8219586: CodeHeap State Analytics processes dead nmethods

Reviewed-by: thartmann, eosterlund

Author: RealLucy

src/hotspot/share/code/codeBlob.cpp

@@ -99,6 +99,7 @@ CodeBlob::CodeBlob(const char* name, CompilerType type, const CodeBlobLayout& la
   // probably wrong for tiered
   assert(_frame_size >= -1, "must use frame size or -1 for runtime stubs");
 #endif // COMPILER1
+  S390_ONLY(_ctable_offset = 0;) // avoid uninitialized fields
 }
 
 CodeBlob::CodeBlob(const char* name, CompilerType type, const CodeBlobLayout& layout, CodeBuffer* cb, int frame_complete_offset, int frame_size, OopMapSet* oop_maps, bool caller_must_gc_arguments) :
@@ -128,6 +129,7 @@ CodeBlob::CodeBlob(const char* name, CompilerType type, const CodeBlobLayout& la
   // probably wrong for tiered
   assert(_frame_size >= -1, "must use frame size or -1 for runtime stubs");
 #endif // COMPILER1
+  S390_ONLY(_ctable_offset = 0;) // avoid uninitialized fields
 }
 
 

src/hotspot/share/code/codeHeapState.cpp

@@ -47,6 +47,8 @@ class CodeHeapState : public CHeapObj<mtCode> {
     // The nMethod_* values correspond to the CompiledMethod enum values.
     // We can't use the CompiledMethod values 1:1 because we depend on noType == 0.
     nMethod_inconstruction, // under construction. Very soon, the type will transition to "in_use".
+                            // can't be observed while holding Compile_lock and CodeCache_lock simultaneously.
+                            // left in here for completeness (and to document we spent a thought).
     nMethod_inuse,          // executable. This is the "normal" state for a nmethod.
     nMethod_notused,        // assumed inactive, marked not entrant. Could be revived if necessary.
     nMethod_notentrant,     // no new activations allowed, marked for deoptimization. Old activations may still exist.
@@ -95,7 +97,9 @@ class CodeHeapState : public CHeapObj<mtCode> {
   static void print_line_delim(outputStream* out, bufferedStream *sst, char* low_bound, unsigned int ix, unsigned int gpl);
   static void print_line_delim(outputStream* out, outputStream *sst, char* low_bound, unsigned int ix, unsigned int gpl);
   static blobType get_cbType(CodeBlob* cb);
-  static bool blob_access_is_safe(CodeBlob* this_blob, CodeBlob* prev_blob);
+  static bool blob_access_is_safe(CodeBlob* this_blob);
+  static bool nmethod_access_is_safe(nmethod* nm);
+  static bool holding_required_locks();
 
  public:
   static void discard(outputStream* out, CodeHeap* heap);
@@ -164,12 +168,16 @@ struct FreeBlk : public CHeapObj<mtCode> {
 //  know about those largest blocks.
 //  All TopSizeBlks of a heap segment are stored in the related TopSizeArray.
 struct TopSizeBlk : public CHeapObj<mtCode> {
-  HeapBlock*     start;       // address of block
+  HeapBlock*     start;        // address of block
+  const char*    blob_name;    // name of blob (mostly: name_and_sig of nmethod)
   unsigned int   len;          // length of block, in _segment_size units. Will never overflow int.
 
   unsigned int   index;        // ordering index, 0 is largest block
                                // contains array index of next smaller block
                                // -1 indicates end of list
+
+  unsigned int   nm_size;      // nmeethod total size (if nmethod, 0 otherwise)
+  int            temperature;  // nmethod temperature (if nmethod, 0 otherwise)
   CompLevel      level;        // optimization level (see globalDefinitions.hpp)
   u2             compiler;     // compiler which generated this blob
   u2             type;         // blob type
@@ -216,7 +224,6 @@ struct CodeHeapStat {
     unsigned int  nBlocks_t2;
     unsigned int  nBlocks_alive;
     unsigned int  nBlocks_dead;
-    unsigned int  nBlocks_inconstr;
     unsigned int  nBlocks_unloaded;
     unsigned int  nBlocks_stub;
     // FreeBlk data

src/hotspot/share/code/codeHeapState.hpp

@@ -69,6 +69,13 @@ CompiledMethod::CompiledMethod(Method* method, const char* name, CompilerType ty
 }
 
 void CompiledMethod::init_defaults() {
+  { // avoid uninitialized fields, even for short time periods
+    _is_far_code                = false;
+    _scopes_data_begin          = NULL;
+    _deopt_handler_begin        = NULL;
+    _deopt_mh_handler_begin     = NULL;
+    _exception_cache            = NULL;
+  }
   _has_unsafe_access          = 0;
   _has_method_handle_invokes  = 0;
   _lazy_critical_native       = 0;
@@ -692,21 +699,6 @@ bool CompiledMethod::cleanup_inline_caches_impl(bool unloading_occurred, bool cl
   return true;
 }
 
