sdk/db: do not hold the lock on Close

changelog/29097.txt

@@ -0,0 +1,3 @@
+```release-note:bug
+sdk/database: Fix a bug where slow database connections can cause goroutines to be blocked.
+```

sdk/database/dbplugin/v5/grpc_client.go

@@ -7,6 +7,8 @@ import (
 	"context"
 	"errors"
 	"fmt"
+	"os"
+	"strconv"
 	"time"
 
 	"github.com/golang/protobuf/ptypes"
@@ -270,7 +272,7 @@ func deleteUserRespFromProto(rpcResp *proto.DeleteUserResponse) (DeleteUserRespo
 }
 
 func (c gRPCClient) Type() (string, error) {
-	ctx, cancel := context.WithTimeout(context.Background(), 1*time.Second)
+	ctx, cancel := getContextWithTimeout(pluginutil.PluginGRPCTimeoutType)
 	defer cancel()
 
 	typeResp, err := c.client.Type(ctx, &proto.Empty{})
@@ -284,7 +286,7 @@ func (c gRPCClient) Type() (string, error) {
 }
 
 func (c gRPCClient) Close() error {
-	ctx, cancel := context.WithTimeout(context.Background(), 1*time.Second)
+	ctx, cancel := getContextWithTimeout(pluginutil.PluginGRPCTimeoutClose)
 	defer cancel()
 
 	_, err := c.client.Close(ctx, &proto.Empty{})
@@ -296,3 +298,11 @@ func (c gRPCClient) Close() error {
 	}
 	return nil
 }
+
+func getContextWithTimeout(env string) (context.Context, context.CancelFunc) {
+	timeout := 1 // default timeout
+	if envTimeout, err := strconv.Atoi(os.Getenv(env)); err == nil && envTimeout > 0 {
+		timeout = envTimeout
+	}
+	return context.WithTimeout(context.Background(), time.Duration(timeout)*time.Second)
+}

sdk/database/dbplugin/v5/grpc_server.go

@@ -290,27 +290,46 @@ func (g *gRPCServer) Type(ctx context.Context, _ *proto.Empty) (*proto.TypeRespo
 
 func (g *gRPCServer) Close(ctx context.Context, _ *proto.Empty) (*proto.Empty, error) {
 	g.Lock()
-	defer g.Unlock()
 
 	impl, err := g.getDatabaseInternal(ctx)
 	if err != nil {
+		g.Unlock()
 		return nil, err
 	}
 
-	err = impl.Close()
-	if err != nil {
-		return &proto.Empty{}, status.Errorf(codes.Internal, "unable to close database plugin: %s", err)
-	}
-
+	var id string
 	if g.singleImpl == nil {
 		// only cleanup instances map when multiplexing is supported
-		id, err := pluginutil.GetMultiplexIDFromContext(ctx)
+		id, err = pluginutil.GetMultiplexIDFromContext(ctx)
 		if err != nil {
+			g.Unlock()
 			return nil, err
 		}
 		delete(g.instances, id)
 	}
 
+	// unlock here so that the subsequent call to Close() does not hold the
+	// lock in case the DB is slow to respond
+	g.Unlock()
+
+	err = impl.Close()
+	if err != nil {
+		// The call to Close failed, so we will put the DB instance back in the
+		// map. This might not be necessary, but we do this in case anything
+		// relies on being able to retry Close.
+		g.Lock()
+		defer g.Unlock()
+		if g.singleImpl == nil {
+			// There is a chance that while we were calling Close another DB
+			// config was created for the old ID. So we only put it back if
+			// it's not set.
+			if _, ok := g.instances[id]; !ok {
+				g.instances[id] = impl
+			}
+		}
+		return &proto.Empty{}, status.Errorf(codes.Internal, "unable to close database plugin: %s", err)
+	}
+
 	return &proto.Empty{}, nil
 }
 

sdk/database/dbplugin/v5/grpc_server_test.go

@@ -551,6 +551,19 @@ func TestGRPCServer_Close(t *testing.T) {
 				}
 			},
 		},
+		"error path for multiplexed plugin": {
+			db: fakeDatabase{
+				closeErr: errors.New("close error"),
+			},
+			expectErr:     true,
+			expectCode:    codes.Internal,
+			grpcSetupFunc: testGrpcServer,
+			assertFunc: func(t *testing.T, g gRPCServer) {
+				if len(g.instances) != 1 {
+					t.Fatalf("err expected instances map to contain exactly 1 element")
+				}
+			},
+		},
 		"happy path for non-multiplexed plugin": {
 			db:            fakeDatabase{},
 			expectErr:     false,

sdk/helper/pluginutil/env.go

@@ -49,6 +49,14 @@ const (
 	// configuration as a shim to the pgx posgtres library.
 	// Deprecated: VAULT_PLUGIN_USE_POSTGRES_SSLINLINE will be removed in a future version of the Vault SDK.
 	PluginUsePostgresSSLInline = "VAULT_PLUGIN_USE_POSTGRES_SSLINLINE"
+
+	// PluginGRPCTimeoutType is an ENV name used to set the timeout for Vault's
+	// call to the plugin Type() GRPC method
+	PluginGRPCTimeoutType = "VAULT_PLUGIN_GRPC_TIMEOUT_TYPE"
+
+	// PluginGRPCTimeoutClose is an ENV name used to set the timeout for Vault's
+	// call to the plugin Close() GRPC method
+	PluginGRPCTimeoutClose = "VAULT_PLUGIN_GRPC_TIMEOUT_CLOSE"
 )
 
 // OptionallyEnableMlock determines if mlock should be called, and if so enables