From e9461686b87496c5d60e7ce8899865f267c3abc1 Mon Sep 17 00:00:00 2001
From: Pavel Karpy <p.karpy@yadro.com>
Date: Thu, 20 Apr 2023 18:51:16 +0300
Subject: [PATCH] [#274] wc: Resolve possible deadlock

If operation with WC are _fast enough_ (e.g. `Init` failed and `Close` is
called immediately) there is a race and a deadlock that do not allow finish
(and start, in fact) an initialization routine because of taken `modeMtx`
and also do not allow finish `Close` call because of awaiting initialization
finish. So do stop initialization _before_ any mutex is taken.

Signed-off-by: Pavel Karpy <p.karpy@yadro.com>
---
 pkg/local_object_storage/writecache/mode.go   | 20 +++++++++----------
 .../writecache/writecache.go                  |  3 ---
 2 files changed, 10 insertions(+), 13 deletions(-)

diff --git a/pkg/local_object_storage/writecache/mode.go b/pkg/local_object_storage/writecache/mode.go
index 20b0cce298..14f8af49ef 100644
--- a/pkg/local_object_storage/writecache/mode.go
+++ b/pkg/local_object_storage/writecache/mode.go
@@ -29,9 +29,6 @@ func (c *cache) SetMode(m mode.Mode) error {
 		))
 	defer span.End()
 
-	c.modeMtx.Lock()
-	defer c.modeMtx.Unlock()
-
 	return c.setMode(ctx, m)
 }
 
@@ -40,13 +37,6 @@ func (c *cache) setMode(ctx context.Context, m mode.Mode) error {
 	var err error
 	turnOffMeta := m.NoMetabase()
 
-	if turnOffMeta && !c.mode.NoMetabase() {
-		err = c.flush(ctx, true)
-		if err != nil {
-			return err
-		}
-	}
-
 	if !c.initialized.Load() {
 		close(c.stopInitCh)
 
@@ -60,6 +50,16 @@ func (c *cache) setMode(ctx context.Context, m mode.Mode) error {
 		}()
 	}
 
+	c.modeMtx.Lock()
+	defer c.modeMtx.Unlock()
+
+	if turnOffMeta && !c.mode.NoMetabase() {
+		err = c.flush(ctx, true)
+		if err != nil {
+			return err
+		}
+	}
+
 	if c.db != nil {
 		if err = c.db.Close(); err != nil {
 			return fmt.Errorf("can't close write-cache database: %w", err)
diff --git a/pkg/local_object_storage/writecache/writecache.go b/pkg/local_object_storage/writecache/writecache.go
index 0fc2e601a1..bdcc9bbf6f 100644
--- a/pkg/local_object_storage/writecache/writecache.go
+++ b/pkg/local_object_storage/writecache/writecache.go
@@ -163,9 +163,6 @@ func (c *cache) Init() error {
 
 // Close closes db connection and stops services. Executes ObjectCounters.FlushAndClose op.
 func (c *cache) Close() error {
-	c.modeMtx.Lock()
-	defer c.modeMtx.Unlock()
-
 	// Finish all in-progress operations.
 	if err := c.setMode(context.TODO(), mode.ReadOnly); err != nil {
 		return err