1 /*
  2  * Copyright (c) 1998, 2023, 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 "precompiled.hpp"
 26 #include "logging/log.hpp"
 27 #include "memory/resourceArea.hpp"
 28 #include "runtime/interfaceSupport.inline.hpp"
 29 #include "runtime/javaThread.inline.hpp"
 30 #include "runtime/mutex.hpp"
 31 #include "runtime/os.inline.hpp"
 32 #include "runtime/osThread.hpp"
 33 #include "runtime/safepointMechanism.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   if (!_lock.try_lock()) {
123     // The lock is contended, use contended slow-path function to lock
124     lock_contended(self);
125   }
126 
127   assert_owner(nullptr);
128   set_owner(self);
129 }
130 
131 void Mutex::lock() {
132   lock(Thread::current());
133 }
134 
135 // Lock without safepoint check - a degenerate variant of lock() for use by
136 // JavaThreads when it is known to be safe to not check for a safepoint when
137 // acquiring this lock. If the thread blocks acquiring the lock it is not
138 // safepoint-safe and so will prevent a safepoint from being reached. If used
139 // in the wrong way this can lead to a deadlock with the safepoint code.
140 
141 void Mutex::lock_without_safepoint_check(Thread * self) {
142   assert(owner() != self, "invariant");
143 
144   check_no_safepoint_state(self);
145   check_rank(self);
146 
147   _lock.lock();
148   assert_owner(nullptr);
149   set_owner(self);
150 }
151 
152 void Mutex::lock_without_safepoint_check() {
153   lock_without_safepoint_check(Thread::current());
154 }
155 
156 
157 // Returns true if thread succeeds in grabbing the lock, otherwise false.
158 bool Mutex::try_lock_inner(bool do_rank_checks) {
159   Thread * const self = Thread::current();
160   // Checking the owner hides the potential difference in recursive locking behaviour
161   // on some platforms.
162   if (owner() == self) {
163     return false;
164   }
165 
166   if (do_rank_checks) {
167     check_rank(self);
168   }
169   // Some safepoint checking locks use try_lock, so cannot check
170   // safepoint state, but can check blocking state.
171   check_block_state(self);
172 
173   if (_lock.try_lock()) {
174     assert_owner(nullptr);
175     set_owner(self);
176     return true;
177   }
178   return false;
179 }
180 
181 bool Mutex::try_lock() {
182   return try_lock_inner(true /* do_rank_checks */);
183 }
184 
185 bool Mutex::try_lock_without_rank_check() {
186   bool res = try_lock_inner(false /* do_rank_checks */);
187   DEBUG_ONLY(if (res) _skip_rank_check = true;)
188   return res;
189 }
190 
191 void Mutex::release_for_safepoint() {
192   assert_owner(nullptr);
193   _lock.unlock();
194 }
195 
196 void Mutex::unlock() {
197   DEBUG_ONLY(assert_owner(Thread::current()));
198   set_owner(nullptr);
199   _lock.unlock();
200 }
201 
202 void Monitor::notify() {
203   DEBUG_ONLY(assert_owner(Thread::current()));
204   _lock.notify();
205 }
206 
207 void Monitor::notify_all() {
208   DEBUG_ONLY(assert_owner(Thread::current()));
209   _lock.notify_all();
210 }
211 
212 // timeout is in milliseconds - with zero meaning never timeout
213 bool Monitor::wait_without_safepoint_check(uint64_t timeout) {
214   Thread* const self = Thread::current();
215 
216   assert_owner(self);
217   check_rank(self);
218 
219   // conceptually set the owner to null in anticipation of
220   // abdicating the lock in wait
221   set_owner(nullptr);
222 
223   // Check safepoint state after resetting owner and possible NSV.
224   check_no_safepoint_state(self);
225 
226   int wait_status = _lock.wait(timeout);
227   set_owner(self);
228   return wait_status != 0;          // return true IFF timeout
229 }
230 
231 // timeout is in milliseconds - with zero meaning never timeout
232 bool Monitor::wait(uint64_t timeout) {
233   JavaThread* const self = JavaThread::current();
234   // Safepoint checking logically implies an active JavaThread.
