[Crash-utility] [RFC/PATCH] s390x: Add live dump detection

[Michael Holzheu]

Hello Dave,

On Mon, 23 Apr 2012 08:50:02 -0400 (EDT)
Dave Anderson <anderson at redhat.com> wrote:

[snip]

> 
> 
> Question: how does that code path ever get run?  

Interesting...

I only tested the patch on a live dump and not on the live system
with /dev/mem. Therefore I did not see that. On a live system, as you
described it, the s390x.c code is not used.

> 
> If you try a "bt" on an active task on a live system, it would 
> print the "(active)" here in back_trace(), prior to calling into
> the machine-specific backtrace function:
> 
>         if (ACTIVE() && !(bt->flags & BT_EFRAME_SEARCH) &&
>             ((bt->task == tt->this_task) ||
> is_task_active(bt->task))) {
> 
>                 if (BT_REFERENCE_CHECK(bt) ||
>                     bt->flags &
> (BT_TEXT_SYMBOLS_PRINT|BT_TEXT_SYMBOLS_NOPRINT)) return;
> 
>                 if (!(bt->flags &
>                     (BT_KSTACKP|BT_TEXT_SYMBOLS|BT_TEXT_SYMBOLS_ALL)))
>                         fprintf(fp, "(active)\n");
> 
>                 if (!(bt->flags &
> (BT_TEXT_SYMBOLS|BT_TEXT_SYMBOLS_ALL))) return;
>         }
> 
> Note the "bt -[tT]" options should be allowed even if the task is
> active.

So the check should be done in kernel.c and not in s390x.c.

Would the following patch be better?
---
 kernel.c |    2 +-
 s390x.c  |    4 ----
 2 files changed, 1 insertion(+), 5 deletions(-)

--- a/kernel.c
+++ b/kernel.c
@@ -2245,7 +2245,7 @@ back_trace(struct bt_info *bt)
 		return;
 	}
 
-	if (ACTIVE() && !(bt->flags & BT_EFRAME_SEARCH) && 
+	if (LIVE() && !(bt->flags & BT_EFRAME_SEARCH) && 
             ((bt->task == tt->this_task) || is_task_active(bt->task))) {
 
 		if (BT_REFERENCE_CHECK(bt) ||
--- a/s390x.c
+++ b/s390x.c
@@ -1092,10 +1092,6 @@ static void s390x_back_trace_cmd(struct 
 	 * Print lowcore and print interrupt stacks when task has cpu
 	 */
 	if (s390x_has_cpu(bt)) {
-		if (ACTIVE()) {
-			fprintf(fp,"(active)\n");
-			return;
-		}
 		s390x_get_lowcore(bt, lowcore);
 		psw_flags = ULONG(lowcore + OFFSET(s390_lowcore_psw_save_area));