1 /*
  2  * Copyright (c) 1998, 2025, Oracle and/or its affiliates. All rights reserved.
  3  * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
  4  *
  5  * This code is free software; you can redistribute it and/or modify it
  6  * under the terms of the GNU General Public License version 2 only, as
  7  * published by the Free Software Foundation.
  8  *
  9  * This code is distributed in the hope that it will be useful, but WITHOUT
 10  * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
 11  * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
 12  * version 2 for more details (a copy is included in the LICENSE file that
 13  * accompanied this code).
 14  *
 15  * You should have received a copy of the GNU General Public License version
 16  * 2 along with this work; if not, write to the Free Software Foundation,
 17  * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
 18  *
 19  * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
 20  * or visit www.oracle.com if you need additional information or have any
 21  * questions.
 22  *
 23  */
 24 
 25 #include "logging/log.hpp"
 26 #include "memory/resourceArea.hpp"
 27 #include "runtime/interfaceSupport.inline.hpp"
 28 #include "runtime/javaThread.inline.hpp"
 29 #include "runtime/mutex.hpp"
 30 #include "runtime/os.inline.hpp"
 31 #include "runtime/osThread.hpp"
 32 #include "runtime/safepointMechanism.inline.hpp"
 33 #include "runtime/semaphore.inline.hpp"
 34 #include "runtime/threadCrashProtection.hpp"
 35 #include "utilities/events.hpp"
 36 #include "utilities/macros.hpp"
 37 
 38 class InFlightMutexRelease {
 39  private:
 40   Mutex* _in_flight_mutex;
 41  public:
 42   InFlightMutexRelease(Mutex* in_flight_mutex) : _in_flight_mutex(in_flight_mutex) {
 43     assert(in_flight_mutex != nullptr, "must be");
 44   }
 45   void operator()(JavaThread* current) {
 46     _in_flight_mutex->release_for_safepoint();
 47     _in_flight_mutex = nullptr;
 48   }
 49   bool not_released() { return _in_flight_mutex != nullptr; }
 50 };
 51 
 52 #ifdef ASSERT
 53 void Mutex::check_block_state(Thread* thread) {
 54   if (!_allow_vm_block && thread->is_VM_thread()) {
 55     // JavaThreads are checked to make sure that they do not hold _allow_vm_block locks during operations
 56     // that could safepoint.  Make sure the vm thread never uses locks with _allow_vm_block == false.
 57     fatal("VM thread could block on lock that may be held by a JavaThread during safepoint: %s", name());
 58   }
 59 
 60   assert(!ThreadCrashProtection::is_crash_protected(thread),
 61          "locking not allowed when crash protection is set");
 62 }
 63 
 64 void Mutex::check_safepoint_state(Thread* thread) {
 65   check_block_state(thread);
 66 
 67   // If the lock acquisition checks for safepoint, verify that the lock was created with rank that
 68   // has safepoint checks. Technically this doesn't affect NonJavaThreads since they won't actually
 69   // check for safepoint, but let's make the rule unconditional unless there's a good reason not to.
 70   assert(_rank > nosafepoint,
 71          "This lock should not be taken with a safepoint check: %s", name());
 72 
 73   if (thread->is_active_Java_thread()) {
 74     // Also check NoSafepointVerifier, and thread state is _thread_in_vm
 75     JavaThread::cast(thread)->check_for_valid_safepoint_state();
 76   }
 77 }
 78 
 79 void Mutex::check_no_safepoint_state(Thread* thread) {
 80   check_block_state(thread);
 81   assert(!thread->is_active_Java_thread() || _rank <= nosafepoint,
 82          "This lock should always have a safepoint check for Java threads: %s",
 83          name());
 84 }
 85 #endif // ASSERT
 86 
 87 void Mutex::lock_contended(Thread* self) {
 88   DEBUG_ONLY(int retry_cnt = 0;)
 89   bool is_active_Java_thread = self->is_active_Java_thread();
 90   do {
 91     #ifdef ASSERT
 92     if (retry_cnt++ > 3) {
 93       log_trace(vmmutex)("JavaThread " INTPTR_FORMAT " on %d attempt trying to acquire vmmutex %s", p2i(self), retry_cnt, _name);
 94     }
 95     #endif // ASSERT
 96 
 97     // Is it a JavaThread participating in the safepoint protocol.
