[PATCH] tracing/boot: Initialize per-instance event list in early boot

Masami Hiramatsu
2020-09-24T16:40:15Z

Initialize per-instance event list in early boot time (before
initializing instance directory on tracefs). This fixes boot-time
tracing to correctly handle the boot-time per-instance settings.

Signed-off-by: Masami Hiramatsu <mhiramat@kernel.org>
---
kernel/trace/trace.c | 3 ++-
kernel/trace/trace.h | 1 +
kernel/trace/trace_events.c | 30 ++++++++++++++++--------------
3 files changed, 19 insertions(+), 15 deletions(-)

diff --git a/kernel/trace/trace.c b/kernel/trace/trace.c
index f7696db52e7d..400ed1ec3b64 100644
--- a/kernel/trace/trace.c
+++ b/kernel/trace/trace.c
@@ -8700,7 +8700,8 @@ static struct trace_array *trace_array_create(const char *name)
ret = trace_array_create_dir(tr);
if (ret)
goto out_free_tr;
- }
+ } else
+ __trace_early_add_events(tr);

list_add(&tr->list, &ftrace_trace_arrays);

diff --git a/kernel/trace/trace.h b/kernel/trace/trace.h
index e1b3061ce06d..5b887cfbe5ec 100644
--- a/kernel/trace/trace.h
+++ b/kernel/trace/trace.h
@@ -1658,6 +1658,7 @@ extern void trace_event_enable_tgid_record(bool enable);
extern int event_trace_init(void);
extern int event_trace_add_tracer(struct dentry *parent, struct trace_array *tr);
extern int event_trace_del_tracer(struct trace_array *tr);
+extern void __trace_early_add_events(struct trace_array *tr);

extern struct trace_event_file *__find_event_file(struct trace_array *tr,
const char *system,
diff --git a/kernel/trace/trace_events.c b/kernel/trace/trace_events.c
index 720b0d72ea52..8ce334297bf3 100644
--- a/kernel/trace/trace_events.c
+++ b/kernel/trace/trace_events.c
@@ -3131,14 +3131,13 @@ static inline int register_event_cmds(void) { return 0; }
#endif /* CONFIG_DYNAMIC_FTRACE */

/*
- * The top level array has already had its trace_event_file
- * descriptors created in order to allow for early events to
- * be recorded. This function is called after the tracefs has been
- * initialized, and we now have to create the files associated
- * to the events.
+ * The top level array and trace arrays created by boot-time tracing
+ * have already had its trace_event_file descriptors created in order
+ * to allow for early events to be recorded.
+ * This function is called after the tracefs has been initialized,
+ * and we now have to create the files associated to the events.
*/
-static __init void
-__trace_early_add_event_dirs(struct trace_array *tr)
+static void __trace_early_add_event_dirs(struct trace_array *tr)
{
struct trace_event_file *file;
int ret;
@@ -3153,13 +3152,12 @@ __trace_early_add_event_dirs(struct trace_array *tr)
}

/*
- * For early boot up, the top trace array requires to have
- * a list of events that can be enabled. This must be done before
- * the filesystem is set up in order to allow events to be traced
- * early.
+ * For early boot up, the top trace array and the trace arrays created
+ * by boot-time tracing require to have a list of events that can be
+ * enabled. This must be done before the filesystem is set up in order
+ * to allow events to be traced early.
*/
-static __init void
-__trace_early_add_events(struct trace_array *tr)
+void __trace_early_add_events(struct trace_array *tr)
{
struct trace_event_call *call;
int ret;
@@ -3290,7 +3288,11 @@ int event_trace_add_tracer(struct dentry *parent, struct trace_array *tr)
goto out;

down_write(&trace_event_sem);
- __trace_add_event_dirs(tr);
+ /* If tr already has the event list, it is initialized in early boot. */
+ if (unlikely(!list_empty(&tr->events)))
+ __trace_early_add_event_dirs(tr);
+ else
+ __trace_add_event_dirs(tr);
up_write(&trace_event_sem);