Pull request 2646: 8359-fix-deadlock

Updates #8359.

Squashed commit of the following:

commit 3242b00261ddcf37632999a992e2b81eae5a7f95
Author: Eugene Burkov <E.Burkov@AdGuard.COM>
Date:   Thu Apr 30 14:10:13 2026 +0300

    stats: imp code

commit b7bf300f8744b53f6cd49ce37ebd36c970da5630
Author: Eugene Burkov <E.Burkov@AdGuard.COM>
Date:   Wed Apr 29 22:28:59 2026 +0300

    all: fix deadlock

CHANGELOG.md

@@ -28,6 +28,8 @@ NOTE: Add new changes BELOW THIS COMMENT.
 
 ### Fixed
 
+- Statistics database deadlock ([#8359]).
+
 - Translated labels on the DNS settings pages not updating after changing the UI language.
 
 - Dashboard charts now correctly display lower query counts ([#6823]).

client/src/__tests__/checkRedirect.test.ts

@@ -45,4 +45,4 @@ describe('checkRedirect', () => {
         expect(fetchMock).toHaveBeenCalledTimes(2);
         expect(console.error).toHaveBeenCalled();
     });
-});
+});

client/src/__tests__/checkStatus.test.ts

@@ -52,4 +52,4 @@ describe('checkStatus', () => {
         expect(handleRequestError).toHaveBeenCalledTimes(1);
         expect(fetch).not.toHaveBeenCalled();
     });
-});
+});

client/src/__tests__/fetchRequest.test.ts

@@ -74,4 +74,4 @@ describe('apiClient.makeRequest', () => {
         expect(result).toBe(false);
         expect(window.location.pathname).not.toBe(HTML_PAGES.LOGIN);
     });
-});
+});

client/src/api/fetch.ts

@@ -68,4 +68,4 @@ export const fetchRequest = async (url: string, method = 'GET', config: RequestC
         data: responseData,
         status: response.status,
     };
-};
+};

client/src/components/ui/lineUtils.ts

@@ -39,4 +39,4 @@ export const buildChartData = (
         index,
         value,
         label: formatHistoryLabel(index, interval, timeUnits, now),
-    }));
+    }));

internal/stats/stats.go

@@ -257,17 +257,19 @@ func (s *StatsCtx) Close() (err error) {
 		err = errors.WithDeferred(err, cerr)
 	}()
 
+	// NOTE:  This mutex, when combined with the database transaction, is
+	// required to be locked first.
+	s.currMu.RLock()
+	defer s.currMu.RUnlock()
+
+	udb := s.curr.serialize()
+
 	tx, err := db.Begin(true)
 	if err != nil {
 		return fmt.Errorf("opening transaction: %w", err)
 	}
 	defer func() { err = errors.WithDeferred(err, finishTxn(tx, err == nil)) }()
 
-	s.currMu.RLock()
-	defer s.currMu.RUnlock()
-
-	udb := s.curr.serialize()
-
 	return s.flushUnitToDB(udb, tx, s.curr.id)
 }
 
@@ -421,6 +423,8 @@ func (s *StatsCtx) flush() (cont bool, sleepFor time.Duration) {
 	s.confMu.Lock()
 	defer s.confMu.Unlock()
 
+	// NOTE:  This mutex, when combined with the database transaction, is
+	// required to be locked first.
 	s.currMu.Lock()
 	defer s.currMu.Unlock()
 
@@ -571,6 +575,11 @@ func (s *StatsCtx) loadUnits(limit uint32) (units []*unitDB, curID uint32) {
 		return nil, 0
 	}
 
+	// NOTE:  This mutex, when combined with the database transaction, is
+	// required to be locked first.
+	s.currMu.RLock()
+	defer s.currMu.RUnlock()
+
 	// Use writable transaction to ensure any ongoing writable transaction is
 	// taken into account.
 	tx, err := db.Begin(true)
@@ -579,10 +588,6 @@ func (s *StatsCtx) loadUnits(limit uint32) (units []*unitDB, curID uint32) {
 
 		return nil, 0
 	}
-
-	s.currMu.RLock()
-	defer s.currMu.RUnlock()
-
 	cur := s.curr
 
 	if cur != nil {