Commit 3fe3d619 authored by Oleg Nesterov's avatar Oleg Nesterov Committed by Steven Rostedt
Browse files

tracing/kprobes: Kill probe_enable_lock 

enable_trace_probe() and disable_trace_probe() should not worry about
serialization, the caller (perf_trace_init or __ftrace_set_clr_event)
holds event_mutex.

They are also called by kprobe_trace_self_tests_init(), but this __init
function can't race with itself or trace_events.c

And note that this code depended on event_mutex even before 41a7dd42
which introduced probe_enable_lock. In fact it assumes that the caller
kprobe_register() can never race with itself. Otherwise, say, tp->flags
manipulations are racy.

Link: http://lkml.kernel.org/r/20130620173809.GA13158@redhat.com



Acked-by: default avatarMasami Hiramatsu <masami.hiramatsu.pt@hitachi.com>
Signed-off-by: default avatarOleg Nesterov <oleg@redhat.com>
Signed-off-by: default avatarSteven Rostedt <rostedt@goodmis.org>
parent 288e984e

kernel/trace/trace_kprobe.c

+20 −23
Original line number Diff line number Diff line
@@ -183,16 +183,15 @@ static struct trace_probe *find_trace_probe(const char *event, 
	return NULL;

}



/*

 * This and enable_trace_probe/disable_trace_probe rely on event_mutex

 * held by the caller, __ftrace_set_clr_event().

 */

static int trace_probe_nr_files(struct trace_probe *tp)

{

	struct ftrace_event_file **file;

	struct ftrace_event_file **file = rcu_dereference_raw(tp->files);

	int ret = 0;



	/*

	 * Since all tp->files updater is protected by probe_enable_lock,

	 * we don't need to lock an rcu_read_lock.

	 */

	file = rcu_dereference_raw(tp->files);

	if (file)

		while (*(file++))

			ret++;
@@ -200,8 +199,6 @@ static int trace_probe_nr_files(struct trace_probe *tp) 
	return ret;

}



static DEFINE_MUTEX(probe_enable_lock);



/*

 * Enable trace_probe

 * if the file is NULL, enable "perf" handler, or enable "trace" handler.
@@ -211,8 +208,6 @@ enable_trace_probe(struct trace_probe *tp, struct ftrace_event_file *file) 
{

	int ret = 0;



	mutex_lock(&probe_enable_lock);



	if (file) {

		struct ftrace_event_file **new, **old;

		int n = trace_probe_nr_files(tp);
@@ -223,7 +218,7 @@ enable_trace_probe(struct trace_probe *tp, struct ftrace_event_file *file) 
			      GFP_KERNEL);

		if (!new) {

			ret = -ENOMEM;

			goto out_unlock;

			goto out;

		}

		memcpy(new, old, n * sizeof(struct ftrace_event_file *));

		new[n] = file;
@@ -246,10 +241,7 @@ enable_trace_probe(struct trace_probe *tp, struct ftrace_event_file *file) 
		else

			ret = enable_kprobe(&tp->rp.kp);

	}



 out_unlock:

	mutex_unlock(&probe_enable_lock);



 out:

	return ret;

}
@@ -282,8 +274,6 @@ disable_trace_probe(struct trace_probe *tp, struct ftrace_event_file *file) 
{

	int ret = 0;



	mutex_lock(&probe_enable_lock);



	if (file) {

		struct ftrace_event_file **new, **old;

		int n = trace_probe_nr_files(tp);
@@ -292,7 +282,7 @@ disable_trace_probe(struct trace_probe *tp, struct ftrace_event_file *file) 
		old = rcu_dereference_raw(tp->files);

		if (n == 0 || trace_probe_file_index(tp, file) < 0) {

			ret = -EINVAL;

			goto out_unlock;

			goto out;

		}



		if (n == 1) {	/* Remove the last file */
@@ -303,7 +293,7 @@ disable_trace_probe(struct trace_probe *tp, struct ftrace_event_file *file) 
				      GFP_KERNEL);

			if (!new) {

				ret = -ENOMEM;

				goto out_unlock;

				goto out;

			}



			/* This copy & check loop copies the NULL stopper too */
@@ -326,10 +316,7 @@ disable_trace_probe(struct trace_probe *tp, struct ftrace_event_file *file) 
		else

			disable_kprobe(&tp->rp.kp);

	}



 out_unlock:

	mutex_unlock(&probe_enable_lock);



 out:

	return ret;

}
@@ -1214,6 +1201,12 @@ kretprobe_perf_func(struct trace_probe *tp, struct kretprobe_instance *ri, 
}

#endif	/* CONFIG_PERF_EVENTS */



/*

 * called by perf_trace_init() or __ftrace_set_clr_event() under event_mutex.

 *

 * kprobe_trace_self_tests_init() does enable_trace_probe/disable_trace_probe

 * lockless, but we can't race with this __init function.

 */

static __kprobes

int kprobe_register(struct ftrace_event_call *event,

		    enum trace_reg type, void *data)
@@ -1379,6 +1372,10 @@ find_trace_probe_file(struct trace_probe *tp, struct trace_array *tr) 
	return NULL;

}



/*

 * Nobody but us can call enable_trace_probe/disable_trace_probe at this

 * stage, we can do this lockless.

 */

static __init int kprobe_trace_self_tests_init(void)

{

	int ret, warn = 0;

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