[PATCH] tracing: fix wrong output of the __array field type string

["zhangwei(Jovi)" <jovi.zhangwei@huawei.com>]

 A bug was found in events/sched/sched_switch/format.

	field:char prev_comm[32];       offset:8;       size:16;        signed:1;

and prev_comm field is defined as:

	__array(        char,   prev_comm,      TASK_COMM_LEN   )

Note TASK_COMM_LEN is 16, but the arrary len is 32 in there.

The root cause is we use global temp buffer event_storage as
constant type string in trace_define_field function when
define __array field, this will make old field type string
flushed by new string in event_storage.

In this patch, type string is checked by core_kernel_data firstly,
if it's not core kernel data, then copy the storage.

This patch also kill the global storage event_storage.

events/sched/sched_switch/format changed after patch:

	field:char prev_comm[16];       offset:8;       size:16;        signed:1;

Signed-off-by: zhangwei(Jovi) <jovi.zhangwei@huawei.com>
---
 include/linux/ftrace_event.h |    2 --
 include/trace/ftrace.h       |    4 ++--
 kernel/trace/trace_events.c  |   20 +++++++++++++-------
 kernel/trace/trace_export.c  |    4 ++--
 4 files changed, 17 insertions(+), 13 deletions(-)

diff --git a/include/linux/ftrace_event.h b/include/linux/ftrace_event.h
index 4372658..bd91f0e 100644
--- a/include/linux/ftrace_event.h
+++ b/include/linux/ftrace_event.h
@@ -324,8 +324,6 @@ enum {
 };

 #define EVENT_STORAGE_SIZE 128
-extern struct mutex event_storage_mutex;
-extern char event_storage[EVENT_STORAGE_SIZE];

 extern int trace_event_raw_init(struct ftrace_event_call *call);
 extern int trace_define_field(struct ftrace_event_call *call, const char *type,
diff --git a/include/trace/ftrace.h b/include/trace/ftrace.h
index d615f78..c8bd295 100644
--- a/include/trace/ftrace.h
+++ b/include/trace/ftrace.h
@@ -303,7 +303,8 @@ static struct trace_event_functions ftrace_event_type_funcs_##call = {	\
 #undef __array
 #define __array(type, item, len)					\
 	do {								\
-		mutex_lock(&event_storage_mutex);			\
+		char event_storage[EVENT_STORAGE_SIZE];			\
+									\
 		BUILD_BUG_ON(len > MAX_FILTER_STR_VAL);			\
 		snprintf(event_storage, sizeof(event_storage),		\
 			 "%s[%d]", #type, len);				\
@@ -311,7 +312,6 @@ static struct trace_event_functions ftrace_event_type_funcs_##call = {	\
 				 offsetof(typeof(field), item),		\
 				 sizeof(field.item),			\
 				 is_signed_type(type), FILTER_OTHER);	\
-		mutex_unlock(&event_storage_mutex);			\
 		if (ret)						\
 			return ret;					\
 	} while (0);
diff --git a/kernel/trace/trace_events.c b/kernel/trace/trace_events.c
index 5f694ce..5827287 100644
--- a/kernel/trace/trace_events.c
+++ b/kernel/trace/trace_events.c
@@ -27,12 +27,6 @@

 DEFINE_MUTEX(event_mutex);

-DEFINE_MUTEX(event_storage_mutex);
-EXPORT_SYMBOL_GPL(event_storage_mutex);
-
-char event_storage[EVENT_STORAGE_SIZE];
-EXPORT_SYMBOL_GPL(event_storage);
-
 LIST_HEAD(ftrace_events);
 static LIST_HEAD(ftrace_common_fields);

@@ -100,7 +94,15 @@ static int __trace_define_field(struct list_head *head, const char *type,
 		goto err;

 	field->name = name;
-	field->type = type;
+
+	/* for __array field, type is not a constant string */
+	if (!core_kernel_data((unsigned long)type)) {
+		field->type = kstrdup(type, GFP_KERNEL);
+		if (!field->type)
+			goto err;
+	} else {
+		field->type = type;
+	}

 	if (filter_type == FILTER_OTHER)
 		field->filter_type = filter_assign_type(type);
@@ -166,6 +168,10 @@ static void trace_destroy_fields(struct ftrace_event_call *call)
 	head = trace_get_fields(call);
 	list_for_each_entry_safe(field, next, head, link) {
 		list_del(&field->link);
+
+		if (!core_kernel_data((unsigned long)field->type))
+			kfree(field->type);
+
 		kmem_cache_free(field_cachep, field);
 	}
 }
diff --git a/kernel/trace/trace_export.c b/kernel/trace/trace_export.c
index d21a746..490eb32 100644
--- a/kernel/trace/trace_export.c
+++ b/kernel/trace/trace_export.c
@@ -95,15 +95,15 @@ static void __always_unused ____ftrace_check_##name(void)		\
 #undef __array
 #define __array(type, item, len)					\
 	do {								\
+		char event_storage[EVENT_STORAGE_SIZE];			\
+									\
 		BUILD_BUG_ON(len > MAX_FILTER_STR_VAL);			\
-		mutex_lock(&event_storage_mutex);			\
 		snprintf(event_storage, sizeof(event_storage),		\
 			 "%s[%d]", #type, len);				\
 		ret = trace_define_field(event_call, event_storage, #item, \
 				 offsetof(typeof(field), item),		\
 				 sizeof(field.item),			\
 				 is_signed_type(type), filter_type);	\
-		mutex_unlock(&event_storage_mutex);			\
 		if (ret)						\
 			return ret;					\
 	} while (0);
-- 
1.7.9.7