235   assert(self->is_active_Java_thread(), "invariant");
236 
237   assert_owner(self);
238   check_rank(self);
239 
240   // conceptually set the owner to null in anticipation of
241   // abdicating the lock in wait
242   set_owner(nullptr);
243 
244   // Check safepoint state after resetting owner and possible NSV.
245   check_safepoint_state(self);
246 
247   int wait_status;
248   InFlightMutexRelease ifmr(this);
249 
250   {
251     ThreadBlockInVMPreprocess<InFlightMutexRelease> tbivmdc(self, ifmr);
252     OSThreadWaitState osts(self->osthread(), false /* not Object.wait() */);
253 
254     wait_status = _lock.wait(timeout);
255   }
256 
257   if (ifmr.not_released()) {
258     // Not unlocked by ~ThreadBlockInVMPreprocess
259     assert_owner(nullptr);
260     // Conceptually reestablish ownership of the lock.
261     set_owner(self);
262   } else {
263     lock(self);
264   }
265 
266   return wait_status != 0;          // return true IFF timeout
267 }
268 
269 Mutex::~Mutex() {
270   assert_owner(nullptr);
271   os::free(const_cast<char*>(_name));
272 }
273 
274 Mutex::Mutex(Rank rank, const char * name, bool allow_vm_block) : _owner(nullptr), _id(-1) {
275   assert(os::mutex_init_done(), "Too early!");
276   assert(name != nullptr, "Mutex requires a name");
277   _name = os::strdup(name, mtInternal);
278   _id = MutexLocker::name2id(name);
279 #ifdef ASSERT
280   _allow_vm_block  = allow_vm_block;
281   _rank            = rank;
282   _skip_rank_check = false;
283 
284   assert(_rank >= static_cast<Rank>(0) && _rank <= safepoint, "Bad lock rank %s: %s", rank_name(), name);
285 
286   // The allow_vm_block also includes allowing other non-Java threads to block or
287   // allowing Java threads to block in native.
288   assert(_rank > nosafepoint || _allow_vm_block,
289          "Locks that don't check for safepoint should always allow the vm to block: %s", name);
290 #endif
291 }
292 
293 bool Mutex::owned_by_self() const {
294   return owner() == Thread::current();
295 }
296 
297 void Mutex::print_on_error(outputStream* st) const {
298   st->print("[" PTR_FORMAT, p2i(this));
299   st->print("] %s", _name);
300   st->print(" - owner thread: " PTR_FORMAT, p2i(owner()));
301 }
302 
303 // ----------------------------------------------------------------------------------
304 // Non-product code
305 //
306 #ifdef ASSERT
307 static Mutex::Rank _ranks[] = { Mutex::event, Mutex::service, Mutex::stackwatermark, Mutex::tty, Mutex::oopstorage,
308                                 Mutex::nosafepoint, Mutex::safepoint };
309 
310 static const char* _rank_names[] = { "event", "service", "stackwatermark", "tty", "oopstorage",
311                                      "nosafepoint", "safepoint" };
312 
313 static const int _num_ranks = 7;
314 
315 static const char* rank_name_internal(Mutex::Rank r) {
316   // Find closest rank and print out the name
317   stringStream st;
318   for (int i = 0; i < _num_ranks; i++) {
319     if (r == _ranks[i]) {
320       return _rank_names[i];
321     } else if (r  > _ranks[i] && (i < _num_ranks-1 && r < _ranks[i+1])) {
322       int delta = static_cast<int>(_ranks[i+1]) - static_cast<int>(r);
323       st.print("%s-%d", _rank_names[i+1], delta);
324       return st.as_string();
325     }
326   }
327   return "fail";
328 }
329 
330 const char* Mutex::rank_name() const {
331   return rank_name_internal(_rank);
332 }
333 
334 
335 void Mutex::assert_no_overlap(Rank orig, Rank adjusted, int adjust) {
336   int i = 0;
