diff --git a/src/hotspot/cpu/aarch64/c1_LIRAssembler_aarch64.cpp b/src/hotspot/cpu/aarch64/c1_LIRAssembler_aarch64.cpp
index 5e116d82761ac..1385366d8793b 100644
--- a/src/hotspot/cpu/aarch64/c1_LIRAssembler_aarch64.cpp
+++ b/src/hotspot/cpu/aarch64/c1_LIRAssembler_aarch64.cpp
@@ -1168,8 +1168,8 @@ void LIR_Assembler::emit_opConvert(LIR_OpConvert* op) {
 
 void LIR_Assembler::emit_alloc_obj(LIR_OpAllocObj* op) {
   if (op->init_check()) {
-    __ ldrb(rscratch1, Address(op->klass()->as_register(),
-                               InstanceKlass::init_state_offset()));
+    __ lea(rscratch1, Address(op->klass()->as_register(), InstanceKlass::init_state_offset()));
+    __ ldarb(rscratch1, rscratch1);
     __ cmpw(rscratch1, InstanceKlass::fully_initialized);
     add_debug_info_for_null_check_here(op->stub()->info());
     __ br(Assembler::NE, *op->stub()->entry());
diff --git a/src/hotspot/cpu/aarch64/macroAssembler_aarch64.cpp b/src/hotspot/cpu/aarch64/macroAssembler_aarch64.cpp
index c5c02619d446e..16473b09fff42 100644
--- a/src/hotspot/cpu/aarch64/macroAssembler_aarch64.cpp
+++ b/src/hotspot/cpu/aarch64/macroAssembler_aarch64.cpp
@@ -1838,7 +1838,8 @@ void MacroAssembler::clinit_barrier(Register klass, Register scratch, Label* L_f
     L_slow_path = &L_fallthrough;
   }
   // Fast path check: class is fully initialized
-  ldrb(scratch, Address(klass, InstanceKlass::init_state_offset()));
+  lea(scratch, Address(klass, InstanceKlass::init_state_offset()));
+  ldarb(scratch, scratch);
   subs(zr, scratch, InstanceKlass::fully_initialized);
   br(Assembler::EQ, *L_fast_path);
 
diff --git a/src/hotspot/cpu/arm/c1_LIRAssembler_arm.cpp b/src/hotspot/cpu/arm/c1_LIRAssembler_arm.cpp
index bb6a93e6f8da7..b14e6f0b4ca0c 100644
--- a/src/hotspot/cpu/arm/c1_LIRAssembler_arm.cpp
+++ b/src/hotspot/cpu/arm/c1_LIRAssembler_arm.cpp
@@ -948,6 +948,7 @@ void LIR_Assembler::emit_alloc_obj(LIR_OpAllocObj* op) {
   if (op->init_check()) {
     Register tmp = op->tmp1()->as_register();
     __ ldrb(tmp, Address(op->klass()->as_register(), InstanceKlass::init_state_offset()));
+    __ membar(MacroAssembler::Membar_mask_bits(MacroAssembler::LoadLoad | MacroAssembler::LoadStore), Rtemp);
     add_debug_info_for_null_check_here(op->stub()->info());
     __ cmp(tmp, InstanceKlass::fully_initialized);
     __ b(*op->stub()->entry(), ne);
diff --git a/src/hotspot/cpu/arm/templateTable_arm.cpp b/src/hotspot/cpu/arm/templateTable_arm.cpp
index 80519fd89f426..0974ff1f9a9c3 100644
--- a/src/hotspot/cpu/arm/templateTable_arm.cpp
+++ b/src/hotspot/cpu/arm/templateTable_arm.cpp
@@ -3974,6 +3974,7 @@ void TemplateTable::_new() {
   // make sure klass is initialized
   // make sure klass is fully initialized
   __ ldrb(Rtemp, Address(Rklass, InstanceKlass::init_state_offset()));
+  __ membar(MacroAssembler::Membar_mask_bits(MacroAssembler::LoadLoad | MacroAssembler::LoadStore), Rtemp);
   __ cmp(Rtemp, InstanceKlass::fully_initialized);
   __ b(slow_case, ne);
 