-// Iterating over all nmethods, e.g. with the help of CodeCache::nmethods_do(fun) was found
-// to not be inherently safe. There is a chance that fields are seen which are not properly
-// initialized. This happens despite the fact that nmethods_do() asserts the CodeCache_lock
-// to be held.
-// To bundle knowledge about necessary checks in one place, this function was introduced.
-// It is not claimed that these checks are sufficient, but they were found to be necessary.
-bool CompiledMethod::nmethod_access_is_safe(nmethod* nm) {
-  Method* method = (nm == NULL) ? NULL : nm->method();  // nm->method() may be uninitialized, i.e. != NULL, but invalid
-  return (nm != NULL) && (method != NULL) && (method->signature() != NULL) &&
-         !nm->is_zombie() && !nm->is_not_installed() &&
-         os::is_readable_pointer(method) &&
-         os::is_readable_pointer(method->constants()) &&
-         os::is_readable_pointer(method->signature());
-}
-
 address CompiledMethod::continuation_for_implicit_exception(address pc, bool for_div0_check) {
   // Exception happened outside inline-cache check code => we are inside
   // an active nmethod => use cpc to determine a return address

src/hotspot/share/code/compiledMethod.cpp

@@ -254,8 +254,6 @@ class CompiledMethod : public CodeBlob {
     return _mark_for_deoptimization_status != deoptimize_noupdate;
   }
 
-  static bool nmethod_access_is_safe(nmethod* nm);
-
   // tells whether frames described by this nmethod can be deoptimized
   // note: native wrappers cannot be deoptimized.
   bool can_be_deoptimized() const { return is_java_method(); }

src/hotspot/share/code/compiledMethod.hpp

@@ -2764,42 +2764,59 @@ void CompileBroker::print_heapinfo(outputStream* out, const char* function, size
   }
 
   // We hold the CodeHeapStateAnalytics_lock all the time, from here until we leave this function.
-  // That prevents another thread from destroying our view on the CodeHeap.
+  // That prevents other threads from destroying (making inconsistent) our view on the CodeHeap.
   // When we request individual parts of the analysis via the jcmd interface, it is possible
   // that in between another thread (another jcmd user or the vm running into CodeCache OOM)
-  // updated the aggregated data. That's a tolerable tradeoff because we can't hold a lock
-  // across user interaction.
-  // Acquire this lock before acquiring the CodeCache_lock.
-  // CodeHeapStateAnalytics_lock could be held by a concurrent thread for a long time,
-  // leading to an unnecessarily long hold time of the CodeCache_lock.
+  // updated the aggregated data. We will then see a modified, but again consistent, view
+  // on the CodeHeap. That's a tolerable tradeoff we have to accept because we can't hold
+  // a lock across user interaction.
+
+  // We should definitely acquire this lock before acquiring Compile_lock and CodeCache_lock.
+  // CodeHeapStateAnalytics_lock may be held by a concurrent thread for a long time,
+  // leading to an unnecessarily long hold time of the other locks we acquired before.
   ts.update(); // record starting point
-  MutexLocker mu1(CodeHeapStateAnalytics_lock, Mutex::_no_safepoint_check_flag);
+  MutexLocker mu0(CodeHeapStateAnalytics_lock, Mutex::_safepoint_check_flag);
   out->print_cr("\n__ CodeHeapStateAnalytics lock wait took %10.3f seconds _________\n", ts.seconds());
 
