| Message ID | 20250407154139.69955768@gandalf.local.home (mailing list archive) |
|---|---|
| State | Accepted |
| Commit | e1a453a57bc76be678bd746f84e3d73f378a9511 |
| Headers | show |
| Series | tracing: Do not add length to print format in synthetic events | expand |
On Mon, 7 Apr 2025 15:41:39 -0400 Steven Rostedt <rostedt@goodmis.org> wrote: > From: Steven Rostedt <rostedt@goodmis.org> > > The following causes a vsnprintf fault: > > # 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 > > Because the synthetic event's "wakee" field is created as a dynamic string > (even though the string copied is not). The print format to print the > dynamic string changed from "%*s" to "%s" because another location > (__set_synth_event_print_fmt()) exported this to user space, and user > space did not need that. But it is still used in print_synth_event(), and > the output looks like: > > <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 > bash-880 [002] d..5. 193.811371: wake_lat: wakee=(efault)kworker/u35:2delta=21 > <idle>-0 [001] d..5. 193.811516: wake_lat: wakee=(efault)sshd-sessiondelta=129 > sshd-session-879 [001] d..5. 193.967576: wake_lat: wakee=(efault)kworker/u34:5delta=50 > > The length isn't needed as the string is always nul terminated. Just print > the string and not add the length (which was hard coded to the max string > length anyway). > Good catch! Acked-by: Masami Hiramatsu (Google) <mhiramat@kernel.org> Thanks! > Cc: stable@vger.kernel.org > Fixes: 4d38328eb442d ("tracing: Fix synth event printk format for str fields"); > 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 969f48742d72..33cfbd4ed76d 100644 > --- a/kernel/trace/trace_events_synth.c > +++ b/kernel/trace/trace_events_synth.c > @@ -370,7 +370,6 @@ static enum print_line_t print_synth_event(struct trace_iterator *iter, > union trace_synth_field *data = &entry->fields[n_u64]; > > trace_seq_printf(s, print_fmt, se->fields[i]->name, > - STR_VAR_LEN_MAX, > (char *)entry + data->as_dynamic.offset, > i == se->n_fields - 1 ? "" : " "); > n_u64++; > -- > 2.47.2 >
diff --git a/kernel/trace/trace_events_synth.c b/kernel/trace/trace_events_synth.c index 969f48742d72..33cfbd4ed76d 100644 --- a/kernel/trace/trace_events_synth.c +++ b/kernel/trace/trace_events_synth.c @@ -370,7 +370,6 @@ static enum print_line_t print_synth_event(struct trace_iterator *iter, union trace_synth_field *data = &entry->fields[n_u64]; trace_seq_printf(s, print_fmt, se->fields[i]->name, - STR_VAR_LEN_MAX, (char *)entry + data->as_dynamic.offset, i == se->n_fields - 1 ? "" : " "); n_u64++;