diff --git a/src/hotspot/cpu/ppc/c1_LIRAssembler_ppc.cpp b/src/hotspot/cpu/ppc/c1_LIRAssembler_ppc.cpp
index 42934dc7c3179..684c06614a97a 100644
--- a/src/hotspot/cpu/ppc/c1_LIRAssembler_ppc.cpp
+++ b/src/hotspot/cpu/ppc/c1_LIRAssembler_ppc.cpp
@@ -2274,6 +2274,7 @@ void LIR_Assembler::emit_alloc_obj(LIR_OpAllocObj* op) {
     }
     __ lbz(op->tmp1()->as_register(),
            in_bytes(InstanceKlass::init_state_offset()), op->klass()->as_register());
+    // acquire barrier included in membar_storestore() which follows the allocation immediately.
     __ cmpwi(CCR0, op->tmp1()->as_register(), InstanceKlass::fully_initialized);
     __ bc_far_optimized(Assembler::bcondCRbiIs0, __ bi0(CCR0, Assembler::equal), *op->stub()->entry());
   }
diff --git a/src/hotspot/cpu/ppc/macroAssembler_ppc.cpp b/src/hotspot/cpu/ppc/macroAssembler_ppc.cpp
index 8d8e39b8bbc00..a194c030a6124 100644
--- a/src/hotspot/cpu/ppc/macroAssembler_ppc.cpp
+++ b/src/hotspot/cpu/ppc/macroAssembler_ppc.cpp
@@ -2410,7 +2410,7 @@ void MacroAssembler::verify_secondary_supers_table(Register r_sub_klass,
 void MacroAssembler::clinit_barrier(Register klass, Register thread, Label* L_fast_path, Label* L_slow_path) {
   assert(L_fast_path != nullptr || L_slow_path != nullptr, "at least one is required");
 
-  Label L_fallthrough;
+  Label L_check_thread, L_fallthrough;
   if (L_fast_path == nullptr) {
     L_fast_path = &L_fallthrough;
   } else if (L_slow_path == nullptr) {
@@ -2419,10 +2419,14 @@ void MacroAssembler::clinit_barrier(Register klass, Register thread, Label* L_fa
 
   // Fast path check: class is fully initialized
   lbz(R0, in_bytes(InstanceKlass::init_state_offset()), klass);
+  // acquire by cmp-branch-isync if fully_initialized
   cmpwi(CCR0, R0, InstanceKlass::fully_initialized);
-  beq(CCR0, *L_fast_path);
+  bne(CCR0, L_check_thread);
+  isync();
+  b(*L_fast_path);
 
   // Fast path check: current thread is initializer thread
+  bind(L_check_thread);
   ld(R0, in_bytes(InstanceKlass::init_thread_offset()), klass);
   cmpd(CCR0, thread, R0);
   if (L_slow_path == &L_fallthrough) {
diff --git a/src/hotspot/cpu/riscv/c1_LIRAssembler_riscv.cpp b/src/hotspot/cpu/riscv/c1_LIRAssembler_riscv.cpp
index 940706b0a7376..828f70e4decee 100644
--- a/src/hotspot/cpu/riscv/c1_LIRAssembler_riscv.cpp
+++ b/src/hotspot/cpu/riscv/c1_LIRAssembler_riscv.cpp
@@ -980,6 +980,7 @@ void LIR_Assembler::emit_alloc_obj(LIR_OpAllocObj* op) {
   if (op->init_check()) {
     __ lbu(t0, Address(op->klass()->as_register(),
                        InstanceKlass::init_state_offset()));
+    __ membar(MacroAssembler::LoadLoad | MacroAssembler::LoadStore);
     __ mv(t1, (u1)InstanceKlass::fully_initialized);
     add_debug_info_for_null_check_here(op->stub()->info());
     __ bne(t0, t1, *op->stub()->entry(), /* is_far */ true);
diff --git a/src/hotspot/cpu/riscv/macroAssembler_riscv.cpp b/src/hotspot/cpu/riscv/macroAssembler_riscv.cpp
index 32a446959a246..f9196fef3f517 100644
--- a/src/hotspot/cpu/riscv/macroAssembler_riscv.cpp
+++ b/src/hotspot/cpu/riscv/macroAssembler_riscv.cpp
@@ -493,6 +493,7 @@ void MacroAssembler::clinit_barrier(Register klass, Register tmp, Label* L_fast_
 
