linux-kernel - [PATCH 4.14 19/22] tracing: Reverse the order of trace_types_lock and event

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Message-Id: <20200508123036.277013811@linuxfoundation.org>
Date:   Fri,  8 May 2020 14:35:31 +0200
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     linux-kernel@...r.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        stable@...r.kernel.org, Tom Zanussi <tom.zanussi@...ux.intel.com>,
        "Steven Rostedt (VMware)" <rostedt@...dmis.org>,
        =?UTF-8?q?Andress=20Kuo=20 ?= <Andress.Kuo@...iatek.com>
Subject: [PATCH 4.14 19/22] tracing: Reverse the order of trace_types_lock and event_mutex

From: Steven Rostedt (VMware) <rostedt@...dmis.org>

commit 12ecef0cb12102d8c034770173d2d1363cb97d52 upstream.

In order to make future changes where we need to call
tracing_set_clock() from within an event command, the order of
trace_types_lock and event_mutex must be reversed, as the event command
will hold event_mutex and the trace_types_lock is taken from within
tracing_set_clock().

Link: http://lkml.kernel.org/r/20170921162249.0dde3dca@gandalf.local.home

Requested-by: Tom Zanussi <tom.zanussi@...ux.intel.com>
Signed-off-by: Steven Rostedt (VMware) <rostedt@...dmis.org>
Cc: Andress Kuo (郭孟修) <Andress.Kuo@...iatek.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>

---
 kernel/trace/trace.c        |    5 +++++
 kernel/trace/trace_events.c |   31 +++++++++++++++----------------
 2 files changed, 20 insertions(+), 16 deletions(-)

--- a/kernel/trace/trace.c
+++ b/kernel/trace/trace.c
@@ -7720,6 +7720,7 @@ static int instance_mkdir(const char *na
 	struct trace_array *tr;
 	int ret;
 
+	mutex_lock(&event_mutex);
 	mutex_lock(&trace_types_lock);
 
 	ret = -EEXIST;
@@ -7775,6 +7776,7 @@ static int instance_mkdir(const char *na
 	list_add(&tr->list, &ftrace_trace_arrays);
 
 	mutex_unlock(&trace_types_lock);
+	mutex_unlock(&event_mutex);
 
 	return 0;
 
@@ -7786,6 +7788,7 @@ static int instance_mkdir(const char *na
 
  out_unlock:
 	mutex_unlock(&trace_types_lock);
+	mutex_unlock(&event_mutex);
 
 	return ret;
 
@@ -7798,6 +7801,7 @@ static int instance_rmdir(const char *na
 	int ret;
 	int i;
 
+	mutex_lock(&event_mutex);
 	mutex_lock(&trace_types_lock);
 
 	ret = -ENODEV;
@@ -7843,6 +7847,7 @@ static int instance_rmdir(const char *na
 
  out_unlock:
 	mutex_unlock(&trace_types_lock);
+	mutex_unlock(&event_mutex);
 
 	return ret;
 }
--- a/kernel/trace/trace_events.c
+++ b/kernel/trace/trace_events.c
@@ -1403,8 +1403,8 @@ static int subsystem_open(struct inode *
 		return -ENODEV;
 
 	/* Make sure the system still exists */
-	mutex_lock(&trace_types_lock);
 	mutex_lock(&event_mutex);
+	mutex_lock(&trace_types_lock);
 	list_for_each_entry(tr, &ftrace_trace_arrays, list) {
 		list_for_each_entry(dir, &tr->systems, list) {
 			if (dir == inode->i_private) {
@@ -1418,8 +1418,8 @@ static int subsystem_open(struct inode *
 		}
 	}
  exit_loop:
-	mutex_unlock(&event_mutex);
 	mutex_unlock(&trace_types_lock);
+	mutex_unlock(&event_mutex);
 
 	if (!system)
 		return -ENODEV;
@@ -2305,15 +2305,15 @@ static void __add_event_to_tracers(struc
 int trace_add_event_call(struct trace_event_call *call)
 {
 	int ret;
-	mutex_lock(&trace_types_lock);
 	mutex_lock(&event_mutex);
+	mutex_lock(&trace_types_lock);
 
 	ret = __register_event(call, NULL);
 	if (ret >= 0)
 		__add_event_to_tracers(call);
 
-	mutex_unlock(&event_mutex);
 	mutex_unlock(&trace_types_lock);
+	mutex_unlock(&event_mutex);
 	return ret;
 }
 
@@ -2367,13 +2367,13 @@ int trace_remove_event_call(struct trace
 {
 	int ret;
 
-	mutex_lock(&trace_types_lock);
 	mutex_lock(&event_mutex);
+	mutex_lock(&trace_types_lock);
 	down_write(&trace_event_sem);
 	ret = probe_remove_event_call(call);
 	up_write(&trace_event_sem);
-	mutex_unlock(&event_mutex);
 	mutex_unlock(&trace_types_lock);
+	mutex_unlock(&event_mutex);
 
 	return ret;
 }
@@ -2435,8 +2435,8 @@ static int trace_module_notify(struct no
 {
 	struct module *mod = data;
 
-	mutex_lock(&trace_types_lock);
 	mutex_lock(&event_mutex);
+	mutex_lock(&trace_types_lock);
 	switch (val) {
 	case MODULE_STATE_COMING:
 		trace_module_add_events(mod);
@@ -2445,8 +2445,8 @@ static int trace_module_notify(struct no
 		trace_module_remove_events(mod);
 		break;
 	}
-	mutex_unlock(&event_mutex);
 	mutex_unlock(&trace_types_lock);
+	mutex_unlock(&event_mutex);
 
 	return 0;
 }
@@ -2961,24 +2961,24 @@ create_event_toplevel_files(struct dentr
  * creates the event hierachry in the @parent/events directory.
  *
  * Returns 0 on success.
+ *
+ * Must be called with event_mutex held.
  */
 int event_trace_add_tracer(struct dentry *parent, struct trace_array *tr)
 {
 	int ret;
 
-	mutex_lock(&event_mutex);
+	lockdep_assert_held(&event_mutex);
 
 	ret = create_event_toplevel_files(parent, tr);
 	if (ret)
-		goto out_unlock;
+		goto out;
 
 	down_write(&trace_event_sem);
 	__trace_add_event_dirs(tr);
 	up_write(&trace_event_sem);
 
- out_unlock:
-	mutex_unlock(&event_mutex);
-
+ out:
 	return ret;
 }
 
@@ -3007,9 +3007,10 @@ early_event_add_tracer(struct dentry *pa
 	return ret;
 }
 
+/* Must be called with event_mutex held */
 int event_trace_del_tracer(struct trace_array *tr)
 {
-	mutex_lock(&event_mutex);
+	lockdep_assert_held(&event_mutex);
 
 	/* Disable any event triggers and associated soft-disabled events */
 	clear_event_triggers(tr);
@@ -3030,8 +3031,6 @@ int event_trace_del_tracer(struct trace_
 
 	tr->event_dir = NULL;
 
-	mutex_unlock(&event_mutex);
-
 	return 0;
 }