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(0.42) Prevent requesting exclusive, if already acquired #18629

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Dec 14, 2023
Merged

(0.42) Prevent requesting exclusive, if already acquired #18629

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12 changes: 8 additions & 4 deletions runtime/jvmti/jvmtiClass.c
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Original file line number Diff line number Diff line change
Expand Up @@ -1233,10 +1233,14 @@ redefineClassesCommon(jvmtiEnv* env,
/* Eliminate dark matter so that none will be encountered in prepareToFixMemberNames(). */
UDATA savedAllowUserHeapWalkFlag = vm->requiredDebugAttributes & J9VM_DEBUG_ATTRIBUTE_ALLOW_USER_HEAP_WALK;
vm->requiredDebugAttributes |= J9VM_DEBUG_ATTRIBUTE_ALLOW_USER_HEAP_WALK;
/* J9MMCONSTANT_EXPLICIT_GC_RASDUMP_COMPACT allows the GC to run while the current thread is holding
* exclusive VM access.
*/
vm->memoryManagerFunctions->j9gc_modron_global_collect_with_overrides(currentThread, J9MMCONSTANT_EXPLICIT_GC_RASDUMP_COMPACT);

/* This is to help with Metronome to avoid requesting Exclusive if we already have SafePoint, which may not look as Exclusive to the requester thread */
vm->alreadyHaveExclusive = TRUE;

vm->memoryManagerFunctions->j9gc_modron_global_collect_with_overrides(currentThread, J9MMCONSTANT_EXPLICIT_GC_EXCLUSIVE_VMACCESS_ALREADY_ACQUIRED);

vm->alreadyHaveExclusive = FALSE;

if (0 == savedAllowUserHeapWalkFlag) {
/* Clear the flag to restore its original value. */
vm->requiredDebugAttributes &= ~J9VM_DEBUG_ATTRIBUTE_ALLOW_USER_HEAP_WALK;
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1 change: 1 addition & 0 deletions runtime/oti/j9nonbuilder.h
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Expand Up @@ -5911,6 +5911,7 @@ typedef struct J9JavaVM {
UDATA addModulesCount;
UDATA safePointState;
UDATA safePointResponseCount;
BOOLEAN alreadyHaveExclusive;
struct J9VMRuntimeStateListener vmRuntimeStateListener;
#if defined(J9VM_INTERP_ATOMIC_FREE_JNI_USES_FLUSH)
#if defined(J9UNIX) || defined(AIXPPC)
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25 changes: 24 additions & 1 deletion runtime/vm/VMAccess.cpp
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Expand Up @@ -755,6 +755,11 @@ acquireExclusiveVMAccessFromExternalThread(J9JavaVM * vm)
UDATA vmResponsesExpected = 0;
UDATA jniResponsesExpected = 0;

/* If exclusive has already been acquired, nothing need be done here */
if (vm->alreadyHaveExclusive) {
return;
}

synchronizeRequestsFromExternalThread(vm, TRUE);

/* Post the halt request to all threads */
Expand Down Expand Up @@ -836,6 +841,12 @@ void
releaseExclusiveVMAccessFromExternalThread(J9JavaVM * vm)
{
J9VMThread * currentThread;

/* If exclusive has already been acquired, nothing need be done here */
if (vm->alreadyHaveExclusive) {
return;
}

Assert_VM_true(J9_XACCESS_EXCLUSIVE == vm->exclusiveAccessState);

/* Acquire these monitors in the same order as in allocateVMThread to prevent deadlock */
Expand Down Expand Up @@ -913,6 +924,11 @@ requestExclusiveVMAccessMetronomeTemp(J9JavaVM *vm, UDATA block, UDATA *vmRespon
UDATA jniResponsesExpected = 0;
*gcPriority = J9THREAD_PRIORITY_MAX;

/* If exclusive has already been acquired, nothing need be done here */
if (vm->alreadyHaveExclusive) {
return FALSE;
}

/* Check if another party is requesting X access already. */
if (FALSE == synchronizeRequestsFromExternalThread(vm, block)) {
/* Yes, there was another party requesting X access, but because we did not want to block,
Expand Down Expand Up @@ -1010,7 +1026,14 @@ waitForExclusiveVMAccessMetronome(J9VMThread * vmThread, UDATA responsesRequired
void
waitForExclusiveVMAccessMetronomeTemp(J9VMThread * vmThread, UDATA vmResponsesRequired, UDATA jniResponsesRequired)
{
waitForResponseFromExternalThread(vmThread->javaVM, vmResponsesRequired, jniResponsesRequired);
J9JavaVM *vm = vmThread->javaVM;

/* If exclusive has already been acquired, nothing need be done here */
if (vm->alreadyHaveExclusive) {
return;
}

waitForResponseFromExternalThread(vm, vmResponsesRequired, jniResponsesRequired);

VM_VMAccess::backOffFromSafePoint(vmThread);

Expand Down