337   while (_ranks[i] < orig) i++;
338   // underflow is caught in constructor
339   if (i != 0 && adjusted > event && adjusted <= _ranks[i-1]) {
340     ResourceMark rm;
341     assert(adjusted > _ranks[i-1],
342            "Rank %s-%d overlaps with %s",
343            rank_name_internal(orig), adjust, rank_name_internal(adjusted));
344   }
345 }
346 #endif // ASSERT
347 
348 #ifndef PRODUCT
349 void Mutex::print_on(outputStream* st) const {
350   st->print("Mutex: [" PTR_FORMAT "] %s - owner: " PTR_FORMAT,
351             p2i(this), _name, p2i(owner()));
352   if (_allow_vm_block) {
353     st->print("%s", " allow_vm_block");
354   }
355   DEBUG_ONLY(st->print(" %s", rank_name()));
356   st->cr();
357 }
358 
359 void Mutex::print() const {
360   print_on(::tty);
361 }
362 #endif // PRODUCT
363 
364 #ifdef ASSERT
365 void Mutex::assert_owner(Thread * expected) {
366   const char* msg = "invalid owner";
367   if (expected == nullptr) {
368     msg = "should be un-owned";
369   }
370   else if (expected == Thread::current()) {
371     msg = "should be owned by current thread";
372   }
373   assert(owner() == expected,
374          "%s: owner=" INTPTR_FORMAT ", should be=" INTPTR_FORMAT,
375          msg, p2i(owner()), p2i(expected));
376 }
377 
378 Mutex* Mutex::get_least_ranked_lock(Mutex* locks) {
379   Mutex *res, *tmp;
380   for (res = tmp = locks; tmp != nullptr; tmp = tmp->next()) {
381     if (tmp->rank() < res->rank()) {
382       res = tmp;
383     }
384   }
385   return res;
386 }
387 
388 Mutex* Mutex::get_least_ranked_lock_besides_this(Mutex* locks) {
389   Mutex *res, *tmp;
390   for (res = nullptr, tmp = locks; tmp != nullptr; tmp = tmp->next()) {
391     if (tmp != this && (res == nullptr || tmp->rank() < res->rank())) {
392       res = tmp;
393     }
394   }
395   assert(res != this, "invariant");
396   return res;
397 }
398 
399 // Tests for rank violations that might indicate exposure to deadlock.
400 void Mutex::check_rank(Thread* thread) {
401   Mutex* locks_owned = thread->owned_locks();
402 
403   // We expect the locks already acquired to be in increasing rank order,
404   // modulo locks acquired in try_lock_without_rank_check()
405   for (Mutex* tmp = locks_owned; tmp != nullptr; tmp = tmp->next()) {
406     if (tmp->next() != nullptr) {
407       assert(tmp->rank() < tmp->next()->rank()
408              || tmp->skip_rank_check(), "mutex rank anomaly?");
409     }
410   }
411 
412   if (owned_by_self()) {
413     // wait() case
414     Mutex* least = get_least_ranked_lock_besides_this(locks_owned);
415     // For JavaThreads, we enforce not holding locks of rank nosafepoint or lower while waiting
416     // because the held lock has a NoSafepointVerifier so waiting on a lower ranked lock will not be
417     // able to check for safepoints first with a TBIVM.
418     // For all threads, we enforce not holding the tty lock or below, since this could block progress also.
419     // Also "this" should be the monitor with lowest rank owned by this thread.
420     if (least != nullptr && ((least->rank() <= Mutex::nosafepoint && thread->is_Java_thread()) ||
421                            least->rank() <= Mutex::tty ||
422                            least->rank() <= this->rank())) {
423       ResourceMark rm(thread);
424       assert(false, "Attempting to wait on monitor %s/%s while holding lock %s/%s -- "
425              "possible deadlock. %s", name(), rank_name(), least->name(), least->rank_name(),
426              least->rank() <= this->rank() ?
427               "Should wait on the least ranked monitor from all owned locks." :
428              thread->is_Java_thread() ?
429               "Should not block(wait) while holding a lock of rank nosafepoint or below." :
430               "Should not block(wait) while holding a lock of rank tty or below.");
431     }
432   } else {
433     // lock()/lock_without_safepoint_check()/try_lock() case
434     Mutex* least = get_least_ranked_lock(locks_owned);
435     // Deadlock prevention rules require us to acquire Mutexes only in
436     // a global total order. For example, if m1 is the lowest ranked mutex
437     // that the thread holds and m2 is the mutex the thread is trying
438     // to acquire, then deadlock prevention rules require that the rank
439     // of m2 be less than the rank of m1. This prevents circular waits.
440     if (least != nullptr && least->rank() <= this->rank()) {
441       ResourceMark rm(thread);
442       if (least->rank() > Mutex::tty) {
443         // Printing owned locks acquires tty lock. If the least rank was below or equal
444         // tty, then deadlock detection code would circle back here, until we run
445         // out of stack and crash hard. Print locks only when it is safe.
446         thread->print_owned_locks();
447       }
448       assert(false, "Attempting to acquire lock %s/%s out of order with lock %s/%s -- "
449              "possible deadlock", this->name(), this->rank_name(), least->name(), least->rank_name());
450     }
451   }
452 }
453 
454 // Called immediately after lock acquisition or release as a diagnostic
455 // to track the lock-set of the thread.
456 // Rather like an EventListener for _owner (:>).
457 
458 void Mutex::set_owner_implementation(Thread *new_owner) {
459   // This function is solely responsible for maintaining
460   // and checking the invariant that threads and locks
461   // are in a 1/N relation, with some some locks unowned.
462   // It uses the Mutex::_owner, Mutex::_next, and
463   // Thread::_owned_locks fields, and no other function
464   // changes those fields.
465   // It is illegal to set the mutex from one non-null
466   // owner to another--it must be owned by null as an
467   // intermediate state.
468 
469   if (new_owner != nullptr) {
470     // the thread is acquiring this lock
471 
472     assert(new_owner == Thread::current(), "Should I be doing this?");
473     assert(owner() == nullptr, "setting the owner thread of an already owned mutex");
474     raw_set_owner(new_owner); // set the owner
475 
476     // link "this" into the owned locks list
477     this->_next = new_owner->_owned_locks;
478     new_owner->_owned_locks = this;
479 
480     // NSV implied with locking allow_vm_block flag.
481     // The tty_lock is special because it is released for the safepoint by
482     // the safepoint mechanism.
483     if (new_owner->is_Java_thread() && _allow_vm_block && this != tty_lock) {
484       JavaThread::cast(new_owner)->inc_no_safepoint_count();
485     }
486 
487   } else {
488     // the thread is releasing this lock
489 
490     Thread* old_owner = owner();
491     _last_owner = old_owner;
492     _skip_rank_check = false;
493 
494     assert(old_owner != nullptr, "removing the owner thread of an unowned mutex");
495     assert(old_owner == Thread::current(), "removing the owner thread of an unowned mutex");
496 
497     raw_set_owner(nullptr); // set the owner
498 
499     Mutex* locks = old_owner->owned_locks();
500 
501     // remove "this" from the owned locks list
502 
503     Mutex* prev = nullptr;
504     bool found = false;
505     for (; locks != nullptr; prev = locks, locks = locks->next()) {
506       if (locks == this) {
507         found = true;
508         break;
509       }
510     }
511     assert(found, "Removing a lock not owned");
512     if (prev == nullptr) {
513       old_owner->_owned_locks = _next;
514     } else {
515       prev->_next = _next;
516     }
517     _next = nullptr;
518 
519     // ~NSV implied with locking allow_vm_block flag.
520     if (old_owner->is_Java_thread() && _allow_vm_block && this != tty_lock) {
521       JavaThread::cast(old_owner)->dec_no_safepoint_count();
522     }
523   }
524 }
525 #endif // ASSERT