kernel-shark: The graph widget must follow the active marker

The "Graph follows" checkbox controls if the Graph widget follows or not
the change of the Active marker made from the View widget (the text data
table).
In the same time, when the user clicks on the checkbox switching it from
Unchecked to Checked, a signal is send to the Graph widget to make sure
that it will visualize the current position of the Active marker. When
sending this signal, we currently use the iterator of the search results
list, which is wrong because of two reasons. First, the  search results
list can be empty, which will trigger a segmentation fault, as reported
by Valentin Schneider. But even more important is that nothing guarantees
that when the checkbox is checked, the marker and the iterator both point
to the same trace entry. Note that the iteration over the search results
is only one of the possible ways to change the marker.

Bugzilla: https://bugzilla.kernel.org/show_bug.cgi?id=204139
Link: http://lore.kernel.org/linux-trace-devel/20190715132042.5154-2-y.karadz@gmail.com

Reported-By: Valentin Schneider <valentin.schneider@arm.com>
Tested-by: Valentin Schneider <valentin.schneider@arm.com>
Signed-off-by: Yordan Karadzhov (VMware) <y.karadz@gmail.com>
Signed-off-by: Steven Rostedt (VMware) <rostedt@goodmis.org>

1 files changed, 4 insertions, 3 deletions

diff --git a/kernel-shark/src/KsTraceViewer.cpp b/kernel-shark/src/KsTraceViewer.cpp
index 05977c3d..89e5dba2 100644
--- a/kernel-shark/src/KsTraceViewer.cpp
+++ b/kernel-shark/src/KsTraceViewer.cpp
@@ -285,10 +285,11 @@ void KsTraceViewer::_searchEditText(const QString &text)
 
 void KsTraceViewer::_graphFollowsChanged(int state)
 {
-	_graphFollows = (bool) state;
+	int row = selectedRow();
 
-	if (_graphFollows && _searchDone())
-		emit select(*_it); // Send a signal to the Graph widget.
+	_graphFollows = (bool) state;
+	if (_graphFollows && row != KS_NO_ROW_SELECTED)
+		emit select(row); // Send a signal to the Graph widget.
 }
 
 void KsTraceViewer::_search()