struct debuggerinfo_struct {
 	int			ret_state;
 	int			irq_depth;
 	int			enter_kgdb;
+	bool			rounding_up;
 };
 
 extern struct debuggerinfo_struct kgdb_info[];
diff --git a/kernel/debug/kdb/kdb_bt.c b/kernel/debug/kdb/kdb_bt.c
index 7921ae4fca8d..7e2379aa0a1e 100644
--- a/kernel/debug/kdb/kdb_bt.c
+++ b/kernel/debug/kdb/kdb_bt.c
@@ -186,7 +186,16 @@ kdb_bt(int argc, const char **argv)
 		kdb_printf("btc: cpu status: ");
 		kdb_parse("cpu\n");
 		for_each_online_cpu(cpu) {
-			sprintf(buf, "btt 0x%px\n", KDB_TSK(cpu));
+			void *kdb_tsk = KDB_TSK(cpu);
+
+			/* If a CPU failed to round up we could be here */
+			if (!kdb_tsk) {
+				kdb_printf("WARNING: no task for cpu %ld\n",
+					   cpu);
+				continue;
+			}
+
+			sprintf(buf, "btt 0x%px\n", kdb_tsk);
 			kdb_parse(buf);
 			touch_nmi_watchdog();
 		}
diff --git a/kernel/debug/kdb/kdb_debugger.c b/kernel/debug/kdb/kdb_debugger.c
index 15e1a7af5dd0..53a0df6e4d92 100644
--- a/kernel/debug/kdb/kdb_debugger.c
+++ b/kernel/debug/kdb/kdb_debugger.c
@@ -118,13 +118,6 @@ int kdb_stub(struct kgdb_state *ks)
 	kdb_bp_remove();
 	KDB_STATE_CLEAR(DOING_SS);
 	KDB_STATE_SET(PAGER);
-	/* zero out any offline cpu data */
-	for_each_present_cpu(i) {
-		if (!cpu_online(i)) {
-			kgdb_info[i].debuggerinfo = NULL;
-			kgdb_info[i].task = NULL;
-		}
-	}
 	if (ks->err_code == DIE_OOPS || reason == KDB_REASON_OOPS) {
 		ks->pass_exception = 1;
 		KDB_FLAG_SET(CATASTROPHIC);
diff --git a/kernel/debug/kdb/kdb_main.c b/kernel/debug/kdb/kdb_main.c
index d72b32c66f7d..82a3b32a7cfc 100644
--- a/kernel/debug/kdb/kdb_main.c
+++ b/kernel/debug/kdb/kdb_main.c
@@ -658,7 +658,7 @@ static void kdb_cmderror(int diag)
  */
 struct defcmd_set {
 	int count;
-	int usable;
+	bool usable;
 	char *name;
 	char *usage;
 	char *help;
@@ -666,7 +666,7 @@ struct defcmd_set {
 };
 static struct defcmd_set *defcmd_set;
 static int defcmd_set_count;
-static int defcmd_in_progress;
+static bool defcmd_in_progress;
 
 /* Forward references */
 static int kdb_exec_defcmd(int argc, const char **argv);
@@ -676,9 +676,9 @@ static int kdb_defcmd2(const char *cmdstr, const char *argv0)
 	struct defcmd_set *s = defcmd_set + defcmd_set_count - 1;
 	char **save_command = s->command;
 	if (strcmp(argv0, "endefcmd") == 0) {
-		defcmd_in_progress = 0;
+		defcmd_in_progress = false;
 		if (!s->count)
-			s->usable = 0;
+			s->usable = false;
 		if (s->usable)
 			/* macros are always safe because when executed each
 			 * internal command re-enters kdb_parse() and is
@@ -695,7 +695,7 @@ static int kdb_defcmd2(const char *cmdstr, const char *argv0)
 	if (!s->command) {
 		kdb_printf("Could not allocate new kdb_defcmd table for %s\n",
 			   cmdstr);
-		s->usable = 0;
+		s->usable = false;
 		return KDB_NOTIMP;
 	}
 	memcpy(s->command, save_command, s->count * sizeof(*(s->command)));
@@ -737,7 +737,7 @@ static int kdb_defcmd(int argc, const char **argv)
 	       defcmd_set_count * sizeof(*defcmd_set));
 	s = defcmd_set + defcmd_set_count;
 	memset(s, 0, sizeof(*s));
-	s->usable = 1;
+	s->usable = true;
 	s->name = kdb_strdup(argv[1], GFP_KDB);
 	if (!s->name)
 		goto fail_name;
@@ -756,7 +756,7 @@ static int kdb_defcmd(int argc, const char **argv)
 		s->help[strlen(s->help)-1] = '\0';
 	}
 	++defcmd_set_count;
-	defcmd_in_progress = 1;
+	defcmd_in_progress = true;
 	kfree(save_defcmd_set);
 	return 0;
 fail_help: