From 4bb8c6f7d0be1aa8a42138b0f610945ca672e36b Mon Sep 17 00:00:00 2001
From: Vitaliy Filippov <vitalif@yourcmc.ru>
Date: Wed, 20 Dec 2023 17:06:54 +0300
Subject: [PATCH] Fix missing dirty part refcnt++ leading to fsync hangs

---
 internal/buffer_list.go      | 16 ++++++++--------
 internal/buffer_list_test.go | 18 ++++++++++++------
 2 files changed, 20 insertions(+), 14 deletions(-)

diff --git a/internal/buffer_list.go b/internal/buffer_list.go
index 8b45dc04..9948999c 100644
--- a/internal/buffer_list.go
+++ b/internal/buffer_list.go
@@ -256,14 +256,13 @@ func (l *BufferList) unqueue(b *FileBuffer) {
 		ep := l.helpers.PartNum(b.offset+b.length-1)
 		for i := sp; i < ep+1; i++ {
 			p := l.dirtyParts[i]
-			if p != nil {
-				p.refcnt--
-				if p.refcnt < 0 {
-					panic("BUG: dirty buffer count of part < 0")
-				} else if p.refcnt == 0 {
-					l.dirtyQueue.Delete(p.queueId)
-					delete(l.dirtyParts, i)
-				}
+			if p == nil || p.refcnt == 0 {
+				panic("BUG: dirty buffer count of part < 0")
+			}
+			p.refcnt--
+			if p.refcnt == 0 {
+				l.dirtyQueue.Delete(p.queueId)
+				delete(l.dirtyParts, i)
 			}
 		}
 	} else if b.state == BUF_CLEAN || b.state == BUF_FLUSHED_FULL {
@@ -280,6 +279,7 @@ func (l *BufferList) referenceDirtyPart(partNum uint64) {
 		l.dirtyQueue.Set(p.queueId, p)
 	} else {
 		l.dirtyQueue.Delete(p.queueId)
+		p.refcnt++
 		p.queueId = l.dirtyQid
 		l.dirtyQueue.Set(p.queueId, p)
 	}
diff --git a/internal/buffer_list_test.go b/internal/buffer_list_test.go
index add05d02..70aa2bf2 100644
--- a/internal/buffer_list_test.go
+++ b/internal/buffer_list_test.go
@@ -74,25 +74,31 @@ func (s *BufferListTest) TestSplitDirtyQueue(t *C) {
 	zeroed, allocated := l.ZeroRange(0, 100*1024)
 	t.Assert(zeroed, Equals, true)
 	t.Assert(allocated, Equals, int64(0))
-	// 6*1024 and 12*1024 isn't part boundary, refcnt of part 2 and 3 = 2, 1 and others = 1
-	t.Assert(l.Add(0, make([]byte, 6*1024), BUF_DIRTY, false), Equals, int64(6*1024))
+	// 6*1024 and 12*1024 isn't part boundary, refcnts should be: 4 2 2 1 1 ... 1
+	t.Assert(l.Add(0*1024, make([]byte, 1*1024), BUF_DIRTY, false), Equals, int64(1*1024))
+	t.Assert(l.Add(1*1024, make([]byte, 2*1024), BUF_DIRTY, false), Equals, int64(2*1024))
+	t.Assert(l.Add(3*1024, make([]byte, 3*1024), BUF_DIRTY, false), Equals, int64(3*1024))
 	t.Assert(l.Add(6*1024, make([]byte, 6*1024), BUF_DIRTY, false), Equals, int64(6*1024))
 	data, ids, err := l.GetData(12*1024, (100-12)*1024, true)
 	t.Assert(err, IsNil)
 	t.Assert(len(data), Equals, 1)
 	t.Assert(len(data[0]), Equals, (100-12)*1024)
 	t.Assert(ids, DeepEquals, map[uint64]bool{
-		4: true,
+		8: true,
 	})
 	l.SetState(12*1024, (100-12)*1024, ids, BUF_CLEAN)
 	data, ids, err = l.GetData(0, 12*1024, true)
 	t.Assert(err, IsNil)
-	t.Assert(len(data), Equals, 2)
-	t.Assert(len(data[0]), Equals, 6*1024)
-	t.Assert(len(data[1]), Equals, 6*1024)
+	t.Assert(len(data), Equals, 4)
+	t.Assert(len(data[0]), Equals, 1*1024)
+	t.Assert(len(data[1]), Equals, 2*1024)
+	t.Assert(len(data[2]), Equals, 3*1024)
+	t.Assert(len(data[3]), Equals, 6*1024)
 	t.Assert(ids, DeepEquals, map[uint64]bool{
 		3: true,
 		5: true,
+		7: true,
+		9: true,
 	})
 	l.SetState(0, 12*1024, ids, BUF_CLEAN)
 	// Now check dirty list - it should be empty