tracing: add lock depth to entries

This patch adds the lock depth of the big kernel lock to the generic
entry header. This way we can see the depth of the lock and help
in removing the BKL.

Example:

 #                  _------=> CPU#
 #                 / _-----=> irqs-off
 #                | / _----=> need-resched
 #                || / _---=> hardirq/softirq
 #                ||| / _--=> preempt-depth
 #                |||| /_--=> lock-depth
 #                |||||/     delay
 #  cmd     pid   |||||| time  |   caller
 #     \   /      ||||||   \   |   /
   <idle>-0       2.N..3 5902255250us+: lock_acquire: read rcu_read_lock
   <idle>-0       2.N..3 5902255253us+: lock_release: rcu_read_lock
   <idle>-0       2dN..3 5902255257us+: lock_acquire: xtime_lock
   <idle>-0       2dN..4 5902255259us : lock_acquire: clocksource_lock
   <idle>-0       2dN..4 5902255261us+: lock_release: clocksource_lock

Signed-off-by: Steven Rostedt <rostedt@goodmis.org>

1 files changed, 4 insertions, 1 deletions

diff --git a/kernel/trace/trace_events.c b/kernel/trace/trace_events.c
index 28d92027a93c..975f324a07e7 100644
--- a/kernel/trace/trace_events.c
+++ b/kernel/trace/trace_events.c
@@ -86,6 +86,7 @@ int trace_define_common_fields(struct ftrace_event_call *call)
         __common_field(unsigned char, flags);
         __common_field(unsigned char, preempt_count);
         __common_field(int, pid);
+        __common_field(int, lock_depth);
 
         return ret;
 }
@@ -571,11 +572,13 @@ static int trace_write_header(struct trace_seq *s)
                                 "\tfield:%s %s;\toffset:%zu;\tsize:%zu;\n"
                                 "\tfield:%s %s;\toffset:%zu;\tsize:%zu;\n"
                                 "\tfield:%s %s;\toffset:%zu;\tsize:%zu;\n"
+                                "\tfield:%s %s;\toffset:%zu;\tsize:%zu;\n"
                                 "\n",
                                 FIELD(unsigned short, type),
                                 FIELD(unsigned char, flags),
                                 FIELD(unsigned char, preempt_count),
-                                FIELD(int, pid));
+                                FIELD(int, pid),
+                                FIELD(int, lock_depth));
 }
 
 static ssize_t