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SubjectRe: [PATCH v2] tracing: Ignore mmiotrace from kernel commandline
On Wed, 30 Aug 2017 12:19:30 +0800
"Ziqian SUN (Zamir)" <zsun@redhat.com> wrote:

> From: "Ziqian SUN (Zamir)" <zsun@redhat.com>
>
> The mmiotrace tracer cannot be enabled with ftrace=mmiotrace in
> kernel commandline. With this patch, a trace_noboot_tracer_list
> is implemented and will be checked during system boot. If the
> tracer declares itself as not for boot up, system will print out
> a message and continue booting.
>
> Link: https://bugzilla.kernel.org/show_bug.cgi?id=196557
> Signed-off-by: Ziqian SUN (Zamir) <zsun@redhat.com>
> ---
> kernel/trace/trace.c | 34 +++++++++++++++++++++++++++++++++-
> kernel/trace/trace.h | 11 +++++++++++
> kernel/trace/trace_mmiotrace.c | 4 ++++
> 3 files changed, 48 insertions(+), 1 deletion(-)
>
> diff --git a/kernel/trace/trace.c b/kernel/trace/trace.c
> index 44004d8..0d25b1e 100644
> --- a/kernel/trace/trace.c
> +++ b/kernel/trace/trace.c
> @@ -319,6 +319,33 @@ void trace_free_pid_list(struct trace_pid_list *pid_list)
> kfree(pid_list);
> }
>
> +struct mutex trace_noboot_tracer_lock;
> +
> +DEFINE_MUTEX(trace_noboot_tracer_lock);
> +LIST_HEAD(trace_noboot_tracer_list);
> +
> +void trace_noboot_tracer_put(struct tracer_noboot *noboot_tracer)
> +{
> + mutex_lock(&trace_noboot_tracer_lock);
> + list_add(&noboot_tracer->list, &trace_noboot_tracer_list);
> + mutex_unlock(&trace_noboot_tracer_lock);
> +}
> +
> +bool trace_noboot_tracer_find(const char *str)
> +{
> + mutex_lock(&trace_noboot_tracer_lock);
> + struct tracer_noboot *ptr = NULL;
> +
> + list_for_each_entry(ptr, &trace_noboot_tracer_list, list) {
> + if (strcmp(ptr->name, str) == 0) {
> + mutex_unlock(&trace_noboot_tracer_lock);
> + return true;
> + }
> + }
> + mutex_unlock(&trace_noboot_tracer_lock);
> + return false;
> +}
> +
> /**
> * trace_find_filtered_pid - check if a pid exists in a filtered_pid list
> * @filtered_pids: The list of pids to check
> @@ -1641,8 +1668,13 @@ int __init register_tracer(struct tracer *type)
> if (strncmp(default_bootup_tracer, type->name, MAX_TRACER_SIZE))
> goto out_unlock;
>
> + /* If the tracer should not be enabled by kernel parameter */
> + if (trace_noboot_tracer_find(type->name)) {
> + pr_warn("Tracer '%s' cannot be enabled during boot\n", type->name);
> + goto out_unlock;
> + }
> +
> printk(KERN_INFO "Starting tracer '%s'\n", type->name);
> - /* Do we want this tracer to start on bootup? */
> tracing_set_tracer(&global_trace, type->name);
> default_bootup_tracer = NULL;
>
> diff --git a/kernel/trace/trace.h b/kernel/trace/trace.h
> index 490ba22..23bc668 100644
> --- a/kernel/trace/trace.h
> +++ b/kernel/trace/trace.h
> @@ -502,6 +502,17 @@ enum {
> TRACE_IRQ_BIT,
> };
>
> +/*
> + * For tracer that cannot be enabled during boot time.
> + */
> +
> +struct tracer_noboot {
> + const char *name;
> + struct list_head list;
> +};
> +
> +void trace_noboot_tracer_put(struct tracer_noboot *noboot_tracer);
> +
> #define trace_recursion_set(bit) do { (current)->trace_recursion |= (1<<(bit)); } while (0)
> #define trace_recursion_clear(bit) do { (current)->trace_recursion &= ~(1<<(bit)); } while (0)
> #define trace_recursion_test(bit) ((current)->trace_recursion & (1<<(bit)))
> diff --git a/kernel/trace/trace_mmiotrace.c b/kernel/trace/trace_mmiotrace.c
> index cd7480d..06aa0a5 100644
> --- a/kernel/trace/trace_mmiotrace.c
> +++ b/kernel/trace/trace_mmiotrace.c
> @@ -286,6 +286,10 @@ static enum print_line_t mmio_print_line(struct trace_iterator *iter)
>
> __init static int init_mmio_trace(void)
> {
> + struct tracer_noboot mmio_notrace;
> +
> + mmio_notrace.name = "mmiotrace";
> + trace_noboot_tracer_put(&mmio_notrace);
> return register_tracer(&mmio_tracer);
> }
> device_initcall(init_mmio_trace);

This is way overkill. Just add

bool noboot;

to struct tracer in trace.h and then to the mmiotracer:

struct tracer mmio_tracer = {
[..]
.noboot = true,
};


And then in tracing_set_tracer() add after:

if (t == tr->current_trace)
goto out;

this:

if (system_state < SYSTEM_RUNNING && t->noboot) {
WARN(1, "Tracer %s not allowed on command line",
t->name);
goto out;
}

That's it. No need for locking or anything else.

-- Steve



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