tracing: Fix array size mismatch in format string

In event format strings, the array size is reported in two locations.
One in array subscript and then via the "size:" attribute. The values
reported there have a mismatch.

For e.g., in sched:sched_switch the prev_comm and next_comm character
arrays have subscript values as [32] where as the actual field size is
16.

name: sched_switch
ID: 301
format:
        field:unsigned short common_type;       offset:0;       size:2; signed:0;
        field:unsigned char common_flags;       offset:2;       size:1; signed:0;
        field:unsigned char common_preempt_count;       offset:3;       size:1;signed:0;
        field:int common_pid;   offset:4;       size:4; signed:1;

        field:char prev_comm[32];       offset:8;       size:16;        signed:1;
        field:pid_t prev_pid;   offset:24;      size:4; signed:1;
        field:int prev_prio;    offset:28;      size:4; signed:1;
        field:long prev_state;  offset:32;      size:8; signed:1;
        field:char next_comm[32];       offset:40;      size:16;        signed:1;
        field:pid_t next_pid;   offset:56;      size:4; signed:1;
        field:int next_prio;    offset:60;      size:4; signed:1;

After bisection, the following commit was blamed:
92edca0 tracing: Use direct field, type and system names

This commit removes the duplication of strings for field->name and
field->type assuming that all the strings passed in
__trace_define_field() are immutable. This is not true for arrays, where
the type string is created in event_storage variable and field->type for
all array fields points to event_storage.

Use __stringify() to create a string constant for the type string.

Also, get rid of event_storage and event_storage_mutex that are not
needed anymore.

also, an added benefit is that this reduces the overhead of events a bit more:

   text    data     bss     dec     hex filename
8424787 2036472 1302528 11763787         b3804b vmlinux
8420814 2036408 1302528 11759750         b37086 vmlinux.patched

Link: http://lkml.kernel.org/r/1392349908-29685-1-git-send-email-vnagarnaik@google.com

Cc: Laurent Chavey <chavey@google.com>
Cc: stable@vger.kernel.org # 3.10+
Signed-off-by: Vaibhav Nagarnaik <vnagarnaik@google.com>
Signed-off-by: Steven Rostedt <rostedt@goodmis.org>

2 files changed, 2 insertions, 9 deletions

diff --git a/include/linux/ftrace_event.h b/include/linux/ftrace_event.h
index 4e4cc28623ad..4cdb3a17bcb5 100644
--- a/include/linux/ftrace_event.h
+++ b/include/linux/ftrace_event.h
@@ -495,10 +495,6 @@ enum {
         FILTER_TRACE_FN,
 };
 
-#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,
                               const char *name, int offset, int size,
diff --git a/include/trace/ftrace.h b/include/trace/ftrace.h
index 1a8b28db3775..1ee19a24cc5f 100644
--- a/include/trace/ftrace.h
+++ b/include/trace/ftrace.h
@@ -310,15 +310,12 @@ static struct trace_event_functions ftrace_event_type_funcs_##call = {	\
 #undef __array
 #define __array(type, item, len)                                        \
         do {                                                            \
-                mutex_lock(&event_storage_mutex);                       \
+                char *type_str = #type"["__stringify(len)"]";           \
                 BUILD_BUG_ON(len > MAX_FILTER_STR_VAL);                 \
-                snprintf(event_storage, sizeof(event_storage),          \
-                         "%s[%d]", #type, len);                         \
-                ret = trace_define_field(event_call, event_storage, #item, \
+                ret = trace_define_field(event_call, type_str, #item,   \
                                  offsetof(typeof(field), item),         \
                                  sizeof(field.item),                    \
                                  is_signed_type(type), FILTER_OTHER);   \
-                mutex_unlock(&event_storage_mutex);                     \
                 if (ret)                                                \
                         return ret;                                     \
         } while (0);