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tracing: Allow perf to read synthetic events

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Currently, perf can not enable synthetic events. When it does, it either
causes a warning in the kernel or errors with "no such device".

Add the necessary code to allow perf to also attach to synthetic events.

Cc: Masami Hiramatsu <mhiramat@kernel.org>
Cc: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Cc: Arnaldo Carvalho de Melo <acme@kernel.org>
Cc: Jiri Olsa <jolsa@kernel.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Link: https://patch.msgid.link/20260513150007.3b280e87@gandalf.local.home
Reported-by: Ian Rogers <irogers@google.com>
Acked-by: Namhyung Kim <namhyung@kernel.org>
Signed-off-by: Steven Rostedt (Google) <rostedt@goodmis.org>
This commit is contained in:
Steven Rostedt 2026-05-13 15:00:07 -04:00
parent 5307505fe7
commit bb4613842e
1 changed files with 94 additions and 27 deletions
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121
kernel/trace/trace_events_synth.c
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@ -499,28 +499,19 @@ static unsigned int trace_stack(struct synth_trace_event *entry,
return len;
}
static void trace_event_raw_event_synth(void *__data,
u64 *var_ref_vals,
unsigned int *var_ref_idx)
static __always_inline int get_field_size(struct synth_event *event,
u64 *var_ref_vals,
unsigned int *var_ref_idx)
{
unsigned int i, n_u64, val_idx, len, data_size = 0;
struct trace_event_file *trace_file = __data;
struct synth_trace_event *entry;
struct trace_event_buffer fbuffer;
struct trace_buffer *buffer;
struct synth_event *event;
int fields_size = 0;
event = trace_file->event_call->data;
if (trace_trigger_soft_disabled(trace_file))
return;
int fields_size;
fields_size = event->n_u64 * sizeof(u64);
for (i = 0; i < event->n_dynamic_fields; i++) {
for (int i = 0; i < event->n_dynamic_fields; i++) {
unsigned int field_pos = event->dynamic_fields[i]->field_pos;
char *str_val;
int val_idx;
int len;
val_idx = var_ref_idx[field_pos];
str_val = (char *)(long)var_ref_vals[val_idx];
@ -535,18 +526,18 @@ static void trace_event_raw_event_synth(void *__data,
fields_size += len;
}
return fields_size;
}
/*
* Avoid ring buffer recursion detection, as this event
* is being performed within another event.
*/
buffer = trace_file->tr->array_buffer.buffer;
guard(ring_buffer_nest)(buffer);
entry = trace_event_buffer_reserve(&fbuffer, trace_file,
sizeof(*entry) + fields_size);
if (!entry)
return;
static __always_inline void write_synth_entry(struct synth_event *event,
struct synth_trace_event *entry,
u64 *var_ref_vals,
unsigned int *var_ref_idx)
{
int data_size = 0;
int i, n_u64;
int val_idx;
int len;
for (i = 0, n_u64 = 0; i < event->n_fields; i++) {
val_idx = var_ref_idx[i];
@ -587,10 +578,83 @@ static void trace_event_raw_event_synth(void *__data,
n_u64++;
}
}
}
static void trace_event_raw_event_synth(void *__data,
u64 *var_ref_vals,
unsigned int *var_ref_idx)
{
struct trace_event_file *trace_file = __data;
struct synth_trace_event *entry;
struct trace_event_buffer fbuffer;
struct trace_buffer *buffer;
struct synth_event *event;
int fields_size;
event = trace_file->event_call->data;
if (trace_trigger_soft_disabled(trace_file))
return;
fields_size = get_field_size(event, var_ref_vals, var_ref_idx);
/*
* Avoid ring buffer recursion detection, as this event
* is being performed within another event.
*/
buffer = trace_file->tr->array_buffer.buffer;
guard(ring_buffer_nest)(buffer);
entry = trace_event_buffer_reserve(&fbuffer, trace_file,
sizeof(*entry) + fields_size);
if (!entry)
return;
write_synth_entry(event, entry, var_ref_vals, var_ref_idx);
trace_event_buffer_commit(&fbuffer);
}
#ifdef CONFIG_PERF_EVENTS
static void perf_event_raw_event_synth(void *__data,
u64 *var_ref_vals,
unsigned int *var_ref_idx)
{
struct trace_event_call *call = __data;
struct synth_trace_event *entry;
struct hlist_head *perf_head;
struct synth_event *event;
struct pt_regs *regs;
int fields_size;
size_t size;
int context;
event = call->data;
perf_head = this_cpu_ptr(call->perf_events);
if (!perf_head || hlist_empty(perf_head))
return;
fields_size = get_field_size(event, var_ref_vals, var_ref_idx);
size = ALIGN(sizeof(*entry) + fields_size, 8);
entry = perf_trace_buf_alloc(size, &regs, &context);
if (unlikely(!entry))
return;
write_synth_entry(event, entry, var_ref_vals, var_ref_idx);
perf_fetch_caller_regs(regs);
perf_trace_buf_submit(entry, size, context,
call->event.type, 1, regs,
perf_head, NULL);
}
#endif
static void free_synth_event_print_fmt(struct trace_event_call *call)
{
if (call) {
@ -917,6 +981,9 @@ static int register_synth_event(struct synth_event *event)
call->flags = TRACE_EVENT_FL_TRACEPOINT;
call->class->reg = synth_event_reg;
call->class->probe = trace_event_raw_event_synth;
#ifdef CONFIG_PERF_EVENTS
call->class->perf_probe = perf_event_raw_event_synth;
#endif
call->data = event;
call->tp = event->tp;