 98     if (is_active_Java_thread) {
 99       InFlightMutexRelease ifmr(this);
100       assert(rank() > Mutex::nosafepoint, "Potential deadlock with nosafepoint or lesser rank mutex");
101       {
102         ThreadBlockInVMPreprocess<InFlightMutexRelease> tbivmdc(JavaThread::cast(self), ifmr);
103         _lock.lock();
104       }
105       if (ifmr.not_released()) {
106         // Not unlocked by ~ThreadBlockInVMPreprocess
107         break;
108       }
109     } else {
110       _lock.lock();
111       break;
112     }
113   } while (!_lock.try_lock());
114 }
115 
116 void Mutex::lock(Thread* self) {
117   assert(owner() != self, "invariant");
118 
119   check_safepoint_state(self);
120   check_rank(self);
121 
122   OrderAccess::fence();
123   if (!_lock.try_lock()) {
124     // The lock is contended, use contended slow-path function to lock
125     lock_contended(self);
126   }
127 
128   assert_owner(nullptr);
129   set_owner(self);
130 }
131 
132 void Mutex::lock() {
133   lock(Thread::current());
134 }
135 
136 // Lock without safepoint check - a degenerate variant of lock() for use by
137 // JavaThreads when it is known to be safe to not check for a safepoint when
138 // acquiring this lock. If the thread blocks acquiring the lock it is not
139 // safepoint-safe and so will prevent a safepoint from being reached. If used
140 // in the wrong way this can lead to a deadlock with the safepoint code.
141 
142 void Mutex::lock_without_safepoint_check(Thread * self) {
143   assert(owner() != self, "invariant");
144 
145   check_no_safepoint_state(self);
146   check_rank(self);
147 
148   OrderAccess::fence();
149   _lock.lock();
150   assert_owner(nullptr);
151   set_owner(self);
152 }
153 
154 void Mutex::lock_without_safepoint_check() {
155   lock_without_safepoint_check(Thread::current());
156 }
157 
158 
159 // Returns true if thread succeeds in grabbing the lock, otherwise false.
160 bool Mutex::try_lock_inner(bool do_rank_checks) {
161   Thread * const self = Thread::current();
162   // Checking the owner hides the potential difference in recursive locking behaviour
163   // on some platforms.
164   if (owner() == self) {
165     return false;
166   }
167 
168   if (do_rank_checks) {
169     check_rank(self);
170   }
171   // Some safepoint checking locks use try_lock, so cannot check
172   // safepoint state, but can check blocking state.
173   check_block_state(self);
174 
175   OrderAccess::fence();
176   if (_lock.try_lock()) {
177     assert_owner(nullptr);
178     set_owner(self);
179     return true;
180   }
181   return false;
182 }
183 
184 bool Mutex::try_lock() {
185   return try_lock_inner(true /* do_rank_checks */);
186 }
187 
188 bool Mutex::try_lock_without_rank_check() {
189   bool res = try_lock_inner(false /* do_rank_checks */);
190   DEBUG_ONLY(if (res) _skip_rank_check = true;)
191   return res;
192 }
193 
194 void Mutex::release_for_safepoint() {
195   assert_owner(nullptr);
196   _lock.unlock();
197 }
198 
199 void Mutex::unlock() {
200   DEBUG_ONLY(assert_owner(Thread::current()));
201   set_owner(nullptr);
202   _lock.unlock();
203 }
204 
205 void Monitor::notify() {
206   DEBUG_ONLY(assert_owner(Thread::current()));
207   _lock.notify();
208 }
209 
210 void Monitor::notify_all() {
211   DEBUG_ONLY(assert_owner(Thread::current()));
212   _lock.notify_all();
213 }
214 
215 // timeout is in milliseconds - with zero meaning never timeout
216 bool Monitor::wait_without_safepoint_check(uint64_t timeout) {
217   Thread* const self = Thread::current();
218 
219   assert_owner(self);
220   check_rank(self);
221 
222   // conceptually set the owner to null in anticipation of
223   // abdicating the lock in wait
224   set_owner(nullptr);
225 
226   // Check safepoint state after resetting owner and possible NSV.
