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Commit 41d9c0be authored by Steven Rostedt (Red Hat)'s avatar Steven Rostedt (Red Hat) Committed by Steven Rostedt
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tracing: Always show all tracer options in the options directory 



There are options that are unique to a specific tracer (like function and
function graph). Currently, these options are only visible in the options
directory when the tracer is enabled.

This has been a pain, especially for something like the func_stack_trace
option that if used inappropriately, could bring the system to a crawl. But
the only way to see it, is to enable the function tracer.

For example, if one had done:

 # cd /sys/kernel/tracing
 # echo __schedule > set_ftrace_filter
 # echo 1 > options/func_stack_trace
 # echo function > current_tracer

The __schedule call will be traced and a stack trace will also be recorded
there. Now when you were done, you may do...

 # echo nop > current_tracer
 # echo > set_ftrace_filter

But you forgot to disable the func_stack_trace. The only way to disable it
is to re-enable function tracing first. If you do not add a filter to
set_ftrace_filter and just do:

 # echo function > current_tracer

Now you would be performing a stack trace on *every* function! On some
systems, that causes a live lock. Others may take a few minutes to fix your
mistake.

Having the func_stack_trace option visible allows you to check it and
disable it before enabling the funtion tracer.

Signed-off-by: default avatarSteven Rostedt <rostedt@goodmis.org>
parent 73dddbb5

kernel/trace/trace.c

+19 −34
Original line number Diff line number Diff line
@@ -1213,6 +1213,8 @@ static inline int run_tracer_selftest(struct tracer *type) 
}

#endif /* CONFIG_FTRACE_STARTUP_TEST */



static void add_tracer_options(struct trace_array *tr, struct tracer *t);



/**

 * register_tracer - register a tracer with the ftrace system.

 * @type - the plugin for the tracer
@@ -1262,6 +1264,7 @@ int register_tracer(struct tracer *type) 


	type->next = trace_types;

	trace_types = type;

	add_tracer_options(&global_trace, type);



 out:

	tracing_selftest_running = false;
@@ -4287,9 +4290,6 @@ struct trace_option_dentry; 
static struct trace_option_dentry *

create_trace_option_files(struct trace_array *tr, struct tracer *tracer);



static void

destroy_trace_option_files(struct trace_option_dentry *topts);



/*

 * Used to clear out the tracer before deletion of an instance.

 * Must have trace_types_lock held.
@@ -4307,10 +4307,8 @@ static void tracing_set_nop(struct trace_array *tr) 
	tr->current_trace = &nop_trace;

}



static void update_tracer_options(struct trace_array *tr, struct tracer *t)

static void add_tracer_options(struct trace_array *tr, struct tracer *t)

{

	static struct trace_option_dentry *topts;



	/* Only enable if the directory has been created already. */

	if (!tr->dir)

		return;
@@ -4319,8 +4317,11 @@ static void update_tracer_options(struct trace_array *tr, struct tracer *t) 
	if (!(tr->flags & TRACE_ARRAY_FL_GLOBAL))

		return;



	destroy_trace_option_files(topts);

	topts = create_trace_option_files(tr, t);

	/* Ignore if they were already created */

	if (t->topts)

		return;



	t->topts = create_trace_option_files(tr, t);

}



static int tracing_set_tracer(struct trace_array *tr, const char *buf)
@@ -4389,7 +4390,6 @@ static int tracing_set_tracer(struct trace_array *tr, const char *buf) 
		free_snapshot(tr);

	}

#endif

	update_tracer_options(tr, t);



#ifdef CONFIG_TRACER_MAX_TRACE

	if (t->use_max_tr && !had_max_tr) {
@@ -6119,13 +6119,6 @@ tracing_init_tracefs_percpu(struct trace_array *tr, long cpu) 
#include "trace_selftest.c"

#endif



struct trace_option_dentry {

	struct tracer_opt		*opt;

	struct tracer_flags		*flags;

	struct trace_array		*tr;

	struct dentry			*entry;

};



static ssize_t

trace_options_read(struct file *filp, char __user *ubuf, size_t cnt,

			loff_t *ppos)
@@ -6310,25 +6303,15 @@ create_trace_option_files(struct trace_array *tr, struct tracer *tracer) 
	if (!topts)

		return NULL;



	for (cnt = 0; opts[cnt].name; cnt++)

	for (cnt = 0; opts[cnt].name; cnt++) {

		create_trace_option_file(tr, &topts[cnt], flags,

					 &opts[cnt]);



	return topts;

		WARN_ONCE(topts[cnt].entry == NULL,

			  "Failed to create trace option: %s",

			  opts[cnt].name);

	}



static void

destroy_trace_option_files(struct trace_option_dentry *topts)

{

	int cnt;



	if (!topts)

		return;



	for (cnt = 0; topts[cnt].opt; cnt++)

		tracefs_remove(topts[cnt].entry);



	kfree(topts);

	return topts;

}



static struct dentry *
@@ -6812,6 +6795,7 @@ static struct notifier_block trace_module_nb = { 
static __init int tracer_init_tracefs(void)

{

	struct dentry *d_tracer;

	struct tracer *t;



	trace_access_lock_init();
@@ -6850,9 +6834,10 @@ static __init int tracer_init_tracefs(void) 


	create_trace_options_dir(&global_trace);



	/* If the tracer was started via cmdline, create options for it here */

	if (global_trace.current_trace != &nop_trace)

		update_tracer_options(&global_trace, global_trace.current_trace);

	mutex_lock(&trace_types_lock);

	for (t = trace_types; t; t = t->next)

		add_tracer_options(&global_trace, t);

	mutex_unlock(&trace_types_lock);



	return 0;

}

kernel/trace/trace.h

+8 −0
Original line number Diff line number Diff line
@@ -333,6 +333,13 @@ struct tracer_flags { 
#define TRACER_OPT(s, b)	.name = #s, .bit = b





struct trace_option_dentry {

	struct tracer_opt		*opt;

	struct tracer_flags		*flags;

	struct trace_array		*tr;

	struct dentry			*entry;

};



/**

 * struct tracer - a specific tracer and its callbacks to interact with tracefs

 * @name: the name chosen to select it on the available_tracers file
@@ -387,6 +394,7 @@ struct tracer { 
						u32 mask, int set);

	struct tracer		*next;

	struct tracer_flags	*flags;

	struct trace_option_dentry *topts;

	int			enabled;

	int			ref;

	bool			print_max;