From: Steven Rostedt rostedt@goodmis.org

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 --- kernel/trace/trace_events_synth.c | 1 - 1 file changed, 1 deletion(-)

diff --git a/kernel/trace/trace_events_synth.c b/kernel/trace/trace_events_synth.c index 2f19bbe73d27..4554c458b78c 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);