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Subject[for-next][PATCH 03/16] tracing: Reverse the order of trace_types_lock and event_mutex
From: "Steven Rostedt (VMware)" <rostedt@goodmis.org>

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@linux.intel.com>
Signed-off-by: Steven Rostedt (VMware) <rostedt@goodmis.org>
---
kernel/trace/trace.c | 5 +++++
kernel/trace/trace_events.c | 31 +++++++++++++++----------------
2 files changed, 20 insertions(+), 16 deletions(-)

diff --git a/kernel/trace/trace.c b/kernel/trace/trace.c
index 752e5daf0896..5f1ac7d3402c 100644
--- a/kernel/trace/trace.c
+++ b/kernel/trace/trace.c
@@ -7687,6 +7687,7 @@ static int instance_mkdir(const char *name)
struct trace_array *tr;
int ret;

+ mutex_lock(&event_mutex);
mutex_lock(&trace_types_lock);

ret = -EEXIST;
@@ -7742,6 +7743,7 @@ static int instance_mkdir(const char *name)
list_add(&tr->list, &ftrace_trace_arrays);

mutex_unlock(&trace_types_lock);
+ mutex_unlock(&event_mutex);

return 0;

@@ -7753,6 +7755,7 @@ static int instance_mkdir(const char *name)

out_unlock:
mutex_unlock(&trace_types_lock);
+ mutex_unlock(&event_mutex);

return ret;

@@ -7765,6 +7768,7 @@ static int instance_rmdir(const char *name)
int ret;
int i;

+ mutex_lock(&event_mutex);
mutex_lock(&trace_types_lock);

ret = -ENODEV;
@@ -7810,6 +7814,7 @@ static int instance_rmdir(const char *name)

out_unlock:
mutex_unlock(&trace_types_lock);
+ mutex_unlock(&event_mutex);

return ret;
}
diff --git a/kernel/trace/trace_events.c b/kernel/trace/trace_events.c
index 87468398b9ed..ec0f9aa4e151 100644
--- a/kernel/trace/trace_events.c
+++ b/kernel/trace/trace_events.c
@@ -1406,8 +1406,8 @@ static int subsystem_open(struct inode *inode, struct file *filp)
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) {
@@ -1421,8 +1421,8 @@ static int subsystem_open(struct inode *inode, struct file *filp)
}
}
exit_loop:
- mutex_unlock(&event_mutex);
mutex_unlock(&trace_types_lock);
+ mutex_unlock(&event_mutex);

if (!system)
return -ENODEV;
@@ -2294,15 +2294,15 @@ static void __add_event_to_tracers(struct trace_event_call *call);
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;
}

@@ -2356,13 +2356,13 @@ int trace_remove_event_call(struct trace_event_call *call)
{
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;
}
@@ -2424,8 +2424,8 @@ static int trace_module_notify(struct notifier_block *self,
{
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);
@@ -2434,8 +2434,8 @@ static int trace_module_notify(struct notifier_block *self,
trace_module_remove_events(mod);
break;
}
- mutex_unlock(&event_mutex);
mutex_unlock(&trace_types_lock);
+ mutex_unlock(&event_mutex);

return 0;
}
@@ -2950,24 +2950,24 @@ create_event_toplevel_files(struct dentry *parent, struct trace_array *tr)
* 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;
}

@@ -2996,9 +2996,10 @@ early_event_add_tracer(struct dentry *parent, struct trace_array *tr)
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);
@@ -3019,8 +3020,6 @@ int event_trace_del_tracer(struct trace_array *tr)

tr->event_dir = NULL;

- mutex_unlock(&event_mutex);
-
return 0;
}

--
2.13.2

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