fix: rootdisk detection by not using cached value when GetDiskInfo() errors out (#15249)

GetDiskInfo() uses timedValue to cache the disk info for one second.

timedValue behavior was recently changed to return an old cached value
when calculating a new value returns an error.

When a mount point is empty, GetDiskInfo() will return errUnformattedDisk,
timedValue will return cached disk info with unexpected IsRootDisk value,
e.g. false if the mount point belongs to a root disk. Therefore, the mount
point will be considered a valid disk and will be formatted as well.

This commit will also add more defensive code when marking root disks:
always mark a disk offline for any GetDiskInfo() error except
errUnformattedDisk. The server will try anyway to reconnect to those
disks every 10 seconds.

cmd/erasure-sets.go

@@ -1165,8 +1165,12 @@ func markRootDisksAsDown(storageDisks []StorageAPI, errs []error) {
 		// Do nothing
 		return
 	}
-	infos, _ := getHealDiskInfos(storageDisks, errs)
+	infos, ierrs := getHealDiskInfos(storageDisks, errs)
 	for i := range storageDisks {
+		if ierrs[i] != nil && ierrs[i] != errUnformattedDisk {
+			storageDisks[i] = nil
+			continue
+		}
 		if storageDisks[i] != nil && infos[i].RootDisk {
 			// We should not heal on root disk. i.e in a situation where the minio-administrator has unmounted a
 			// defective drive we should not heal a path on the root disk.

cmd/metrics-v2.go

@@ -232,6 +232,7 @@ type MetricsGroup struct {
 // to populate new values upon cache invalidation.
 func (g *MetricsGroup) RegisterRead(read func(ctx context.Context) []Metric) {
 	g.metricsCache.Once.Do(func() {
+		g.metricsCache.Relax = true
 		g.metricsCache.TTL = g.cacheInterval
 		g.metricsCache.Update = func() (interface{}, error) {
 			return read(GlobalContext), nil

cmd/utils.go

@@ -931,6 +931,10 @@ type timedValue struct {
 	// Should be set before calling Get().
 	TTL time.Duration
 
+	// When set to true, return the last cached value
+	// even if updating the value errors out
+	Relax bool
+
 	// Once can be used to initialize values for lazy initialization.
 	// Should be set before calling Get().
 	Once sync.Once
@@ -951,6 +955,7 @@ func (t *timedValue) Get() (interface{}, error) {
 
 	v, err := t.Update()
 	if err != nil {
+		if t.Relax {
 			// if update fails, return current
 			// cached value along with error.
 			//
@@ -960,6 +965,8 @@ func (t *timedValue) Get() (interface{}, error) {
 			v = t.get(0)
 			return v, err
 		}
+		return v, err
+	}
 
 	t.update(v)
 	return v, nil