An action that names a field on another event needs that field as a variable, so create_field_var_hist() registers a second hist trigger on that event to provide it, and records it in target_hist_data->field_var_hists[]. If a later part of the same command fails, create_actions() returns an error and event_hist_trigger_parse() jumps to out_free. The write fails with -EINVAL and sched_switch gets no trigger, but: # echo 'hist:keys=pid:ts0=common_timestamp.usecs' >> \ events/sched/sched_waking/trigger # echo 'my_synth u64 lat; int a; int b' >> synthetic_events # echo 'hist:keys=next_pid:wakeup_lat=common_timestamp.usecs-$ts0:\ onmatch(sched.sched_waking).my_synth($wakeup_lat,prio,nosuchfld)'\ >> events/sched/sched_switch/trigger # cat events/sched/sched_waking/trigger hist:keys=pid:vals=hitcount:ts0=common_timestamp.usecs:sort=hitcount:size=2048:clock=global [active] hist:keys=pid:vals=hitcount:synthetic_prio=prio:sort=hitcount:size=2048 [active] The second histogram is the one created for 'prio'. It is still active and still counting. out_free reaches destroy_field_var_hists(), which frees the field_var_hists[] entries, but never unregister_field_var_hists(), which is what removes the triggers and runs only from event_hist_trigger_free(). The entry is freed and the trigger is left with nothing tracking it. Unregister the field variable histograms in out_free as well, and record each one as soon as its trigger is registered rather than after the lookup that follows it, so no exit can leave a registered trigger untracked. The entry then belongs to field_var_hists[] and is released by destroy_field_var_hists(), so freeing it on that exit would be a double free. Cc: stable@vger.kernel.org Fixes: 02205a6752f2 ("tracing: Add support for 'field variables'") Reported-by: sashiko-bot@kernel.org Closes: https://lore.kernel.org/all/20260913204302.DB2551F000FF@smtp.kernel.org/ Signed-off-by: Donggeun Yoo Assisted-by: Claude:claude-fable-5 --- Tested under QEMU on 704340f1cd0d, x86_64, KASAN + PROVE_LOCKING, 2 vCPU, unfixed arm first. command before after valid onmatch on another event's field works works removing that trigger works works onmatch with a trailing bad field orphan clean the same bad command, five more times orphan clean two field variables, then a bad field 2 orphans clean '!hist' that matches nothing clean clean orphan = an extra [active] histogram left on the matched event. ftracetest test.d/trigger: identical per-test verdicts on both arms. trigger-synthetic-event-dynstring.tc fails on both because busybox execs its ping applet as /proc/self/exe, so the test's grep cannot match. The exit that reports a missing synthetic variable is not reachable through onmatch, so no run covers it. kernel/trace/trace_events_hist.c | 12 ++++++------ 1 file changed, 6 insertions(+), 6 deletions(-) diff --git a/kernel/trace/trace_events_hist.c b/kernel/trace/trace_events_hist.c index 8af97fd4ee2d..90e6e3990c25 100644 --- a/kernel/trace/trace_events_hist.c +++ b/kernel/trace/trace_events_hist.c @@ -3134,20 +3134,18 @@ create_field_var_hist(struct hist_trigger_data *target_hist_data, kfree(cmd); + n = target_hist_data->n_field_var_hists; + target_hist_data->field_var_hists[n] = var_hist; + target_hist_data->n_field_var_hists++; + /* If we can't find the variable, something went wrong */ event_var = find_synthetic_field_var(target_hist_data, subsys_name, event_name, field_name); if (IS_ERR_OR_NULL(event_var)) { - kfree(var_hist->cmd); - kfree(var_hist); hist_err(tr, HIST_ERR_SYNTH_VAR_NOT_FOUND, errpos(field_name)); return ERR_PTR(-EINVAL); } - n = target_hist_data->n_field_var_hists; - target_hist_data->field_var_hists[n] = var_hist; - target_hist_data->n_field_var_hists++; - return event_var; } @@ -6980,6 +6978,8 @@ static int event_hist_trigger_parse(struct event_command *cmd_ops, trigger_data_free(trigger_data); + unregister_field_var_hists(hist_data); + destroy_hist_data(hist_data); goto out; } -- 2.53.0