On Fri, 28 Aug 2026 09:23:57 -0400 Steven Rostedt <[email protected]> wrote:
> On Thu, 27 Aug 2026 20:28:59 -0400 > Steven Rostedt <[email protected]> wrote: > > > I see what the problem is. I guess you were creating and removing trace > > instances while reading available_events. All files that are part of an > > instance needs to get a reference counter on the trace instance when > > opened. This prevents the instance from being freed when there are > > opened files in it. I see that the available_events file doesn't take > > that reference which will allow its instance to be freed while another > > task has its content opened. When it reads that content, it will > > trigger the bug you see. > > It's not available_events, it's the two new files that were added that > didn't take a reference: > > show_event_filters and show_event_triggers > > This should fix it: > I updated the selftests with this: diff --git a/tools/testing/selftests/ftrace/test.d/instances/instance-event.tc b/tools/testing/selftests/ftrace/test.d/instances/instance-event.tc index 42422e425107..1e3f27d6998b 100644 --- a/tools/testing/selftests/ftrace/test.d/instances/instance-event.tc +++ b/tools/testing/selftests/ftrace/test.d/instances/instance-event.tc @@ -43,6 +43,13 @@ instance_set() { done 2> /dev/null } +instance_cat() { + while :; do + cat foo/show_event_filters + cat foo/show_event_triggers + done 2> /dev/null +} + instance_slam & p1=$! echo $p1 @@ -55,14 +62,19 @@ instance_read & p3=$! echo $p3 +instance_cat & +p4=$! +echo $p4 + sleep 1 +kill -1 $p4 kill -1 $p3 kill -1 $p2 kill -1 $p1 echo "Wait for processes to finish" -wait $p1 $p2 $p3 +wait $p1 $p2 $p3 $p4 echo "all processes finished, wait for cleanup" sleep 1 And it was also able to reproduce the issue. With the applied fix, it doesn't trigger anymore. I'll write up a proper patch. -- Steve
