[Crash-utility] [PATCH] Fix list '-B' option incorrect loop 0 with single embedded list_head

[Dave Wysochanski]

Commit 6596f1121b added a '-B' option to the list command to allow
more efficient enumeration of longer lists.  Unfortunately there
is a small bug with this option where it may incorrectly flag a
loop length of '0' on list of length 1. It is impossible to have
a loop of length 0 and we can easily avoid the bug by looking at
'count'.

Example:
crash> mutex.wait_list 0xffff8801070d6958
  wait_list = 0xffff88010802bd08
crash> struct -o mutex.wait_list
struct mutex {
   [8] struct list_head *wait_list;
}
crash> list -B -H 0xffff8801070d6960 -o mutex_waiter.list -s mutex_waiter.task
ffff88010802bd08
  task = 0xffff88013e7d7520
list: loop detected, loop length: 0
crash> list -H 0xffff8801070d6960 -o mutex_waiter.list -s mutex_waiter.task
ffff88010802bd08
  task = 0xffff88013e7d7520
crash>

Fixes: 6596f1121b
Signed-off-by: Dave Wysochanski <dwysocha at redhat.com>
---
 tools.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/tools.c b/tools.c
index f32e62f..85c8166 100644
--- a/tools.c
+++ b/tools.c
@@ -4146,7 +4146,7 @@ do_list_no_hash(struct list_data *ld)
 			return -1;
 
 		if (!brent_loop_detect) {
-			if (brent_x == brent_y) {
+			if (count > 1 && brent_x == brent_y) {
 				brent_loop_detect = 1;
 				error(INFO, "loop detected, loop length: %ld\n", brent_lambda);
 				/* reset x and y to start; advance y loop length */
-- 
1.8.3.1