tracing: Add hist trigger support for stacktraces as keys

It's often useful to be able to use a stacktrace as a hash key, for
keeping a count of the number of times a particular call path resulted
in a trace event, for instance.  Add a special key named 'stacktrace'
which can be used as key in a 'keys=' param for this purpose:

    # echo hist:keys=stacktrace ... \
               [ if filter] > event/trigger

Link: http://lkml.kernel.org/r/87515e90b3785232a874a12156174635a348edb1.1457029949.git.tom.zanussi@linux.intel.com

Signed-off-by: Tom Zanussi <tom.zanussi@linux.intel.com>
Tested-by: Masami Hiramatsu <masami.hiramatsu.pt@hitachi.com>
Reviewed-by: Namhyung Kim <namhyung@kernel.org>
Signed-off-by: Steven Rostedt <rostedt@goodmis.org>

1 files changed, 101 insertions, 34 deletions

diff --git a/kernel/trace/trace_events_hist.c b/kernel/trace/trace_events_hist.c
index f9e7ecb33847..21cae42b54da 100644
--- a/kernel/trace/trace_events_hist.c
+++ b/kernel/trace/trace_events_hist.c
@@ -35,6 +35,11 @@ struct hist_field {
 	unsigned int			offset;
 };
 
+static u64 hist_field_none(struct hist_field *field, void *event)
+{
+	return 0;
+}
+
 static u64 hist_field_counter(struct hist_field *field, void *event)
 {
 	return 1;
@@ -73,8 +78,12 @@ DEFINE_HIST_FIELD_FN(u8);
 #define for_each_hist_key_field(i, hist_data)	\
 	for ((i) = (hist_data)->n_vals; (i) < (hist_data)->n_fields; (i)++)
 
+#define HIST_STACKTRACE_DEPTH	16
+#define HIST_STACKTRACE_SIZE	(HIST_STACKTRACE_DEPTH * sizeof(unsigned long))
+#define HIST_STACKTRACE_SKIP	5
+
 #define HITCOUNT_IDX		0
-#define HIST_KEY_SIZE_MAX	(MAX_FILTER_STR_VAL + sizeof(u64))
+#define HIST_KEY_SIZE_MAX	(MAX_FILTER_STR_VAL + HIST_STACKTRACE_SIZE)
 
 enum hist_field_flags {
 	HIST_FIELD_FL_HITCOUNT		= 1,
@@ -85,6 +94,7 @@ enum hist_field_flags {
 	HIST_FIELD_FL_SYM_OFFSET	= 32,
 	HIST_FIELD_FL_EXECNAME		= 64,
 	HIST_FIELD_FL_SYSCALL		= 128,
+	HIST_FIELD_FL_STACKTRACE	= 256,
 };
 
 struct hist_trigger_attrs {
@@ -323,6 +333,11 @@ static struct hist_field *create_hist_field(struct ftrace_event_field *field,
 		goto out;
 	}
 
+	if (flags & HIST_FIELD_FL_STACKTRACE) {
+		hist_field->fn = hist_field_none;
+		goto out;
+	}
+
 	if (is_string_field(field)) {
 		flags |= HIST_FIELD_FL_STRING;
 		hist_field->fn = hist_field_string;
@@ -456,7 +471,6 @@ static int create_key_field(struct hist_trigger_data *hist_data,
 	struct ftrace_event_field *field = NULL;
 	unsigned long flags = 0;
 	unsigned int key_size;
-	char *field_name;
 	int ret = 0;
 
 	if (WARN_ON(key_idx >= TRACING_MAP_FIELDS_MAX))
@@ -464,33 +478,39 @@ static int create_key_field(struct hist_trigger_data *hist_data,
 
 	flags |= HIST_FIELD_FL_KEY;
 
-	field_name = strsep(&field_str, ".");
-	if (field_str) {
-		if (strcmp(field_str, "hex") == 0)
-			flags |= HIST_FIELD_FL_HEX;
-		else if (strcmp(field_str, "sym") == 0)
-			flags |= HIST_FIELD_FL_SYM;
-		else if (strcmp(field_str, "sym-offset") == 0)
-			flags |= HIST_FIELD_FL_SYM_OFFSET;
-		else if ((strcmp(field_str, "execname") == 0) &&
-			 (strcmp(field_name, "common_pid") == 0))
-			flags |= HIST_FIELD_FL_EXECNAME;
-		else if (strcmp(field_str, "syscall") == 0)
-			flags |= HIST_FIELD_FL_SYSCALL;
-		else {
+	if (strcmp(field_str, "stacktrace") == 0) {
+		flags |= HIST_FIELD_FL_STACKTRACE;
+		key_size = sizeof(unsigned long) * HIST_STACKTRACE_DEPTH;
+	} else {
+		char *field_name = strsep(&field_str, ".");
+
+		if (field_str) {
+			if (strcmp(field_str, "hex") == 0)
+				flags |= HIST_FIELD_FL_HEX;
+			else if (strcmp(field_str, "sym") == 0)
+				flags |= HIST_FIELD_FL_SYM;
+			else if (strcmp(field_str, "sym-offset") == 0)
+				flags |= HIST_FIELD_FL_SYM_OFFSET;
+			else if ((strcmp(field_str, "execname") == 0) &&
+				 (strcmp(field_name, "common_pid") == 0))
+				flags |= HIST_FIELD_FL_EXECNAME;
+			else if (strcmp(field_str, "syscall") == 0)
+				flags |= HIST_FIELD_FL_SYSCALL;
+			else {
+				ret = -EINVAL;
+				goto out;
+			}
+		}
+
+		field = trace_find_event_field(file->event_call, field_name);
+		if (!field) {
 			ret = -EINVAL;
 			goto out;
 		}
-	}
 
