filesystem: fix mountTimeout not working issue (prometheus#2903)

Signed-off-by: DongWei <jiangxuege@hotmail.com>

Author: DongWei-4

collector/filesystem_linux.go

@@ -122,16 +122,8 @@ func (c *filesystemCollector) processStat(labels filesystemLabels) filesystemSta
 
 	buf := new(unix.Statfs_t)
 	err := unix.Statfs(rootfsFilePath(labels.mountPoint), buf)
-	stuckMountsMtx.Lock()
 	close(success)
 
-	// If the mount has been marked as stuck, unmark it and log it's recovery.
-	if _, ok := stuckMounts[labels.mountPoint]; ok {
-		level.Debug(c.logger).Log("msg", "Mount point has recovered, monitoring will resume", "mountpoint", labels.mountPoint)
-		delete(stuckMounts, labels.mountPoint)
-	}
-	stuckMountsMtx.Unlock()
-
 	if err != nil {
 		level.Debug(c.logger).Log("msg", "Error on statfs() system call", "rootfs", rootfsFilePath(labels.mountPoint), "err", err)
 		return filesystemStats{
@@ -161,17 +153,29 @@ func stuckMountWatcher(mountPoint string, success chan struct{}, logger log.Logg
 	select {
 	case <-success:
 		// Success
+		// If the mount has been marked as stuck, unmark it and log it's recovery.
+		stuckMountsMtx.Lock()
+		defer stuckMountsMtx.Unlock()
+		if _, ok := stuckMounts[mountPoint]; ok {
+			level.Debug(logger).Log("msg", "Mount point has recovered, monitoring will resume", "mountpoint", mountPoint)
+			delete(stuckMounts, mountPoint)
+		}
 	case <-mountCheckTimer.C:
 		// Timed out, mark mount as stuck
 		stuckMountsMtx.Lock()
+		defer stuckMountsMtx.Unlock()
 		select {
 		case <-success:
 			// Success came in just after the timeout was reached, don't label the mount as stuck
+			// If the mount has been marked as stuck, unmark it and log it's recovery.
+			if _, ok := stuckMounts[mountPoint]; ok {
+				level.Debug(logger).Log("msg", "Mount point has recovered, monitoring will resume", "mountpoint", mountPoint)
+				delete(stuckMounts, mountPoint)
+			}
 		default:
 			level.Debug(logger).Log("msg", "Mount point timed out, it is being labeled as stuck and will not be monitored", "mountpoint", mountPoint)
 			stuckMounts[mountPoint] = struct{}{}
 		}
-		stuckMountsMtx.Unlock()
 	}
 }