Remove UB when taking internal logs and move them to the final zapcore.Core (#14009)

Signed-off-by: Bogdan Drutu <[email protected]>

Author: bogdandrutu

.chloggen/fix-buffered-code-ub.yaml

@@ -0,0 +1,25 @@
+# Use this changelog template to create an entry for release notes.
+
+# One of 'breaking', 'deprecation', 'new_component', 'enhancement', 'bug_fix'
+change_type: bug_fix
+
+# The name of the component, or a single word describing the area of concern, (e.g. otlpreceiver)
+component: pkg/otelcol
+
+# A brief description of the change.  Surround your text with quotes ("") if it needs to start with a backtick (`).
+note: Remove UB when taking internal logs and move them to the final zapcore.Core
+
+# One or more tracking issues or pull requests related to the change
+issues: [14009]
+
+# (Optional) One or more lines of additional information to render under the primary note.
+# These lines will be padded with 2 spaces and then inserted directly into the document.
+# Use pipe (|) for multiline entries.
+subtext: This can happen because of a race on accessing `logsTaken`.
+
+# Optional: The change log or logs in which this entry should be included.
+# e.g. '[user]' or '[user, api]'
+# Include 'user' if the change is relevant to end users.
+# Include 'api' if there is a change to a library API.
+# Default: '[user]'
+change_logs: [user]

otelcol/buffered_core.go

@@ -25,7 +25,7 @@ var _ zapcore.Core = (*bufferedCore)(nil)
 
 type bufferedCore struct {
 	zapcore.LevelEnabler
-	mu        sync.RWMutex
+	mu        sync.Mutex
 	logs      []loggedEntry
 	context   []zapcore.Field
 	logsTaken bool
@@ -69,13 +69,13 @@ func (bc *bufferedCore) Sync() error {
 }
 
 func (bc *bufferedCore) TakeLogs() []loggedEntry {
-	if !bc.logsTaken {
-		bc.mu.Lock()
-		defer bc.mu.Unlock()
-		logs := bc.logs
-		bc.logs = nil
-		bc.logsTaken = true
-		return logs
+	bc.mu.Lock()
+	defer bc.mu.Unlock()
+	if bc.logsTaken {
+		return nil
 	}
-	return nil
+	logs := bc.logs
+	bc.logs = nil
+	bc.logsTaken = true
+	return logs
 }