etcdserver: fix corruption check when server has just been compacted

When a key-value store corruption check happens immediately after a
compaction, the revision at which the key-value store hash is computed,
is the compacted revision itself.
In that case, the hash computation logic was incorrect because it
returned an ErrCompacted error; this error should instead be returned when
the revision at which the key-value store is hashed, is strictly lower
than the compacted revision.

Fixes #14325

Signed-off-by: Jeremy Leach <44558776+jbml@users.noreply.github.com>

server/mvcc/kvstore.go

@@ -175,7 +175,7 @@ func (s *store) hashByRev(rev int64) (hash KeyValueHash, currentRev int64, err e
 	compactRev, currentRev = s.compactMainRev, s.currentRev
 	s.revMu.RUnlock()
 
-	if rev > 0 && rev <= compactRev {
+	if rev > 0 && rev < compactRev {
 		s.mu.RUnlock()
 		return KeyValueHash{}, 0, ErrCompacted
 	} else if rev > 0 && rev > currentRev {

server/mvcc/kvstore_test.go

@@ -40,6 +40,7 @@ import (
 	"go.etcd.io/etcd/server/v3/mvcc/buckets"
 
 	"go.uber.org/zap"
+	"go.uber.org/zap/zaptest"
 )
 
 func TestStoreRev(t *testing.T) {
@@ -536,17 +537,18 @@ type hashKVResult struct {
 func TestHashKVWhenCompacting(t *testing.T) {
 	b, tmpPath := betesting.NewDefaultTmpBackend(t)
 	s := NewStore(zap.NewExample(), b, &lease.FakeLessor{}, StoreConfig{})
-	defer os.Remove(tmpPath)
+	defer cleanup(s, b, tmpPath)
 
 	rev := 10000
 	for i := 2; i <= rev; i++ {
 		s.Put([]byte("foo"), []byte(fmt.Sprintf("bar%d", i)), lease.NoLease)
 	}
 
 	hashCompactc := make(chan hashKVResult, 1)
-
-	donec := make(chan struct{})
 	var wg sync.WaitGroup
+	donec := make(chan struct{})
+
+	// Call HashByRev(10000) in multiple goroutines until donec is closed
 	for i := 0; i < 10; i++ {
 		wg.Add(1)
 		go func() {
@@ -565,28 +567,39 @@ func TestHashKVWhenCompacting(t *testing.T) {
 		}()
 	}
 
+	// Check computed hashes by HashByRev are correct in a goroutine, until donec is closed
+	wg.Add(1)
 	go func() {
-		defer close(donec)
+		defer wg.Done()
 		revHash := make(map[int64]uint32)
-		for round := 0; round < 1000; round++ {
+		for {
 			r := <-hashCompactc
 			if revHash[r.compactRev] == 0 {
 				revHash[r.compactRev] = r.hash
 			}
 			if r.hash != revHash[r.compactRev] {
 				t.Errorf("Hashes differ (current %v) != (saved %v)", r.hash, revHash[r.compactRev])
 			}
+
+			select {
+			case <-donec:
+				return
+			default:
+			}
 		}
 	}()
 
-	wg.Add(1)
+	// Compact the store in a goroutine, using revision 9900 to 10000 and close donec when finished
 	go func() {
-		defer wg.Done()
+		defer close(donec)
 		for i := 100; i >= 0; i-- {
-			_, err := s.Compact(traceutil.TODO(), int64(rev-1-i))
+			_, err := s.Compact(traceutil.TODO(), int64(rev-i))
 			if err != nil {
 				t.Error(err)
 			}
+			// Wait for the compaction job to finish
+			s.fifoSched.WaitFinish(1)
+			// Leave time for calls to HashByRev to take place after each compaction
 			time.Sleep(10 * time.Millisecond)
 		}
 	}()
@@ -599,12 +612,45 @@ func TestHashKVWhenCompacting(t *testing.T) {
 	}
 }
 
+// TestHashKVWithCompactedAndFutureRevisions ensures that HashKV returns a correct hash when called
+// with a past revision (lower than compacted), a future revision, and the exact compacted revision
+func TestHashKVWithCompactedAndFutureRevisions(t *testing.T) {
+	b, tmpPath := betesting.NewDefaultTmpBackend(t)
+	s := NewStore(zaptest.NewLogger(t), b, &lease.FakeLessor{}, StoreConfig{})
+	defer cleanup(s, b, tmpPath)
+
+	rev := 10000
+	compactRev := rev / 2
+
+	for i := 2; i <= rev; i++ {
+		s.Put([]byte("foo"), []byte(fmt.Sprintf("bar%d", i)), lease.NoLease)
+	}
+	if _, err := s.Compact(traceutil.TODO(), int64(compactRev)); err != nil {
+		t.Fatal(err)
+	}
+
+	_, _, errFutureRev := s.HashStorage().HashByRev(int64(rev + 1))
+	if errFutureRev != ErrFutureRev {
+		t.Error(errFutureRev)
+	}
+
+	_, _, errPastRev := s.HashStorage().HashByRev(int64(compactRev - 1))
+	if errPastRev != ErrCompacted {
+		t.Error(errPastRev)
+	}
+
+	_, _, errCompactRev := s.HashStorage().HashByRev(int64(compactRev))
+	if errCompactRev != nil {
+		t.Error(errCompactRev)
+	}
+}
+
 // TestHashKVZeroRevision ensures that "HashByRev(0)" computes
 // correct hash value with latest revision.
 func TestHashKVZeroRevision(t *testing.T) {
 	b, tmpPath := betesting.NewDefaultTmpBackend(t)
 	s := NewStore(zap.NewExample(), b, &lease.FakeLessor{}, StoreConfig{})
-	defer os.Remove(tmpPath)
+	defer cleanup(s, b, tmpPath)
 
 	rev := 10000
 	for i := 2; i <= rev; i++ {