From: Steven Rostedt <rostedt@goodmis.org>
Date: Thu, 4 Dec 2025 20:19:35 +0000 (-0500)
Subject: tracing: Fix fixed array of synthetic event
X-Git-Url: http://git.ipfire.org/?a=commitdiff_plain;h=47ef834209e5981f443240d8a8b45bf680df22aa;p=thirdparty%2Flinux.git

tracing: Fix fixed array of synthetic event

The commit 4d38328eb442d ("tracing: Fix synth event printk format for str
fields") replaced "%.*s" with "%s" but missed removing the number size of
the dynamic and static strings. The commit e1a453a57bc7 ("tracing: Do not
add length to print format in synthetic events") fixed the dynamic part
but did not fix the static part. That is, with the commands:

  # echo 's:wake_lat char[] wakee; u64 delta;' >> /sys/kernel/tracing/dynamic_events
  # echo 'hist:keys=pid:ts=common_timestamp.usecs if !(common_flags & 0x18)' > /sys/kernel/tracing/events/sched/sched_waking/trigger
  # echo 'hist:keys=next_pid:delta=common_timestamp.usecs-$ts:onmatch(sched.sched_waking).trace(wake_lat,next_comm,$delta)' > /sys/kernel/tracing/events/sched/sched_switch/trigger

That caused the output of:

          <idle>-0       [001] d..5.   193.428167: wake_lat: wakee=(efault)sshd-sessiondelta=155
    sshd-session-879     [001] d..5.   193.811080: wake_lat: wakee=(efault)kworker/u34:5delta=58
          <idle>-0       [002] d..5.   193.811198: wake_lat: wakee=(efault)bashdelta=91

The commit e1a453a57bc7 fixed the part where the synthetic event had
"char[] wakee". But if one were to replace that with a static size string:

  # echo 's:wake_lat char[16] wakee; u64 delta;' >> /sys/kernel/tracing/dynamic_events

Where "wakee" is defined as "char[16]" and not "char[]" making it a static
size, the code triggered the "(efaul)" again.

Remove the added STR_VAR_LEN_MAX size as the string is still going to be
nul terminated.

Cc: stable@vger.kernel.org
Cc: Masami Hiramatsu <mhiramat@kernel.org>
Cc: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Cc: Douglas Raillard <douglas.raillard@arm.com>
Link: https://patch.msgid.link/20251204151935.5fa30355@gandalf.local.home
Fixes: e1a453a57bc7 ("tracing: Do not add length to print format in synthetic events")
Signed-off-by: Steven Rostedt (Google) <rostedt@goodmis.org>
---

diff --git a/kernel/trace/trace_events_synth.c b/kernel/trace/trace_events_synth.c
index 2f19bbe73d274..4554c458b78c4 100644
--- a/kernel/trace/trace_events_synth.c
+++ b/kernel/trace/trace_events_synth.c
@@ -375,7 +375,6 @@ static enum print_line_t print_synth_event(struct trace_iterator *iter,
 				n_u64++;
 			} else {
 				trace_seq_printf(s, print_fmt, se->fields[i]->name,
-						 STR_VAR_LEN_MAX,
 						 (char *)&entry->fields[n_u64].as_u64,
 						 i == se->n_fields - 1 ? "" : " ");
 				n_u64 += STR_VAR_LEN_MAX / sizeof(u64);