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tracing: Unregister field variable histograms when the command fails

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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
Link: https://patch.msgid.link/20260914104036.1768529-1-donggeunyoo.kernel@gmail.com
Fixes: 02205a6752 ("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 <donggeunyoo.kernel@gmail.com>
Assisted-by: Claude:claude-fable-5
Signed-off-by: Steven Rostedt <rostedt@goodmis.org>
This commit is contained in:
Donggeun Yoo 2026-09-14 19:40:36 +09:00 committed by Steven Rostedt
parent 18bb005845
commit 91c14d6c13
1 changed files with 6 additions and 6 deletions
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12
kernel/trace/trace_events_hist.c
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@ -3137,20 +3137,18 @@ 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;
}
@ -6983,6 +6981,8 @@ 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;
}