227   check_no_safepoint_state(self);
228 
229   int wait_status = _lock.wait(timeout);
230   set_owner(self);
231   return wait_status != 0;          // return true IFF timeout
232 }
233 
234 // timeout is in milliseconds - with zero meaning never timeout
235 bool Monitor::wait(uint64_t timeout) {
236   JavaThread* const self = JavaThread::current();
237   // Safepoint checking logically implies an active JavaThread.
238   assert(self->is_active_Java_thread(), "invariant");
239 
240   assert_owner(self);
241   check_rank(self);
242 
243   // conceptually set the owner to null in anticipation of
244   // abdicating the lock in wait
245   set_owner(nullptr);
246 
247   // Check safepoint state after resetting owner and possible NSV.
248   check_safepoint_state(self);
249 
250   int wait_status;
251   InFlightMutexRelease ifmr(this);
252 
253   {
254     ThreadBlockInVMPreprocess<InFlightMutexRelease> tbivmdc(self, ifmr);
255     OSThreadWaitState osts(self->osthread(), false /* not Object.wait() */);
256 
257     wait_status = _lock.wait(timeout);
258   }
259 
260   if (ifmr.not_released()) {
261     // Not unlocked by ~ThreadBlockInVMPreprocess
262     assert_owner(nullptr);
263     // Conceptually reestablish ownership of the lock.
264     set_owner(self);
265   } else {
266     lock(self);
267   }
268 
269   return wait_status != 0;          // return true IFF timeout
270 }
271 
272 static const int MAX_NUM_MUTEX = 1204;
273 static Mutex* _internal_mutex_arr[MAX_NUM_MUTEX];
274 Mutex** Mutex::_mutex_array = _internal_mutex_arr;
275 int Mutex::_num_mutex = 0;
276 
277 void Mutex::add_mutex(Mutex* var) {
278   assert(Mutex::_num_mutex < MAX_NUM_MUTEX, "increase MAX_NUM_MUTEX");
279   Mutex::_mutex_array[_num_mutex++] = var;
280 }
281 
282 Mutex::~Mutex() {
283   assert_owner(nullptr);
284   os::free(const_cast<char*>(_name));
285 }
286 
287 Mutex::Mutex(Rank rank, const char * name, bool allow_vm_block) : _owner(nullptr) {
288   assert(os::mutex_init_done(), "Too early!");
289   assert(name != nullptr, "Mutex requires a name");
290   _name = os::strdup(name, mtInternal);
291 #ifdef ASSERT
292   _allow_vm_block  = allow_vm_block;
293   _rank            = rank;
294   _skip_rank_check = false;
295 
296   assert(_rank >= static_cast<Rank>(0) && _rank <= safepoint, "Bad lock rank %s: %s", rank_name(), name);
297 
298   // The allow_vm_block also includes allowing other non-Java threads to block or
299   // allowing Java threads to block in native.