-	field = trace_find_event_field(file->event_call, field_name);
-	if (!field) {
-		ret = -EINVAL;
-		goto out;
+		key_size = field->size;
 	}
 
-	key_size = field->size;
-
 	hist_data->fields[key_idx] = create_hist_field(field, flags);
 	if (!hist_data->fields[key_idx]) {
 		ret = -ENOMEM;
@@ -679,7 +699,9 @@ static int create_tracing_map_fields(struct hist_trigger_data *hist_data)
 
 			field = hist_field->field;
 
-			if (is_string_field(field))
+			if (hist_field->flags & HIST_FIELD_FL_STACKTRACE)
+				cmp_fn = tracing_map_cmp_none;
+			else if (is_string_field(field))
 				cmp_fn = tracing_map_cmp_string;
 			else
 				cmp_fn = tracing_map_cmp_num(field->size,
@@ -786,7 +808,9 @@ static void hist_trigger_elt_update(struct hist_trigger_data *hist_data,
 static void event_hist_trigger(struct event_trigger_data *data, void *rec)
 {
 	struct hist_trigger_data *hist_data = data->private_data;
+	unsigned long entries[HIST_STACKTRACE_DEPTH];
 	char compound_key[HIST_KEY_SIZE_MAX];
+	struct stack_trace stacktrace;
 	struct hist_field *key_field;
 	struct tracing_map_elt *elt;
 	u64 field_contents;
@@ -799,15 +823,27 @@ static void event_hist_trigger(struct event_trigger_data *data, void *rec)
 	for_each_hist_key_field(i, hist_data) {
 		key_field = hist_data->fields[i];
 
-		field_contents = key_field->fn(key_field, rec);
-		if (key_field->flags & HIST_FIELD_FL_STRING)
-			key = (void *)(unsigned long)field_contents;
-		else
-			key = (void *)&field_contents;
+		if (key_field->flags & HIST_FIELD_FL_STACKTRACE) {
+			stacktrace.max_entries = HIST_STACKTRACE_DEPTH;
+			stacktrace.entries = entries;
+			stacktrace.nr_entries = 0;
+			stacktrace.skip = HIST_STACKTRACE_SKIP;
 
-		if (hist_data->n_keys > 1) {
-			memcpy(compound_key + key_field->offset, key,
-			       key_field->size);
+			memset(stacktrace.entries, 0, HIST_STACKTRACE_SIZE);
+			save_stack_trace(&stacktrace);
+
+			key = entries;
+		} else {
+			field_contents = key_field->fn(key_field, rec);
+			if (key_field->flags & HIST_FIELD_FL_STRING)
+				key = (void *)(unsigned long)field_contents;
+			else
+				key = (void *)&field_contents;
+
+			if (hist_data->n_keys > 1) {
+				memcpy(compound_key + key_field->offset, key,
+				       key_field->size);
+			}
 		}
 	}
 
@@ -819,6 +855,24 @@ static void event_hist_trigger(struct event_trigger_data *data, void *rec)
 		hist_trigger_elt_update(hist_data, elt, rec);
 }
 
+static void hist_trigger_stacktrace_print(struct seq_file *m,
+					  unsigned long *stacktrace_entries,
+					  unsigned int max_entries)
+{
+	char str[KSYM_SYMBOL_LEN];
+	unsigned int spaces = 8;
+	unsigned int i;
+
+	for (i = 0; i < max_entries; i++) {
+		if (stacktrace_entries[i] == ULONG_MAX)
+			return;
+
+		seq_printf(m, "%*c", 1 + spaces, ' ');
+		sprint_symbol(str, stacktrace_entries[i]);
+		seq_printf(m, "%s\n", str);
+	}
+}
+
 static void
 hist_trigger_entry_print(struct seq_file *m,
 			 struct hist_trigger_data *hist_data, void *key,
@@ -826,6 +880,7 @@ hist_trigger_entry_print(struct seq_file *m,
 {
 	struct hist_field *key_field;
 	char str[KSYM_SYMBOL_LEN];
+	bool multiline = false;
 	unsigned int i;
 	u64 uval;
 
@@ -867,6 +922,12 @@ hist_trigger_entry_print(struct seq_file *m,
 
 			seq_printf(m, "%s: %-30s[%3llu]",
 				   key_field->field->name, syscall_name, uval);
+		} else if (key_field->flags & HIST_FIELD_FL_STACKTRACE) {
+			seq_puts(m, "stacktrace:\n");
+			hist_trigger_stacktrace_print(m,
+						      key + key_field->offset,
+						      HIST_STACKTRACE_DEPTH);
+			multiline = true;
 		} else if (key_field->flags & HIST_FIELD_FL_STRING) {
 			seq_printf(m, "%s: %-50s", key_field->field->name,
 				   (char *)(key + key_field->offset));
@@ -877,7 +938,10 @@ hist_trigger_entry_print(struct seq_file *m,
 		}
 	}
 
-	seq_puts(m, " }");
+	if (!multiline)
+		seq_puts(m, " ");
+
+	seq_puts(m, "}");
 
 	seq_printf(m, " hitcount: %10llu",
 		   tracing_map_read_sum(elt, HITCOUNT_IDX));
@@ -1021,7 +1085,10 @@ static int event_hist_trigger_print(struct seq_file *m,
 		if (i > hist_data->n_vals)
 			seq_puts(m, ",");
 
-		hist_field_print(m, key_field);
+		if (key_field->flags & HIST_FIELD_FL_STACKTRACE)
+			seq_puts(m, "stacktrace");
+		else
+			hist_field_print(m, key_field);
 	}
 
 	seq_puts(m, ":vals=");