8288904: Incorrect memory ordering in UL

jdksjolen · David Holmes · commit 357902415dd6 · 2022-07-30T07:34:39.000Z
Reviewed-by: rehn, dholmes
diff --git a/src/hotspot/share/logging/logOutputList.cpp b/src/hotspot/share/logging/logOutputList.cpp
@@ -43,9 +43,12 @@ jint LogOutputList::decrease_readers() {
 
 void LogOutputList::wait_until_no_readers() const {
   OrderAccess::storeload();
-  while (_active_readers != 0) {
+  while (Atomic::load(&_active_readers) != 0) {
     // Busy wait
   }
+  // Prevent mutations to the output list to float above the active reader check.
+  // Such a reordering would lead to readers loading faulty data.
+  OrderAccess::loadstore();
 }
 
 void LogOutputList::set_output_level(LogOutput* output, LogLevelType level) {

Original file line number	Diff line number	Diff line change
`@@ -43,9 +43,12 @@ jint LogOutputList::decrease_readers() {`
`43`	`43`
`44`	`44`	`void LogOutputList::wait_until_no_readers() const {`
`45`	`45`	`OrderAccess::storeload();`
`46`		`- while (_active_readers != 0) {`
	`46`	`+ while (Atomic::load(&_active_readers) != 0) {`
`47`	`47`	`// Busy wait`
`48`	`48`	`}`
	`49`	`+ // Prevent mutations to the output list to float above the active reader check.`
	`50`	`+ // Such a reordering would lead to readers loading faulty data.`
	`51`	`+ OrderAccess::loadstore();`
`49`	`52`	`}`
`50`	`53`
`51`	`54`	`void LogOutputList::set_output_level(LogOutput* output, LogLevelType level) {`