300   assert(_rank > nosafepoint || _allow_vm_block,
301          "Locks that don't check for safepoint should always allow the vm to block: %s", name);
302 #endif
303 }
304 
305 bool Mutex::owned_by_self() const {
306   return owner() == Thread::current();
307 }
308 
309 void Mutex::print_on_error(outputStream* st) const {
310   st->print("[" PTR_FORMAT, p2i(this));
311   st->print("] %s", _name);
312   st->print(" - owner thread: " PTR_FORMAT, p2i(owner()));
313 }
314 
315 // ----------------------------------------------------------------------------------
316 // Non-product code
317 //
318 #ifdef ASSERT
319 static Mutex::Rank _ranks[] = { Mutex::event, Mutex::service, Mutex::stackwatermark, Mutex::tty, Mutex::oopstorage,
320                                 Mutex::nosafepoint, Mutex::safepoint };
321 
322 static const char* _rank_names[] = { "event", "service", "stackwatermark", "tty", "oopstorage",
323                                      "nosafepoint", "safepoint" };
324 
325 static const int _num_ranks = 7;
326 
327 static const char* rank_name_internal(Mutex::Rank r) {
328   // Find closest rank and print out the name
329   stringStream st;
330   for (int i = 0; i < _num_ranks; i++) {
331     if (r == _ranks[i]) {
332       return _rank_names[i];
333     } else if (r  > _ranks[i] && (i < _num_ranks-1 && r < _ranks[i+1])) {
334       int delta = static_cast<int>(_ranks[i+1]) - static_cast<int>(r);
335       st.print("%s-%d", _rank_names[i+1], delta);
336       return st.as_string();
337     }
338   }
339   return "fail";
340 }
341 
342 const char* Mutex::rank_name() const {
343   return rank_name_internal(_rank);
344 }
345 
346 
347 void Mutex::assert_no_overlap(Rank orig, Rank adjusted, int adjust) {
348   int i = 0;
349   while (_ranks[i] < orig) i++;
350   // underflow is caught in constructor
351   if (i != 0 && adjusted > event && adjusted <= _ranks[i-1]) {
352     ResourceMark rm;
353     assert(adjusted > _ranks[i-1],
354            "Rank %s-%d overlaps with %s",
355            rank_name_internal(orig), adjust, rank_name_internal(adjusted));
356   }
357 }
358 #endif // ASSERT
359 
360 #ifndef PRODUCT
361 void Mutex::print_on(outputStream* st) const {
362   st->print("Mutex: [" PTR_FORMAT "] %s - owner: " PTR_FORMAT,
363             p2i(this), _name, p2i(owner()));
364   if (_allow_vm_block) {
365     st->print("%s", " allow_vm_block");
366   }
367   DEBUG_ONLY(st->print(" %s", rank_name()));
368   st->cr();
369 }
370 
371 void Mutex::print() const {
372   print_on(::tty);
373 }
374 #endif // PRODUCT
375 
376 #ifdef ASSERT
377 void Mutex::assert_owner(Thread * expected) {
378   const char* msg = "invalid owner";
379   if (expected == nullptr) {
380     msg = "should be un-owned";
381   }
382   else if (expected == Thread::current()) {
383     msg = "should be owned by current thread";
384   }
385   assert(owner() == expected,
386          "%s: owner=" INTPTR_FORMAT ", should be=" INTPTR_FORMAT,
387          msg, p2i(owner()), p2i(expected));
388 }
389 
390 Mutex* Mutex::get_least_ranked_lock(Mutex* locks) {
391   Mutex *res, *tmp;
392   for (res = tmp = locks; tmp != nullptr; tmp = tmp->next()) {
393     if (tmp->rank() < res->rank()) {
394       res = tmp;
395     }
396   }
397   return res;
398 }
399 
400 Mutex* Mutex::get_least_ranked_lock_besides_this(Mutex* locks) {
401   Mutex *res, *tmp;
402   for (res = nullptr, tmp = locks; tmp != nullptr; tmp = tmp->next()) {
403     if (tmp != this && (res == nullptr || tmp->rank() < res->rank())) {
404       res = tmp;
405     }
406   }
407   assert(res != this, "invariant");
408   return res;
409 }
410 
411 // Tests for rank violations that might indicate exposure to deadlock.
412 void Mutex::check_rank(Thread* thread) {
413   Mutex* locks_owned = thread->owned_locks();
414 
415   // We expect the locks already acquired to be in increasing rank order,
416   // modulo locks acquired in try_lock_without_rank_check()
417   for (Mutex* tmp = locks_owned; tmp != nullptr; tmp = tmp->next()) {
418     if (tmp->next() != nullptr) {
419       assert(tmp->rank() < tmp->next()->rank()
420              || tmp->skip_rank_check(), "mutex rank anomaly?");
421     }
422   }
423 
424   if (owned_by_self()) {
425     // wait() case
426     Mutex* least = get_least_ranked_lock_besides_this(locks_owned);
427     // For JavaThreads, we enforce not holding locks of rank nosafepoint or lower while waiting
428     // because the held lock has a NoSafepointVerifier so waiting on a lower ranked lock will not be
429     // able to check for safepoints first with a TBIVM.
