kdb: Fix "btc <cpu>" crash if the CPU didn't round up

I noticed that when I did "btc <cpu>" and the CPU I passed in hadn't
rounded up that I'd crash.  I was going to copy the same fix from
commit 162bc7f5 ("kdb: Don't back trace on a cpu that didn't round
up") into the "not all the CPUs" case, but decided it'd be better to
clean things up a little bit.

This consolidates the two code paths.  It is _slightly_ wasteful in in
that the checks for "cpu" being too small or being offline isn't
really needed when we're iterating over all online CPUs, but that
really shouldn't hurt.  Better to have the same code path.

While at it, eliminate at least one slightly ugly (and totally
needless) recursive use of kdb_parse().
Signed-off-by: Douglas Anderson <dianders@chromium.org>
Acked-by: Will Deacon <will@kernel.org>
Signed-off-by: Daniel Thompson <daniel.thompson@linaro.org>

kernel/debug/kdb/kdb_bt.c

@@ -101,6 +101,27 @@ kdb_bt1(struct task_struct *p, unsigned long mask, bool btaprompt)
 	return 0;
 }
 
+static void
+kdb_bt_cpu(unsigned long cpu)
+{
+	struct task_struct *kdb_tsk;
+
+	if (cpu >= num_possible_cpus() || !cpu_online(cpu)) {
+		kdb_printf("WARNING: no process for cpu %ld\n", cpu);
+		return;
+	}
+
+	/* If a CPU failed to round up we could be here */
+	kdb_tsk = KDB_TSK(cpu);
+	if (!kdb_tsk) {
+		kdb_printf("WARNING: no task for cpu %ld\n", cpu);
+		return;
+	}
+
+	kdb_set_current_task(kdb_tsk);
+	kdb_bt1(kdb_tsk, ~0UL, false);
+}
+
 int
 kdb_bt(int argc, const char **argv)
 {
@@ -161,7 +182,6 @@ kdb_bt(int argc, const char **argv)
 	} else if (strcmp(argv[0], "btc") == 0) {
 		unsigned long cpu = ~0;
 		struct task_struct *save_current_task = kdb_current_task;
-		char buf[80];
 		if (argc > 1)
 			return KDB_ARGCOUNT;
 		if (argc == 1) {
@@ -169,35 +189,22 @@ kdb_bt(int argc, const char **argv)
 			if (diag)
 				return diag;
 		}
-		/* Recursive use of kdb_parse, do not use argv after
-		 * this point */
-		argv = NULL;
 		if (cpu != ~0) {
-			if (cpu >= num_possible_cpus() || !cpu_online(cpu)) {
-				kdb_printf("no process for cpu %ld\n", cpu);
-				return 0;
-			}
-			sprintf(buf, "btt 0x%px\n", KDB_TSK(cpu));
-			kdb_parse(buf);
-			return 0;
-		}
-		kdb_printf("btc: cpu status: ");
-		kdb_parse("cpu\n");
-		for_each_online_cpu(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;
+			kdb_bt_cpu(cpu);
+		} else {
+			/*
+			 * Recursive use of kdb_parse, do not use argv after
+			 * this point.
+			 */
+			argv = NULL;
+			kdb_printf("btc: cpu status: ");
+			kdb_parse("cpu\n");
+			for_each_online_cpu(cpu) {
+				kdb_bt_cpu(cpu);
+				touch_nmi_watchdog();
 			}
-
-			sprintf(buf, "btt 0x%px\n", kdb_tsk);
-			kdb_parse(buf);
-			touch_nmi_watchdog();
+			kdb_set_current_task(save_current_task);
 		}
-		kdb_set_current_task(save_current_task);
 		return 0;
 	} else {
 		if (argc) {