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: [email protected]
Fixes: 02205a6752f2 ("tracing: Add support for 'field variables'")
Reported-by: [email protected]
Closes: https://lore.kernel.org/all/[email protected]/
Signed-off-by: Donggeun Yoo <[email protected]>
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
