From faef0a99c9fc805553b4a483dc1dfe0f6f7b3bfc Mon Sep 17 00:00:00 2001
From: Ben Johnson <benbjohnson@yahoo.com>
Date: Wed, 1 Feb 2017 10:40:58 -0700
Subject: [PATCH] Perform series tag iteration under lock.

Adds a `tsdb.Series.ForEachTag()` function for safely iterating
over a series' tags within the context of a lock. This preverts
tags from being dereferenced during iteration which can cause
a seg fault.
---
 CHANGELOG.md  | 1 +
 tsdb/meta.go  | 9 +++++++++
 tsdb/store.go | 6 +++---
 3 files changed, 13 insertions(+), 3 deletions(-)

diff --git a/CHANGELOG.md b/CHANGELOG.md
index 0574eaeb91..00356b7cf2 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -5,6 +5,7 @@
 - [#7877](https://github.com/influxdata/influxdb/issues/7877): Fix mapping of types when the measurement uses a regex
 - [#7888](https://github.com/influxdata/influxdb/pull/7888): Expand query dimensions from the subquery.
 - [#7910](https://github.com/influxdata/influxdb/issues/7910): Fix EvalType when a parenthesis expression is used.
+- [#7929](https://github.com/influxdata/influxdb/issues/7929): Fix series tag iteration segfault. (#7922)
 
 ## v1.2.0 [2017-01-24]
 
diff --git a/tsdb/meta.go b/tsdb/meta.go
index 52427eeee0..0723f74f1f 100644
--- a/tsdb/meta.go
+++ b/tsdb/meta.go
@@ -1620,6 +1620,15 @@ func (s *Series) ShardN() int {
 	return n
 }
 
+// ForEachTag executes fn for every tag. Iteration occurs under lock.
+func (s *Series) ForEachTag(fn func(models.Tag)) {
+	s.mu.RLock()
+	defer s.mu.RUnlock()
+	for _, t := range s.Tags {
+		fn(t)
+	}
+}
+
 // Dereference removes references to a byte slice.
 func (s *Series) Dereference(b []byte) {
 	s.mu.Lock()
diff --git a/tsdb/store.go b/tsdb/store.go
index d42d815c37..579418c913 100644
--- a/tsdb/store.go
+++ b/tsdb/store.go
@@ -926,14 +926,14 @@ func (s *Store) TagValues(database string, cond influxql.Expr) ([]TagValues, err
 		// Loop over all keys for each series.
 		m := make(map[KeyValue]struct{}, len(ss))
 		for _, series := range ss {
-			for _, t := range series.Tags {
+			series.ForEachTag(func(t models.Tag) {
 				if !ok {
 					// nop
 				} else if _, exists := keySet[string(t.Key)]; !exists {
-					continue
+					return
 				}
 				m[KeyValue{string(t.Key), string(t.Value)}] = struct{}{}
-			}
+			})
 		}
 
 		// Return an empty slice if there are no key/value matches.