variable: fix data race in the variable.SetPDClientDynamicOption (#38374

)

close #38373

br/pkg/restore/BUILD.bazel

@@ -111,6 +111,8 @@ go_test(
     ],
     embed = [":restore"],
     flaky = True,
+    race = "on",
+    shard_count = 20,
     deps = [
         "//br/pkg/backup",
         "//br/pkg/conn",

domain/domain_sysvars.go

@@ -31,7 +31,8 @@ import (
 // which is overwritten here.
 func (do *Domain) initDomainSysVars() {
 	variable.SetStatsCacheCapacity.Store(do.setStatsCacheCapacity)
-	variable.SetPDClientDynamicOption = do.setPDClientDynamicOption
+	pdClientDynamicOptionFunc := do.setPDClientDynamicOption
+	variable.SetPDClientDynamicOption.Store(&pdClientDynamicOptionFunc)
 }
 
 // setStatsCacheCapacity sets statsCache cap

sessionctx/variable/sysvar.go

@@ -496,13 +496,13 @@ var defaultSysVars = []*SysVar{
 			return strconv.FormatFloat(MaxTSOBatchWaitInterval.Load(), 'f', -1, 64), nil
 		},
 		SetGlobal: func(s *SessionVars, val string) error {
-			SetPDClientDynamicOption(TiDBTSOClientBatchMaxWaitTime, val)
+			(*SetPDClientDynamicOption.Load())(TiDBTSOClientBatchMaxWaitTime, val)
 			return nil
 		}},
 	{Scope: ScopeGlobal, Name: TiDBEnableTSOFollowerProxy, Value: BoolToOnOff(DefTiDBEnableTSOFollowerProxy), Type: TypeBool, GetGlobal: func(sv *SessionVars) (string, error) {
 		return BoolToOnOff(EnableTSOFollowerProxy.Load()), nil
 	}, SetGlobal: func(s *SessionVars, val string) error {
-		SetPDClientDynamicOption(TiDBEnableTSOFollowerProxy, val)
+		(*SetPDClientDynamicOption.Load())(TiDBEnableTSOFollowerProxy, val)
 		return nil
 	}},
 	{Scope: ScopeGlobal, Name: TiDBEnableLocalTxn, Value: BoolToOnOff(DefTiDBEnableLocalTxn), Hidden: true, Type: TypeBool, GetGlobal: func(sv *SessionVars) (string, error) {

sessionctx/variable/tidb_vars.go

@@ -1117,7 +1117,7 @@ var (
 	// SetStatsCacheCapacity is the func registered by domain to set statsCache memory quota.
 	SetStatsCacheCapacity atomic.Value
 	// SetPDClientDynamicOption is the func registered by domain
-	SetPDClientDynamicOption func(string, string) = nil
+	SetPDClientDynamicOption atomic.Pointer[func(string, string)]
 	// SwitchConcurrentDDL is the func registered by DDL to switch concurrent DDL.
 	SwitchConcurrentDDL func(bool) error = nil
 	// SwitchMDL is the func registered by DDL to switch MDL.