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Date: Tue, 11 Sep 2012 20:34:30 -0400
From: Steven Rostedt <rostedt@...dmis.org>
To: Ezequiel Garcia <elezegarcia@...il.com>
Cc: linux-kernel@...r.kernel.org, Pekka Enberg <penberg@...nel.org>,
tim.bird@...sony.com, Ingo Molnar <mingo@...hat.com>
Subject: Re: [PATCH v3] trace: Move trace event enable from fs_initcall to
core_initcall
On Sat, 2012-09-08 at 17:01 -0300, Ezequiel Garcia wrote:
> 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.
Found another issue...
>
> Cc: Steven Rostedt <rostedt@...dmis.org>
> Signed-off-by: Ezequiel Garcia <elezegarcia@...il.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.
>
> kernel/trace/trace_events.c | 104 +++++++++++++++++++++++++++-------------
> kernel/trace/trace_syscalls.c | 2 +-
> 2 files changed, 71 insertions(+), 35 deletions(-)
>
> diff --git a/kernel/trace/trace_events.c b/kernel/trace/trace_events.c
> index 29111da..4eaf86e 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 raw_init() returns a failure, we skip this event.
> + 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);
> }
>
> @@ -1450,6 +1462,36 @@ 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;
> @@ -1457,8 +1499,6 @@ static __init int event_trace_init(void)
> 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");
>
> + /*
> + * Early initialization already enabled ftrace event.
> + * Now it's only necessary to create the event directory.
> + */
> for_each_event(call, __start_ftrace_events, __stop_ftrace_events) {
> - __trace_add_event_call(*call, NULL, &ftrace_event_id_fops,
Here, __trace_add_event_call() did the checks and did not create a
directory on raw_init() failure. But now there's no check, and we are
having events being created that should not be.
> +
> + ret = event_create_dir(*call, d_events,
> + &ftrace_event_id_fops,
> &ftrace_enable_fops,
> &ftrace_event_filter_fops,
> &ftrace_event_format_fops);
I found this out when there was errors in trace-cmd reading format
files. Looking into it, I found several syscalls that are not mapped to
a syscall_nr being created.
One solution would be to add another flag to the ftrace_event_call
structure, that notes the event has failed to initialize. Or better yet,
add a flag that just says that it was initialized. Then here we can skip
those events that do not have that flag set.
-- Steve
> - }
> -
> - 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
>
--
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