[Crash-utility] [PATCH] crash: bt: Introduce -p option

[Aaron Tomlin]

The purpose of this patch is to provide a -p option to generate a stack
trace of the panic task, if available. It might be useful if the current
context is changed with the 'set' command.

This option is not supported under a live system or live dump.

Signed-off-by: Aaron Tomlin <atomlin at redhat.com>
---
 help.c   |  4 +++-
 kernel.c | 19 +++++++++++++++----
 2 files changed, 18 insertions(+), 5 deletions(-)

diff --git a/help.c b/help.c
index c0c750f..581e616 100644
--- a/help.c
+++ b/help.c
@@ -1789,13 +1789,15 @@ NULL
 char *help_bt[] = {
 "bt",
 "backtrace",
-"[-a|-c cpu(s)|-g|-r|-t|-T|-l|-e|-E|-f|-F|-o|-O|-v] [-R ref] [-s [-x|d]]"
+"[-a|-c cpu(s)|-g|-r|-t|-T|-l|-e|-E|-f|-F|-o|-O|-v|-p] [-R ref] [-s [-x|d]]"
 "\n     [-I ip] [-S sp] [pid | task]",
 "  Display a kernel stack backtrace.  If no arguments are given, the stack",
 "  trace of the current context will be displayed.\n",
 "       -a  displays the stack traces of the active task on each CPU.",
 "           (only applicable to crash dumps)",
 "       -A  same as -a, but also displays vector registers (S390X only).",
+"       -p  display the stack trace of the panic task only.",
+"           (only applicable to crash dumps)",
 "   -c cpu  display the stack trace of the active task on one or more CPUs,",
 "           which can be specified using the format \"3\", \"1,8,9\", \"1-23\",",
 "           or \"1,8,9-14\". (only applicable to crash dumps)",
diff --git a/kernel.c b/kernel.c
index f5960fc..e1f0b7e 100644
--- a/kernel.c
+++ b/kernel.c
@@ -2402,7 +2402,7 @@ cmd_bt(void)
 	int i, c;
 	ulong value, *cpus;
         struct task_context *tc;
-	int subsequent, active;
+	int subsequent, active, panic;
 	struct stack_hook hook;
 	struct bt_info bt_info, bt_setup, *bt;
 	struct reference reference;
@@ -2412,7 +2412,7 @@ cmd_bt(void)
 
 	tc = NULL;
 	cpus = NULL;
-	subsequent = active = 0;
+	subsequent = active = panic = 0;
 	hook.eip = hook.esp = 0;
 	refptr = 0;
 	bt = &bt_info;
@@ -2421,7 +2421,7 @@ cmd_bt(void)
 	if (kt->flags & USE_OPT_BT)
 		bt->flags |= BT_OPT_BACK_TRACE;
 
-	while ((c = getopt(argcnt, args, "D:fFI:S:c:aAloreEgstTdxR:Ov")) != EOF) {
+	while ((c = getopt(argcnt, args, "D:fFI:S:c:aAloreEgstTdxR:Ovp")) != EOF) {
                 switch (c)
 		{
 		case 'f':
@@ -2609,6 +2609,14 @@ cmd_bt(void)
 				option_not_supported(c);
 			check_stack_overflow();
 			return;
+		case 'p':
+			if (LIVE())
+				error(FATAL,
+				    "-p option not supported on a live system or live dump\n");
+			if (!tt->panic_task)
+				error(FATAL, "no panic task found!\n");
+			panic++;
+			break;
 
 		default:
 			argerrs++;
@@ -2748,7 +2756,10 @@ cmd_bt(void)
 			tgid = task_tgid(CURRENT_TASK());
 			DO_THREAD_GROUP_BACKTRACE();
 		} else {
-			tc = CURRENT_CONTEXT();
+			if (panic)
+				tc = task_to_context(tt->panic_task);
+			else
+				tc = CURRENT_CONTEXT();
 			DO_TASK_BACKTRACE();
 		}
 		return;
-- 
2.20.1