   // Fast path check: class is fully initialized
   lbu(tmp, Address(klass, InstanceKlass::init_state_offset()));
+  membar(MacroAssembler::LoadLoad | MacroAssembler::LoadStore);
   sub(tmp, tmp, InstanceKlass::fully_initialized);
   beqz(tmp, *L_fast_path);
 
diff --git a/src/hotspot/cpu/s390/c1_LIRAssembler_s390.cpp b/src/hotspot/cpu/s390/c1_LIRAssembler_s390.cpp
index d288f4a893d0a..8990cf1663dd5 100644
--- a/src/hotspot/cpu/s390/c1_LIRAssembler_s390.cpp
+++ b/src/hotspot/cpu/s390/c1_LIRAssembler_s390.cpp
@@ -2350,6 +2350,7 @@ void LIR_Assembler::shift_op(LIR_Code code, LIR_Opr left, jint count, LIR_Opr de
 void LIR_Assembler::emit_alloc_obj(LIR_OpAllocObj* op) {
   if (op->init_check()) {
     // Make sure klass is initialized & doesn't have finalizer.
+    // init_state needs acquire, but S390 is TSO, and so we are already good.
     const int state_offset = in_bytes(InstanceKlass::init_state_offset());
     Register iklass = op->klass()->as_register();
     add_debug_info_for_null_check_here(op->stub()->info());
diff --git a/src/hotspot/cpu/s390/macroAssembler_s390.cpp b/src/hotspot/cpu/s390/macroAssembler_s390.cpp
index af281345b1477..aaa0e1bff8c7d 100644
--- a/src/hotspot/cpu/s390/macroAssembler_s390.cpp
+++ b/src/hotspot/cpu/s390/macroAssembler_s390.cpp
@@ -3458,7 +3458,8 @@ void MacroAssembler::clinit_barrier(Register klass, Register thread, Label* L_fa
     L_slow_path = &L_fallthrough;
   }
 
-  // Fast path check: class is fully initialized
+  // Fast path check: class is fully initialized.
+  // init_state needs acquire, but S390 is TSO, and so we are already good.
   z_cli(Address(klass, InstanceKlass::init_state_offset()), InstanceKlass::fully_initialized);
   z_bre(*L_fast_path);
 
diff --git a/src/hotspot/cpu/x86/c1_LIRAssembler_x86.cpp b/src/hotspot/cpu/x86/c1_LIRAssembler_x86.cpp
index c3444d5a5abce..6d9812c11ae6e 100644
--- a/src/hotspot/cpu/x86/c1_LIRAssembler_x86.cpp
+++ b/src/hotspot/cpu/x86/c1_LIRAssembler_x86.cpp
@@ -1578,6 +1578,7 @@ void LIR_Assembler::emit_opConvert(LIR_OpConvert* op) {
 void LIR_Assembler::emit_alloc_obj(LIR_OpAllocObj* op) {
   if (op->init_check()) {
     add_debug_info_for_null_check_here(op->stub()->info());
+    // init_state needs acquire, but x86 is TSO, and so we are already good.
     __ cmpb(Address(op->klass()->as_register(),
                     InstanceKlass::init_state_offset()),
                     InstanceKlass::fully_initialized);
diff --git a/src/hotspot/cpu/x86/macroAssembler_x86.cpp b/src/hotspot/cpu/x86/macroAssembler_x86.cpp
index 893ae4e844ba4..018258a012e57 100644
--- a/src/hotspot/cpu/x86/macroAssembler_x86.cpp
+++ b/src/hotspot/cpu/x86/macroAssembler_x86.cpp
@@ -5084,7 +5084,8 @@ void MacroAssembler::clinit_barrier(Register klass, Register thread, Label* L_fa
     L_slow_path = &L_fallthrough;
   }
 
-  // Fast path check: class is fully initialized
+  // Fast path check: class is fully initialized.
+  // init_state needs acquire, but x86 is TSO, and so we are already good.
   cmpb(Address(klass, InstanceKlass::init_state_offset()), InstanceKlass::fully_initialized);
   jcc(Assembler::equal, *L_fast_path);
 
diff --git a/src/hotspot/cpu/x86/templateTable_x86.cpp b/src/hotspot/cpu/x86/templateTable_x86.cpp
index 5e783225fcbfc..527d961259ecc 100644
--- a/src/hotspot/cpu/x86/templateTable_x86.cpp
+++ b/src/hotspot/cpu/x86/templateTable_x86.cpp
@@ -4048,6 +4048,7 @@ void TemplateTable::_new() {
   __ push(rcx);  // save the contexts of klass for initializing the header
 
