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>

include/linux/ftrace_event.h

@@ -34,6 +34,7 @@ struct trace_entry {
 	unsigned char		flags;
 	unsigned char		preempt_count;
 	int			pid;
+	int			lock_depth;
 };
 
 #define FTRACE_MAX_EVENT						\

kernel/trace/trace.c

@@ -886,6 +886,7 @@ tracing_generic_entry_update(struct trace_entry *entry, unsigned long flags,
 
 	entry->preempt_count		= pc & 0xff;
 	entry->pid			= (tsk) ? tsk->pid : 0;
+	entry->lock_depth		= (tsk) ? tsk->lock_depth : 0;
 	entry->flags =
 #ifdef CONFIG_TRACE_IRQFLAGS_SUPPORT
 		(irqs_disabled_flags(flags) ? TRACE_FLAG_IRQS_OFF : 0) |
@@ -1530,10 +1531,10 @@ static void print_lat_help_header(struct seq_file *m)
 	seq_puts(m, "#                | / _----=> need-resched    \n");
 	seq_puts(m, "#                || / _---=> hardirq/softirq \n");
 	seq_puts(m, "#                ||| / _--=> preempt-depth   \n");
-	seq_puts(m, "#                |||| /                      \n");
-	seq_puts(m, "#                |||||     delay             \n");
-	seq_puts(m, "#  cmd     pid   ||||| time  |   caller      \n");
-	seq_puts(m, "#     \\   /      |||||   \\   |   /           \n");
+	seq_puts(m, "#                |||| /_--=> lock-depth       \n");
+	seq_puts(m, "#                |||||/     delay             \n");
+	seq_puts(m, "#  cmd     pid   |||||| time  |   caller      \n");
+	seq_puts(m, "#     \\   /      ||||||   \\   |   /           \n");
 }
 
 static void print_func_help_header(struct seq_file *m)

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

kernel/trace/trace_functions_graph.c

@@ -368,6 +368,7 @@ static enum print_line_t
 print_graph_lat_fmt(struct trace_seq *s, struct trace_entry *entry)
 {
 	int hardirq, softirq;
+	int ret;
 
 	hardirq = entry->flags & TRACE_FLAG_HARDIRQ;
 	softirq = entry->flags & TRACE_FLAG_SOFTIRQ;
@@ -382,6 +383,13 @@ print_graph_lat_fmt(struct trace_seq *s, struct trace_entry *entry)
 				hardirq ? 'h' : softirq ? 's' : '.'))
 		return 0;
 
+	if (entry->lock_depth < 0)
+		ret = trace_seq_putc(s, '.');
+	else
+		ret = trace_seq_printf(s, "%d", entry->lock_depth);
+	if (!ret)
+		return 0;
+
 	if (entry->preempt_count)
 		return trace_seq_printf(s, "%x", entry->preempt_count);
 	return trace_seq_puts(s, ".");
@@ -1001,8 +1009,8 @@ static void print_lat_header(struct seq_file *s)
 	seq_printf(s, "#%.*s / _----=> need-resched    \n", size, spaces);
 	seq_printf(s, "#%.*s| / _---=> hardirq/softirq \n", size, spaces);
 	seq_printf(s, "#%.*s|| / _--=> preempt-depth   \n", size, spaces);
-	seq_printf(s, "#%.*s||| /                      \n", size, spaces);
-	seq_printf(s, "#%.*s||||                       \n", size, spaces);
+	seq_printf(s, "#%.*s||| / _-=> lock-depth      \n", size, spaces);
+	seq_printf(s, "#%.*s|||| /                     \n", size, spaces);
 }
 
 static void print_graph_headers(struct seq_file *s)
@@ -1021,7 +1029,7 @@ static void print_graph_headers(struct seq_file *s)
 	if (tracer_flags.val & TRACE_GRAPH_PRINT_PROC)
 		seq_printf(s, "  TASK/PID       ");
 	if (lat)
-		seq_printf(s, "||||");
+		seq_printf(s, "|||||");
 	if (tracer_flags.val & TRACE_GRAPH_PRINT_DURATION)
 		seq_printf(s, "  DURATION   ");
 	seq_printf(s, "               FUNCTION CALLS\n");
@@ -1035,7 +1043,7 @@ static void print_graph_headers(struct seq_file *s)
 	if (tracer_flags.val & TRACE_GRAPH_PRINT_PROC)
 		seq_printf(s, "   |    |        ");
 	if (lat)
-		seq_printf(s, "||||");
+		seq_printf(s, "|||||");
 	if (tracer_flags.val & TRACE_GRAPH_PRINT_DURATION)
 		seq_printf(s, "   |   |      ");
 	seq_printf(s, "               |   |   |   |\n");

kernel/trace/trace_output.c

@@ -465,6 +465,7 @@ lat_print_generic(struct trace_seq *s, struct trace_entry *entry, int cpu)
 {
 	int hardirq, softirq;
 	char comm[TASK_COMM_LEN];
+	int ret;
 
 	trace_find_cmdline(entry->pid, comm);
 	hardirq = entry->flags & TRACE_FLAG_HARDIRQ;
@@ -481,9 +482,16 @@ lat_print_generic(struct trace_seq *s, struct trace_entry *entry, int cpu)
 				hardirq ? 'h' : softirq ? 's' : '.'))
 		return 0;
 
+	if (entry->lock_depth < 0)
+		ret = trace_seq_putc(s, '.');
+	else
+		ret = trace_seq_printf(s, "%d", entry->lock_depth);
+	if (!ret)
+		return 0;
+
 	if (entry->preempt_count)
 		return trace_seq_printf(s, "%x", entry->preempt_count);
-	return trace_seq_puts(s, ".");
+	return trace_seq_putc(s, '.');
 }
 
 static unsigned long preempt_mark_thresh = 100;