-  // If we serve an "allFun" call, it is beneficial to hold the CodeCache_lock
-  // for the entire duration of aggregation and printing. That makes sure
-  // we see a consistent picture and do not run into issues caused by
-  // the CodeHeap being altered concurrently.
-  Mutex* global_lock   = allFun ? CodeCache_lock : NULL;
-  Mutex* function_lock = allFun ? NULL : CodeCache_lock;
+  // Holding the CodeCache_lock protects from concurrent alterations of the CodeCache.
+  // Unfortunately, such protection is not sufficient:
+  // When a new nmethod is created via ciEnv::register_method(), the
+  // Compile_lock is taken first. After some initializations,
+  // nmethod::new_nmethod() takes over, grabbing the CodeCache_lock
+  // immediately (after finalizing the oop references). To lock out concurrent
+  // modifiers, we have to grab both locks as well in the described sequence.
+  //
+  // If we serve an "allFun" call, it is beneficial to hold CodeCache_lock and Compile_lock
+  // for the entire duration of aggregation and printing. That makes sure we see
+  // a consistent picture and do not run into issues caused by concurrent alterations.
+  bool should_take_Compile_lock   = !SafepointSynchronize::is_at_safepoint() &&
+                                    !Compile_lock->owned_by_self();
+  bool should_take_CodeCache_lock = !SafepointSynchronize::is_at_safepoint() &&
+                                    !CodeCache_lock->owned_by_self();
+  Mutex*   global_lock_1   = allFun ? (should_take_Compile_lock   ? Compile_lock   : NULL) : NULL;
+  Monitor* global_lock_2   = allFun ? (should_take_CodeCache_lock ? CodeCache_lock : NULL) : NULL;
+  Mutex*   function_lock_1 = allFun ? NULL : (should_take_Compile_lock   ? Compile_lock    : NULL);
+  Monitor* function_lock_2 = allFun ? NULL : (should_take_CodeCache_lock ? CodeCache_lock  : NULL);
   ts_global.update(); // record starting point
-  MutexLocker mu2(global_lock, Mutex::_no_safepoint_check_flag);
-  if (global_lock != NULL) {
-    out->print_cr("\n__ CodeCache (global) lock wait took %10.3f seconds _________\n", ts_global.seconds());
+  MutexLocker mu1(global_lock_1, Mutex::_safepoint_check_flag);
+  MutexLocker mu2(global_lock_2, Mutex::_no_safepoint_check_flag);
+  if ((global_lock_1 != NULL) || (global_lock_2 != NULL)) {
+    out->print_cr("\n__ Compile & CodeCache (global) lock wait took %10.3f seconds _________\n", ts_global.seconds());
     ts_global.update(); // record starting point
   }
 
   if (aggregate) {
     ts.update(); // record starting point
-    MutexLocker mu3(function_lock, Mutex::_no_safepoint_check_flag);
-    if (function_lock != NULL) {
-      out->print_cr("\n__ CodeCache (function) lock wait took %10.3f seconds _________\n", ts.seconds());
+    MutexLocker mu11(function_lock_1, Mutex::_safepoint_check_flag);
+    MutexLocker mu22(function_lock_2, Mutex::_no_safepoint_check_flag);
+    if ((function_lock_1 != NULL) || (function_lock_1 != NULL)) {
+      out->print_cr("\n__ Compile & CodeCache (function) lock wait took %10.3f seconds _________\n", ts.seconds());
     }
 
     ts.update(); // record starting point
     CodeCache::aggregate(out, granularity);
-    if (function_lock != NULL) {
-      out->print_cr("\n__ CodeCache (function) lock hold took %10.3f seconds _________\n", ts.seconds());
+    if ((function_lock_1 != NULL) || (function_lock_1 != NULL)) {
+      out->print_cr("\n__ Compile & CodeCache (function) lock hold took %10.3f seconds _________\n", ts.seconds());
     }
   }
 
@@ -2809,15 +2826,18 @@ void CompileBroker::print_heapinfo(outputStream* out, const char* function, size
   if (methodSpace) CodeCache::print_space(out);
   if (methodAge) CodeCache::print_age(out);
   if (methodNames) {
-    // print_names() has shown to be sensitive to concurrent CodeHeap modifications.
-    // Therefore, request  the CodeCache_lock before calling...
-    MutexLocker mu3(function_lock, Mutex::_no_safepoint_check_flag);
-    CodeCache::print_names(out);
+    if (allFun) {
+      // print_names() can only be used safely if the locks have been continuously held
+      // since aggregation begin. That is true only for function "all".
+      CodeCache::print_names(out);
+    } else {
+      out->print_cr("\nCodeHeapStateAnalytics: Function 'MethodNames' is only available as part of function 'all'");
+    }
   }
   if (discard) CodeCache::discard(out);
 
