1 files changed, 46 insertions, 24 deletions

diff --git a/kernel/debug/debug_core.c b/kernel/debug/debug_core.c
index 5cc608de6883..2b7c9b67931d 100644
--- a/kernel/debug/debug_core.c
+++ b/kernel/debug/debug_core.c
@@ -441,6 +441,37 @@ setundefined:
 	return 0;
 }
 
+#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
@@ -580,6 +611,9 @@ cpu_loop:
 				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;
@@ -787,11 +821,8 @@ out:
 }
 
 /*
- * GDB places a breakpoint at this function to know dynamically
- * loaded objects. It's not defined static so that only one instance with this
- * name exists in the kernel.
+ * 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)
 {
@@ -896,30 +927,25 @@ static struct sysrq_key_op sysrq_dbg_op = {
 };
 #endif
 
-static int kgdb_panic_event(struct notifier_block *self,
-			    unsigned long val,
-			    void *data)
+void kgdb_panic(const char *msg)
 {
+	if (!kgdb_io_module_registered)
+		return;
+
 	/*
-	 * Avoid entering the debugger if we were triggered due to a panic
-	 * We don't want to get stuck waiting for input from user in such case.
-	 * panic_timeout indicates the system should automatically
+	 * 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 NOTIFY_DONE;
+		return;
 
 	if (dbg_kdb_mode)
-		kdb_printf("PANIC: %s\n", (char *)data);
+		kdb_printf("PANIC: %s\n", msg);
+
 	kgdb_breakpoint();
-	return NOTIFY_DONE;
 }
 
-static struct notifier_block kgdb_panic_event_nb = {
-       .notifier_call	= kgdb_panic_event,
-       .priority	= INT_MAX,
-};
-
 void __weak kgdb_arch_late(void)
 {
 }
@@ -968,8 +994,6 @@ static void kgdb_register_callbacks(void)
 			kgdb_arch_late();
 		register_module_notifier(&dbg_module_load_nb);
 		register_reboot_notifier(&dbg_reboot_notifier);
-		atomic_notifier_chain_register(&panic_notifier_list,
-					       &kgdb_panic_event_nb);
 #ifdef CONFIG_MAGIC_SYSRQ
 		register_sysrq_key('g', &sysrq_dbg_op);
 #endif
@@ -983,16 +1007,14 @@ static void kgdb_register_callbacks(void)
 static void kgdb_unregister_callbacks(void)
 {
 	/*
-	 * When this routine is called KGDB should unregister from the
-	 * panic handler and clean up, making sure it is not handling any
+	 * 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);
-		atomic_notifier_chain_unregister(&panic_notifier_list,
-					       &kgdb_panic_event_nb);
 		kgdb_arch_exit();
 #ifdef CONFIG_MAGIC_SYSRQ
 		unregister_sysrq_key('g', &sysrq_dbg_op);