Commit 7904b5c4 authored by Steven Rostedt (Red Hat)'s avatar Steven Rostedt (Red Hat) Committed by Steven Rostedt
Browse files

tracepoint: Give priority to probes of tracepoints 



In order to guarantee that a probe will be called before other probes that
are attached to a tracepoint, there needs to be a mechanism to provide
priority of one probe over the others.

Adding a prio field to the struct tracepoint_func, which lets the probes be
sorted by the priority set in the structure. If no priority is specified,
then a priority of 10 is given (this is a macro, and perhaps may be changed
in the future).

Now probes may be added to affect other probes that are attached to a
tracepoint with a guaranteed order.

One use case would be to allow tracing of tracepoints be able to filter by
pid. A special (higher priority probe) may be added to the sched_switch
tracepoint and set the necessary flags of the other tracepoints to notify
them if they should be traced or not. In case a tracepoint is enabled at the
sched_switch tracepoint too, the order of the two are not random.

Cc: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Signed-off-by: default avatarSteven Rostedt <rostedt@goodmis.org>
parent 883a1e86

include/linux/tracepoint.h

+13 −0
Original line number Diff line number Diff line
@@ -26,6 +26,7 @@ struct notifier_block; 
struct tracepoint_func {

	void *func;

	void *data;

	int prio;

};



struct tracepoint {
@@ -42,9 +43,14 @@ struct trace_enum_map { 
	unsigned long		enum_value;

};



#define TRACEPOINT_DEFAULT_PRIO	10



extern int

tracepoint_probe_register(struct tracepoint *tp, void *probe, void *data);

extern int

tracepoint_probe_register_prio(struct tracepoint *tp, void *probe, void *data,

			       int prio);

extern int

tracepoint_probe_unregister(struct tracepoint *tp, void *probe, void *data);

extern void

for_each_kernel_tracepoint(void (*fct)(struct tracepoint *tp, void *priv),
@@ -207,6 +213,13 @@ extern void syscall_unregfunc(void); 
						(void *)probe, data);	\

	}								\

	static inline int						\

	register_trace_prio_##name(void (*probe)(data_proto), void *data,\

				   int prio)				\

	{								\

		return tracepoint_probe_register_prio(&__tracepoint_##name, \

					      (void *)probe, data, prio); \

	}								\

	static inline int						\

	unregister_trace_##name(void (*probe)(data_proto), void *data)	\

	{								\

		return tracepoint_probe_unregister(&__tracepoint_##name,\

kernel/tracepoint.c

+50 −11
Original line number Diff line number Diff line
@@ -91,11 +91,13 @@ static void debug_print_probes(struct tracepoint_func *funcs) 
		printk(KERN_DEBUG "Probe %d : %p\n", i, funcs[i].func);

}



static struct tracepoint_func *func_add(struct tracepoint_func **funcs,

		struct tracepoint_func *tp_func)

static struct tracepoint_func *

func_add(struct tracepoint_func **funcs, struct tracepoint_func *tp_func,

	 int prio)

{

	int nr_probes = 0;

	struct tracepoint_func *old, *new;

	int nr_probes = 0;

	int pos = -1;



	if (WARN_ON(!tp_func->func))

		return ERR_PTR(-EINVAL);
@@ -104,18 +106,33 @@ static struct tracepoint_func *func_add(struct tracepoint_func **funcs, 
	old = *funcs;

	if (old) {

		/* (N -> N+1), (N != 0, 1) probes */

		for (nr_probes = 0; old[nr_probes].func; nr_probes++)

		for (nr_probes = 0; old[nr_probes].func; nr_probes++) {

			/* Insert before probes of lower priority */

			if (pos < 0 && old[nr_probes].prio < prio)

				pos = nr_probes;

			if (old[nr_probes].func == tp_func->func &&

			    old[nr_probes].data == tp_func->data)

				return ERR_PTR(-EEXIST);

		}

	}

	/* + 2 : one for new probe, one for NULL func */

	new = allocate_probes(nr_probes + 2);

	if (new == NULL)

		return ERR_PTR(-ENOMEM);

	if (old)

	if (old) {

		if (pos < 0) {

			pos = nr_probes;

			memcpy(new, old, nr_probes * sizeof(struct tracepoint_func));

	new[nr_probes] = *tp_func;

		} else {

			/* Copy higher priority probes ahead of the new probe */

			memcpy(new, old, pos * sizeof(struct tracepoint_func));

			/* Copy the rest after it. */

			memcpy(new + pos + 1, old + pos,

			       (nr_probes - pos) * sizeof(struct tracepoint_func));

		}

	} else

		pos = 0;

	new[pos] = *tp_func;

	new[nr_probes + 1].func = NULL;

	*funcs = new;

	debug_print_probes(*funcs);
@@ -174,7 +191,7 @@ static void *func_remove(struct tracepoint_func **funcs, 
 * Add the probe function to a tracepoint.

 */

static int tracepoint_add_func(struct tracepoint *tp,

		struct tracepoint_func *func)

			       struct tracepoint_func *func, int prio)

{

	struct tracepoint_func *old, *tp_funcs;
@@ -183,7 +200,7 @@ static int tracepoint_add_func(struct tracepoint *tp, 


	tp_funcs = rcu_dereference_protected(tp->funcs,

			lockdep_is_held(&tracepoints_mutex));

	old = func_add(&tp_funcs, func);

	old = func_add(&tp_funcs, func, prio);

	if (IS_ERR(old)) {

		WARN_ON_ONCE(1);

		return PTR_ERR(old);
@@ -240,6 +257,7 @@ static int tracepoint_remove_func(struct tracepoint *tp, 
 * @tp: tracepoint

 * @probe: probe handler

 * @data: tracepoint data

 * @prio: priority of this function over other registered functions

 *

 * Returns 0 if ok, error value on error.

 * Note: if @tp is within a module, the caller is responsible for
@@ -247,7 +265,8 @@ static int tracepoint_remove_func(struct tracepoint *tp, 
 * performed either with a tracepoint module going notifier, or from

 * within module exit functions.

 */

int tracepoint_probe_register(struct tracepoint *tp, void *probe, void *data)

int tracepoint_probe_register_prio(struct tracepoint *tp, void *probe,

				   void *data, int prio)

{

	struct tracepoint_func tp_func;

	int ret;
@@ -255,10 +274,30 @@ int tracepoint_probe_register(struct tracepoint *tp, void *probe, void *data) 
	mutex_lock(&tracepoints_mutex);

	tp_func.func = probe;

	tp_func.data = data;

	ret = tracepoint_add_func(tp, &tp_func);

	tp_func.prio = prio;

	ret = tracepoint_add_func(tp, &tp_func, prio);

	mutex_unlock(&tracepoints_mutex);

	return ret;

}

EXPORT_SYMBOL_GPL(tracepoint_probe_register_prio);



/**

 * tracepoint_probe_register -  Connect a probe to a tracepoint

 * @tp: tracepoint

 * @probe: probe handler

 * @data: tracepoint data

 * @prio: priority of this function over other registered functions

 *

 * Returns 0 if ok, error value on error.

 * Note: if @tp is within a module, the caller is responsible for

 * unregistering the probe before the module is gone. This can be

 * performed either with a tracepoint module going notifier, or from

 * within module exit functions.

 */

int tracepoint_probe_register(struct tracepoint *tp, void *probe, void *data)

{

	return tracepoint_probe_register_prio(tp, probe, data, TRACEPOINT_DEFAULT_PRIO);

}

EXPORT_SYMBOL_GPL(tracepoint_probe_register);



/**

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