430     // For all threads, we enforce not holding the tty lock or below, since this could block progress also.
431     // Also "this" should be the monitor with lowest rank owned by this thread.
432     if (least != nullptr && ((least->rank() <= Mutex::nosafepoint && thread->is_Java_thread()) ||
433                            least->rank() <= Mutex::tty ||
434                            least->rank() <= this->rank())) {
435       ResourceMark rm(thread);
436       assert(false, "Attempting to wait on monitor %s/%s while holding lock %s/%s -- "
437              "possible deadlock. %s", name(), rank_name(), least->name(), least->rank_name(),
438              least->rank() <= this->rank() ?
439               "Should wait on the least ranked monitor from all owned locks." :
440              thread->is_Java_thread() ?
441               "Should not block(wait) while holding a lock of rank nosafepoint or below." :
442               "Should not block(wait) while holding a lock of rank tty or below.");
443     }
444   } else {
445     // lock()/lock_without_safepoint_check()/try_lock() case
446     Mutex* least = get_least_ranked_lock(locks_owned);
447     // Deadlock prevention rules require us to acquire Mutexes only in
448     // a global total order. For example, if m1 is the lowest ranked mutex
449     // that the thread holds and m2 is the mutex the thread is trying
450     // to acquire, then deadlock prevention rules require that the rank
451     // of m2 be less than the rank of m1. This prevents circular waits.
452     if (least != nullptr && least->rank() <= this->rank()) {
453       ResourceMark rm(thread);
454       if (least->rank() > Mutex::tty) {
455         // Printing owned locks acquires tty lock. If the least rank was below or equal
456         // tty, then deadlock detection code would circle back here, until we run
457         // out of stack and crash hard. Print locks only when it is safe.
458         thread->print_owned_locks();
459       }
460       assert(false, "Attempting to acquire lock %s/%s out of order with lock %s/%s -- "
461              "possible deadlock", this->name(), this->rank_name(), least->name(), least->rank_name());
462     }
463   }
464 }
465 
466 // Called immediately after lock acquisition or release as a diagnostic
467 // to track the lock-set of the thread.
468 // Rather like an EventListener for _owner (:>).
469 
470 void Mutex::set_owner_implementation(Thread *new_owner) {
471   // This function is solely responsible for maintaining
472   // and checking the invariant that threads and locks
473   // are in a 1/N relation, with some some locks unowned.
474   // It uses the Mutex::_owner, Mutex::_next, and
475   // Thread::_owned_locks fields, and no other function
476   // changes those fields.
477   // It is illegal to set the mutex from one non-null
478   // owner to another--it must be owned by null as an
479   // intermediate state.
480 
481   if (new_owner != nullptr) {
482     // the thread is acquiring this lock
483 
484     assert(new_owner == Thread::current(), "Should I be doing this?");
485     assert(owner() == nullptr, "setting the owner thread of an already owned mutex");
486     raw_set_owner(new_owner); // set the owner
487 
488     // link "this" into the owned locks list
489     this->_next = new_owner->_owned_locks;
490     new_owner->_owned_locks = this;
491 
492     // NSV implied with locking allow_vm_block flag.
493     // The tty_lock is special because it is released for the safepoint by
494     // the safepoint mechanism.