   // make sure klass is initialized
+  // init_state needs acquire, but x86 is TSO, and so we are already good.
 #ifdef _LP64
   assert(VM_Version::supports_fast_class_init_checks(), "must support fast class initialization checks");
   __ clinit_barrier(rcx, r15_thread, nullptr /*L_fast_path*/, &slow_case);
diff --git a/src/hotspot/share/oops/instanceKlass.cpp b/src/hotspot/share/oops/instanceKlass.cpp
index 5e226a90764ee..6b6d35ee026de 100644
--- a/src/hotspot/share/oops/instanceKlass.cpp
+++ b/src/hotspot/share/oops/instanceKlass.cpp
@@ -4103,7 +4103,7 @@ void InstanceKlass::set_init_state(ClassState state) {
   assert(good_state || state == allocated, "illegal state transition");
 #endif
   assert(_init_thread == nullptr, "should be cleared before state change");
-  _init_state = state;
+  Atomic::release_store(&_init_state, state);
 }
 
 #if INCLUDE_JVMTI
diff --git a/src/hotspot/share/oops/instanceKlass.hpp b/src/hotspot/share/oops/instanceKlass.hpp
index eaffa0250d133..45d65f273c866 100644
--- a/src/hotspot/share/oops/instanceKlass.hpp
+++ b/src/hotspot/share/oops/instanceKlass.hpp
@@ -507,14 +507,14 @@ class InstanceKlass: public Klass {
 
  public:
   // initialization state
-  bool is_loaded() const                   { return _init_state >= loaded; }
-  bool is_linked() const                   { return _init_state >= linked; }
-  bool is_initialized() const              { return _init_state == fully_initialized; }
-  bool is_not_initialized() const          { return _init_state <  being_initialized; }
-  bool is_being_initialized() const        { return _init_state == being_initialized; }
-  bool is_in_error_state() const           { return _init_state == initialization_error; }
+  bool is_loaded() const                   { return init_state() >= loaded; }
+  bool is_linked() const                   { return init_state() >= linked; }
+  bool is_initialized() const              { return init_state() == fully_initialized; }
+  bool is_not_initialized() const          { return init_state() <  being_initialized; }
+  bool is_being_initialized() const        { return init_state() == being_initialized; }
+  bool is_in_error_state() const           { return init_state() == initialization_error; }
   bool is_reentrant_initialization(Thread *thread)  { return thread == _init_thread; }
-  ClassState  init_state() const           { return _init_state; }
+  ClassState  init_state() const           { return Atomic::load_acquire(&_init_state); }
   const char* init_state_name() const;
   bool is_rewritten() const                { return _misc_flags.rewritten(); }
 
diff --git a/src/hotspot/share/opto/graphKit.cpp b/src/hotspot/share/opto/graphKit.cpp
index 3bc5b9a8b2a7d..1a0d0bd037515 100644
--- a/src/hotspot/share/opto/graphKit.cpp
+++ b/src/hotspot/share/opto/graphKit.cpp
@@ -3008,7 +3008,7 @@ void GraphKit::guard_klass_being_initialized(Node* klass) {
   Node* adr = basic_plus_adr(top(), klass, init_state_off);
   Node* init_state = LoadNode::make(_gvn, nullptr, immutable_memory(), adr,
                                     adr->bottom_type()->is_ptr(), TypeInt::BYTE,
-                                    T_BYTE, MemNode::unordered);
+                                    T_BYTE, MemNode::acquire);
   init_state = _gvn.transform(init_state);
 
   Node* being_initialized_state = makecon(TypeInt::make(InstanceKlass::being_initialized));
diff --git a/src/hotspot/share/opto/library_call.cpp b/src/hotspot/share/opto/library_call.cpp
index 8bbb2f8115ec4..5dce40ba31d90 100644
--- a/src/hotspot/share/opto/library_call.cpp
+++ b/src/hotspot/share/opto/library_call.cpp
@@ -2899,7 +2899,7 @@ bool LibraryCallKit::inline_unsafe_allocate() {
     Node* insp = basic_plus_adr(kls, in_bytes(InstanceKlass::init_state_offset()));
     // Use T_BOOLEAN for InstanceKlass::_init_state so the compiler
     // can generate code to load it as unsigned byte.
-    Node* inst = make_load(nullptr, insp, TypeInt::UBYTE, T_BOOLEAN, MemNode::unordered);
+    Node* inst = make_load(nullptr, insp, TypeInt::UBYTE, T_BOOLEAN, MemNode::acquire);
     Node* bits = intcon(InstanceKlass::fully_initialized);
     test = _gvn.transform(new SubINode(inst, bits));
     // The 'test' is non-zero if we need to take a slow path.