[FIXED] Make sure to hold lock for duration of truncate (#5279)

Make sure to hold lock for duration of truncate, was calling slotInfo
unprotected.

Signed-off-by: Derek Collison <derek@nats.io>

server/filestore.go

@@ -4313,8 +4313,11 @@ func (mb *msgBlock) eraseMsg(seq uint64, ri, rl int) error {
 
 // Truncate this message block to the storedMsg.
 func (mb *msgBlock) truncate(sm *StoreMsg) (nmsgs, nbytes uint64, err error) {
+	mb.mu.Lock()
+	defer mb.mu.Unlock()
+
 	// Make sure we are loaded to process messages etc.
-	if err := mb.loadMsgs(); err != nil {
+	if err := mb.loadMsgsWithLock(); err != nil {
 		return 0, 0, err
 	}
 
@@ -4328,8 +4331,6 @@ func (mb *msgBlock) truncate(sm *StoreMsg) (nmsgs, nbytes uint64, err error) {
 
 	var purged, bytes uint64
 
-	mb.mu.Lock()
-
 	checkDmap := mb.dmap.Size() > 0
 	var smv StoreMsg
 
@@ -4365,28 +4366,24 @@ func (mb *msgBlock) truncate(sm *StoreMsg) (nmsgs, nbytes uint64, err error) {
 	if mb.cmp != NoCompression {
 		buf, err := mb.loadBlock(nil)
 		if err != nil {
-			mb.mu.Unlock()
 			return 0, 0, fmt.Errorf("failed to load block from disk: %w", err)
 		}
 		if mb.bek != nil && len(buf) > 0 {
 			bek, err := genBlockEncryptionKey(mb.fs.fcfg.Cipher, mb.seed, mb.nonce)
 			if err != nil {
-				mb.mu.Unlock()
 				return 0, 0, err
 			}
 			mb.bek = bek
 			mb.bek.XORKeyStream(buf, buf)
 		}
 		buf, err = mb.decompressIfNeeded(buf)
 		if err != nil {
-			mb.mu.Unlock()
 			return 0, 0, fmt.Errorf("failed to decompress block: %w", err)
 		}
 		buf = buf[:eof]
 		copy(mb.lchk[0:], buf[:len(buf)-checksumSize])
 		buf, err = mb.cmp.Compress(buf)
 		if err != nil {
-			mb.mu.Unlock()
 			return 0, 0, fmt.Errorf("failed to recompress block: %w", err)
 		}
 		meta := &CompressionInfo{
@@ -4397,19 +4394,16 @@ func (mb *msgBlock) truncate(sm *StoreMsg) (nmsgs, nbytes uint64, err error) {
 		if mb.bek != nil && len(buf) > 0 {
 			bek, err := genBlockEncryptionKey(mb.fs.fcfg.Cipher, mb.seed, mb.nonce)
 			if err != nil {
-				mb.mu.Unlock()
 				return 0, 0, err
 			}
 			mb.bek = bek
 			mb.bek.XORKeyStream(buf, buf)
 		}
 		n, err := mb.writeAt(buf, 0)
 		if err != nil {
-			mb.mu.Unlock()
 			return 0, 0, fmt.Errorf("failed to rewrite compressed block: %w", err)
 		}
 		if n != len(buf) {
-			mb.mu.Unlock()
 			return 0, 0, fmt.Errorf("short write (%d != %d)", n, len(buf))
 		}
 		mb.mfd.Truncate(int64(len(buf)))
@@ -4422,7 +4416,6 @@ func (mb *msgBlock) truncate(sm *StoreMsg) (nmsgs, nbytes uint64, err error) {
 		mb.mfd.ReadAt(lchk[:], eof-8)
 		copy(mb.lchk[0:], lchk[:])
 	} else {
-		mb.mu.Unlock()
 		return 0, 0, fmt.Errorf("failed to truncate msg block %d, file not open", mb.index)
 	}
 
@@ -4436,10 +4429,8 @@ func (mb *msgBlock) truncate(sm *StoreMsg) (nmsgs, nbytes uint64, err error) {
 	// Redo per subject info for this block.
 	mb.resetPerSubjectInfo()
 
-	mb.mu.Unlock()
-
 	// Load msgs again.
-	mb.loadMsgs()
+	mb.loadMsgsWithLock()
 
 	return purged, bytes, nil
 }