-  if (global_lock != NULL) {
-    out->print_cr("\n__ CodeCache (global) lock hold took %10.3f seconds _________\n", ts_global.seconds());
+  if ((global_lock_1 != NULL) || (global_lock_2 != NULL)) {
+    out->print_cr("\n__ Compile & CodeCache (global) lock hold took %10.3f seconds _________\n", ts_global.seconds());
   }
   out->print_cr("\n__ CodeHeapStateAnalytics total duration %10.3f seconds _________\n", ts_total.seconds());
 }

src/hotspot/share/compiler/compileBroker.cpp

@@ -205,6 +205,7 @@ bool CodeHeap::reserve(ReservedSpace rs, size_t committed_size, size_t segment_s
   assert(rs.size() >= committed_size, "reserved < committed");
   assert(segment_size >= sizeof(FreeBlock), "segment size is too small");
   assert(is_power_of_2(segment_size), "segment_size must be a power of 2");
+  assert_locked_or_safepoint(CodeCache_lock);
 
   _segment_size      = segment_size;
   _log2_segment_size = exact_log2(segment_size);
@@ -253,6 +254,8 @@ bool CodeHeap::reserve(ReservedSpace rs, size_t committed_size, size_t segment_s
 
 
 bool CodeHeap::expand_by(size_t size) {
+  assert_locked_or_safepoint(CodeCache_lock);
+
   // expand _memory space
   size_t dm = align_to_page_size(_memory.committed_size() + size) - _memory.committed_size();
   if (dm > 0) {
@@ -283,6 +286,7 @@ bool CodeHeap::expand_by(size_t size) {
 void* CodeHeap::allocate(size_t instance_size) {
   size_t number_of_segments = size_to_segments(instance_size + header_size());
   assert(segments_to_size(number_of_segments) >= sizeof(FreeBlock), "not enough room for FreeList");
+  assert_locked_or_safepoint(CodeCache_lock);
 
   // First check if we can satisfy request from freelist
   NOT_PRODUCT(verify());
@@ -347,6 +351,8 @@ HeapBlock* CodeHeap::split_block(HeapBlock *b, size_t split_at) {
 
 void CodeHeap::deallocate_tail(void* p, size_t used_size) {
   assert(p == find_start(p), "illegal deallocation");
+  assert_locked_or_safepoint(CodeCache_lock);
+
   // Find start of HeapBlock
   HeapBlock* b = (((HeapBlock *)p) - 1);
   assert(b->allocated_space() == p, "sanity check");
@@ -363,6 +369,8 @@ void CodeHeap::deallocate_tail(void* p, size_t used_size) {
 
 void CodeHeap::deallocate(void* p) {
   assert(p == find_start(p), "illegal deallocation");
+  assert_locked_or_safepoint(CodeCache_lock);
+
   // Find start of HeapBlock
   HeapBlock* b = (((HeapBlock *)p) - 1);
   assert(b->allocated_space() == p, "sanity check");
@@ -790,6 +798,7 @@ void CodeHeap::print() {
 
 void CodeHeap::verify() {
   if (VerifyCodeCache) {
+    assert_locked_or_safepoint(CodeCache_lock);
     size_t len = 0;
     int count = 0;
     for(FreeBlock* b = _freelist; b != NULL; b = b->link()) {

src/hotspot/share/memory/heap.cpp

@@ -332,7 +332,7 @@ void mutex_init() {
   def(UnsafeJlong_lock             , PaddedMutex  , special,     false, _safepoint_check_never);
 #endif
 
-  def(CodeHeapStateAnalytics_lock  , PaddedMutex  , leaf,        true,  _safepoint_check_never);
+  def(CodeHeapStateAnalytics_lock  , PaddedMutex  , nonleaf+6,   false, _safepoint_check_always);
   def(NMethodSweeperStats_lock     , PaddedMutex  , special,     true,  _safepoint_check_never);
   def(ThreadsSMRDelete_lock        , PaddedMonitor, special,     true,  _safepoint_check_never);
   def(ThreadIdTableCreate_lock     , PaddedMutex  , leaf,        false, _safepoint_check_always);