From e2f5b0dd6012f2d439db6d7012492acf99d4f78f Mon Sep 17 00:00:00 2001
From: Davies Liu <davies@juicedata.io>
Date: Mon, 20 Nov 2023 15:39:29 +0800
Subject: [PATCH] meta: convert current write lock into read lock (#4179)

flock should convert current exclusive lock into a shared lock.
---
 pkg/meta/base_test.go  |  6 ++++++
 pkg/meta/redis_lock.go |  2 +-
 pkg/meta/sql_lock.go   | 18 +++++++++---------
 pkg/meta/tkv_lock.go   |  4 ++--
 4 files changed, 18 insertions(+), 12 deletions(-)

diff --git a/pkg/meta/base_test.go b/pkg/meta/base_test.go
index 3808f1c6bb53..0ce9b7b3f4f7 100644
--- a/pkg/meta/base_test.go
+++ b/pkg/meta/base_test.go
@@ -860,6 +860,12 @@ func testLocks(t *testing.T, m Meta) {
 	if st := m.Flock(ctx, inode, o1, syscall.F_WRLCK, false); st != 0 {
 		t.Fatalf("flock wlock: %s", st)
 	}
+	if st := m.Flock(ctx, inode, o1, syscall.F_RDLCK, false); st != 0 {
+		t.Fatalf("flock rlock: %s", st)
+	}
+	if st := m.Flock(ctx, inode, o1, syscall.F_WRLCK, false); st != 0 {
+		t.Fatalf("flock wlock: %s", st)
+	}
 	if st := m.Flock(ctx, inode, o1, syscall.F_UNLCK, false); st != 0 {
 		t.Fatalf("flock unlock: %s", st)
 	}
diff --git a/pkg/meta/redis_lock.go b/pkg/meta/redis_lock.go
index 075c852968d5..897964a44200 100644
--- a/pkg/meta/redis_lock.go
+++ b/pkg/meta/redis_lock.go
@@ -55,6 +55,7 @@ func (r *redisMeta) Flock(ctx Context, inode Ino, owner uint64, ltype uint32, bl
 			if err != nil {
 				return err
 			}
+			delete(owners, lkey)
 			if ltype == F_RDLCK {
 				for _, v := range owners {
 					if v == "W" {
@@ -67,7 +68,6 @@ func (r *redisMeta) Flock(ctx Context, inode Ino, owner uint64, ltype uint32, bl
 				})
 				return err
 			}
-			delete(owners, lkey)
 			if len(owners) > 0 {
 				return syscall.EAGAIN
 			}
diff --git a/pkg/meta/sql_lock.go b/pkg/meta/sql_lock.go
index 3f22282329cf..3dcd356aa3f8 100644
--- a/pkg/meta/sql_lock.go
+++ b/pkg/meta/sql_lock.go
@@ -60,29 +60,29 @@ func (m *dbMeta) Flock(ctx Context, inode Ino, owner_ uint64, ltype uint32, bloc
 				locks[key{l.Sid, l.Owner}] = l
 			}
 
+			me := key{m.sid, owner}
+			flk, ok := locks[me]
+			delete(locks, me)
+			var typec byte = 'W'
 			if ltype == F_RDLCK {
 				for _, l := range locks {
 					if l.Ltype == 'W' {
 						return syscall.EAGAIN
 					}
 				}
-				return mustInsert(s, flock{Inode: inode, Owner: owner, Ltype: 'R', Sid: m.sid})
-			}
-			me := key{m.sid, owner}
-			flk, ok := locks[me]
-			delete(locks, me)
-			if len(locks) > 0 {
+				typec = 'R'
+			} else if len(locks) > 0 {
 				return syscall.EAGAIN
 			}
 			var n int64
 			if ok {
-				if flk.Ltype != 'W' {
-					n, err = s.Cols("Ltype").Update(&flock{Ltype: 'W'}, &flock{Inode: inode, Owner: owner, Sid: m.sid})
+				if flk.Ltype != typec {
+					n, err = s.Cols("Ltype").Update(&flock{Ltype: typec}, &flock{Inode: inode, Owner: owner, Sid: m.sid})
 				} else {
 					n = 1
 				}
 			} else {
-				n, err = s.InsertOne(&flock{Inode: inode, Owner: owner, Ltype: 'W', Sid: m.sid})
+				n, err = s.InsertOne(&flock{Inode: inode, Owner: owner, Ltype: typec, Sid: m.sid})
 			}
 			if err == nil && n == 0 {
 				err = fmt.Errorf("insert/update failed")
diff --git a/pkg/meta/tkv_lock.go b/pkg/meta/tkv_lock.go
index 8b799fed6f5c..5606a744a1cc 100644
--- a/pkg/meta/tkv_lock.go
+++ b/pkg/meta/tkv_lock.go
@@ -63,8 +63,8 @@ func (m *kvMeta) Flock(ctx Context, inode Ino, owner uint64, ltype uint32, block
 			case F_UNLCK:
 				delete(ls, lkey)
 			case F_RDLCK:
-				for _, l := range ls {
-					if l == 'W' {
+				for o, l := range ls {
+					if l == 'W' && o != lkey {
 						return syscall.EAGAIN
 					}
 				}