495     if (new_owner->is_Java_thread() && _allow_vm_block && this != tty_lock) {
496       JavaThread::cast(new_owner)->inc_no_safepoint_count();
497     }
498 
499   } else {
500     // the thread is releasing this lock
501 
502     Thread* old_owner = owner();
503     _last_owner = old_owner;
504     _skip_rank_check = false;
505 
506     assert(old_owner != nullptr, "removing the owner thread of an unowned mutex");
507     assert(old_owner == Thread::current(), "removing the owner thread of an unowned mutex");
508 
509     raw_set_owner(nullptr); // set the owner
510 
511     Mutex* locks = old_owner->owned_locks();
512 
513     // remove "this" from the owned locks list
514 
515     Mutex* prev = nullptr;
516     bool found = false;
517     for (; locks != nullptr; prev = locks, locks = locks->next()) {
518       if (locks == this) {
519         found = true;
520         break;
521       }
522     }
523     assert(found, "Removing a lock not owned");
524     if (prev == nullptr) {
525       old_owner->_owned_locks = _next;
526     } else {
527       prev->_next = _next;
528     }
529     _next = nullptr;
530 
531     // ~NSV implied with locking allow_vm_block flag.
532     if (old_owner->is_Java_thread() && _allow_vm_block && this != tty_lock) {
533       JavaThread::cast(old_owner)->dec_no_safepoint_count();
534     }
535   }
536 }
537 #endif // ASSERT
538 
539 // Print all mutexes/monitors that are currently owned by a thread; called
540 // by fatal error handler.
541 void Mutex::print_owned_locks_on_error(outputStream* st) {
542   st->print("VM Mutex/Monitor currently owned by a thread: ");
543   bool none = true;
544   for (int i = 0; i < _num_mutex; i++) {
545     // see if it has an owner
546     if (_mutex_array[i]->owner() != nullptr) {
547       if (none) {
548         // print format used by Mutex::print_on_error()
549         st->print_cr(" ([mutex/lock_event])");
550         none = false;
551       }
552       _mutex_array[i]->print_on_error(st);
553       st->cr();
554     }
555   }
556   if (none) st->print_cr("None");
557 }
558 
559 void Mutex::print_lock_ranks(outputStream* st) {
560   st->print_cr("VM Mutex/Monitor ranks: ");
561 
562 #ifdef ASSERT
563   // Be extra defensive and figure out the bounds on
564   // ranks right here. This also saves a bit of time
565   // in the #ranks*#mutexes loop below.
566   int min_rank = INT_MAX;
567   int max_rank = INT_MIN;
568   for (int i = 0; i < _num_mutex; i++) {
569     Mutex* m = _mutex_array[i];
570     int r = (int) m->rank();
571     if (min_rank > r) min_rank = r;
572     if (max_rank < r) max_rank = r;
573   }
574 
575   // Print the listings rank by rank
576   for (int r = min_rank; r <= max_rank; r++) {
577     bool first = true;
578     for (int i = 0; i < _num_mutex; i++) {
579       Mutex* m = _mutex_array[i];
580       if (r != (int) m->rank()) continue;
581 
582       if (first) {
583         st->cr();
584         st->print_cr("Rank \"%s\":", m->rank_name());
585         first = false;
586       }
587       st->print_cr("  %s", m->name());
588     }
589   }
590 #else
591   st->print_cr("  Only known in debug builds.");
592 #endif // ASSERT
593 }
594 
595 RecursiveMutex::RecursiveMutex() : _sem(1), _owner(nullptr), _recursions(0) {}
596 
597 void RecursiveMutex::lock(Thread* current) {
598   assert(current == Thread::current(), "must be current thread");
599   if (current == _owner) {
600     _recursions++;
601   } else {
602     // can be called by jvmti by VMThread.
603     if (current->is_Java_thread()) {
604       _sem.wait_with_safepoint_check(JavaThread::cast(current));
605     } else {
606       _sem.wait();
607     }
608     _recursions++;
609     assert(_recursions == 1, "should be");
610     _owner = current;
611   }
612 }
613 
614 void RecursiveMutex::unlock(Thread* current) {
615   assert(current == Thread::current(), "must be current thread");
616   assert(current == _owner, "must be owner");
617   _recursions--;
618   if (_recursions == 0) {
619     _owner = nullptr;
620     _sem.signal();
621   }
622 }