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Subject[PATCH v4] trace: Move trace event enable from fs_initcall to core_initcall
Date
This patch splits trace event initialization in two stages:
* ftrace enable
* sysfs event entry creation

This allows to capture trace events from an earlier point
by using 'trace_event' kernel parameter and is important
to trace boot-up allocations.

Note that, in order to enable events at core_initcall,
it's necessary to move init_ftrace_syscalls() from
core_initcall to early_initcall.

Cc: Steven Rostedt <rostedt@goodmis.org>
Signed-off-by: Ezequiel Garcia <elezegarcia@gmail.com>
---
Changes from v1:
* Rework code as requested by Steven.

Changes from v2:
* Move init_ftrace_syscalls() to early_initcall,
so syscalls self-test pass.

Changes from v3:
* Fix issue reported by Steven:
event_trace_init() now iterates on added events (instead of full array).
This way we don't create an event dir for events that failed to enable.

kernel/trace/trace_events.c | 108 +++++++++++++++++++++++++++--------------
kernel/trace/trace_syscalls.c | 2 +-
2 files changed, 73 insertions(+), 37 deletions(-)

diff --git a/kernel/trace/trace_events.c b/kernel/trace/trace_events.c
index 29111da..437202d 100644
--- a/kernel/trace/trace_events.c
+++ b/kernel/trace/trace_events.c
@@ -1199,6 +1199,31 @@ event_create_dir(struct ftrace_event_call *call, struct dentry *d_events,
return 0;
}

+static void event_remove(struct ftrace_event_call *call)
+{
+ ftrace_event_enable_disable(call, 0);
+ if (call->event.funcs)
+ __unregister_ftrace_event(&call->event);
+ list_del(&call->list);
+}
+
+static int event_init(struct ftrace_event_call *call)
+{
+ int ret = 0;
+
+ if (WARN_ON(!call->name))
+ return -EINVAL;
+
+ if (call->class->raw_init) {
+ ret = call->class->raw_init(call);
+ if (ret < 0 && ret != -ENOSYS)
+ pr_warn("Could not initialize trace events/%s\n",
+ call->name);
+ }
+
+ return ret;
+}
+
static int
__trace_add_event_call(struct ftrace_event_call *call, struct module *mod,
const struct file_operations *id,
@@ -1209,19 +1234,9 @@ __trace_add_event_call(struct ftrace_event_call *call, struct module *mod,
struct dentry *d_events;
int ret;

- /* The linker may leave blanks */
- if (!call->name)
- return -EINVAL;
-
- if (call->class->raw_init) {
- ret = call->class->raw_init(call);
- if (ret < 0) {
- if (ret != -ENOSYS)
- pr_warning("Could not initialize trace events/%s\n",
- call->name);
- return ret;
- }
- }
+ ret = event_init(call);
+ if (ret < 0)
+ return ret;

d_events = event_trace_events_dir();
if (!d_events)
@@ -1272,13 +1287,10 @@ static void remove_subsystem_dir(const char *name)
*/
static void __trace_remove_event_call(struct ftrace_event_call *call)
{
- ftrace_event_enable_disable(call, 0);
- if (call->event.funcs)
- __unregister_ftrace_event(&call->event);
- debugfs_remove_recursive(call->dir);
- list_del(&call->list);
+ event_remove(call);
trace_destroy_fields(call);
destroy_preds(call);
+ debugfs_remove_recursive(call->dir);
remove_subsystem_dir(call->class->system);
}

@@ -1450,15 +1462,43 @@ static __init int setup_trace_event(char *str)
}
__setup("trace_event=", setup_trace_event);

+static __init int event_trace_enable(void)
+{
+ struct ftrace_event_call **iter, *call;
+ char *buf = bootup_event_buf;
+ char *token;
+ int ret;
+
+ for_each_event(iter, __start_ftrace_events, __stop_ftrace_events) {
+
+ call = *iter;
+ ret = event_init(call);
+ if (!ret)
+ list_add(&call->list, &ftrace_events);
+ }
+
+ while (true) {
+ token = strsep(&buf, ",");
+
+ if (!token)
+ break;
+ if (!*token)
+ continue;
+
+ ret = ftrace_set_clr_event(token, 1);
+ if (ret)
+ pr_warn("Failed to enable trace event: %s\n", token);
+ }
+ return 0;
+}
+
static __init int event_trace_init(void)
{
- struct ftrace_event_call **call;
+ struct ftrace_event_call *call;
struct dentry *d_tracer;
struct dentry *entry;
struct dentry *d_events;
int ret;
- char *buf = bootup_event_buf;
- char *token;

d_tracer = tracing_init_dentry();
if (!d_tracer)
@@ -1497,24 +1537,19 @@ static __init int event_trace_init(void)
if (trace_define_common_fields())
pr_warning("tracing: Failed to allocate common fields");

- for_each_event(call, __start_ftrace_events, __stop_ftrace_events) {
- __trace_add_event_call(*call, NULL, &ftrace_event_id_fops,
+ /*
+ * Early initialization already enabled ftrace event.
+ * Now it's only necessary to create the event directory.
+ */
+ list_for_each_entry(call, &ftrace_events, list) {
+
+ ret = event_create_dir(call, d_events,
+ &ftrace_event_id_fops,
&ftrace_enable_fops,
&ftrace_event_filter_fops,
&ftrace_event_format_fops);
- }
-
- while (true) {
- token = strsep(&buf, ",");
-
- if (!token)
- break;
- if (!*token)
- continue;
-
- ret = ftrace_set_clr_event(token, 1);
- if (ret)
- pr_warning("Failed to enable trace event: %s\n", token);
+ if (ret < 0)
+ event_remove(call);
}

ret = register_module_notifier(&trace_module_nb);
@@ -1523,6 +1558,7 @@ static __init int event_trace_init(void)

return 0;
}
+core_initcall(event_trace_enable);
fs_initcall(event_trace_init);

#ifdef CONFIG_FTRACE_STARTUP_TEST
diff --git a/kernel/trace/trace_syscalls.c b/kernel/trace/trace_syscalls.c
index 96fc733..07b4e5a 100644
--- a/kernel/trace/trace_syscalls.c
+++ b/kernel/trace/trace_syscalls.c
@@ -487,7 +487,7 @@ int __init init_ftrace_syscalls(void)

return 0;
}
-core_initcall(init_ftrace_syscalls);
+early_initcall(init_ftrace_syscalls);

#ifdef CONFIG_PERF_EVENTS

--
1.7.8.6


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