1//===-- tsan_mutex.cpp ----------------------------------------------------===// 2// 3// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions. 4// See https://llvm.org/LICENSE.txt for license information. 5// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception 6// 7//===----------------------------------------------------------------------===// 8// 9// This file is a part of ThreadSanitizer (TSan), a race detector. 10// 11//===----------------------------------------------------------------------===// 12#include "sanitizer_common/sanitizer_libc.h" 13#include "tsan_mutex.h" 14#include "tsan_platform.h" 15#include "tsan_rtl.h" 16 17namespace __tsan { 18 19// Simple reader-writer spin-mutex. Optimized for not-so-contended case. 20// Readers have preference, can possibly starvate writers. 21 22// The table fixes what mutexes can be locked under what mutexes. 23// E.g. if the row for MutexTypeThreads contains MutexTypeReport, 24// then Report mutex can be locked while under Threads mutex. 25// The leaf mutexes can be locked under any other mutexes. 26// Recursive locking is not supported. 27#if SANITIZER_DEBUG && !SANITIZER_GO 28const MutexType MutexTypeLeaf = (MutexType)-1; 29static MutexType CanLockTab[MutexTypeCount][MutexTypeCount] = { 30 /*0 MutexTypeInvalid*/ {}, 31 /*1 MutexTypeTrace*/ {MutexTypeLeaf}, 32 /*2 MutexTypeThreads*/ {MutexTypeReport}, 33 /*3 MutexTypeReport*/ {MutexTypeSyncVar, 34 MutexTypeMBlock, MutexTypeJavaMBlock}, 35 /*4 MutexTypeSyncVar*/ {MutexTypeDDetector}, 36 /*5 MutexTypeSyncTab*/ {}, // unused 37 /*6 MutexTypeSlab*/ {MutexTypeLeaf}, 38 /*7 MutexTypeAnnotations*/ {}, 39 /*8 MutexTypeAtExit*/ {MutexTypeSyncVar}, 40 /*9 MutexTypeMBlock*/ {MutexTypeSyncVar}, 41 /*10 MutexTypeJavaMBlock*/ {MutexTypeSyncVar}, 42 /*11 MutexTypeDDetector*/ {}, 43 /*12 MutexTypeFired*/ {MutexTypeLeaf}, 44 /*13 MutexTypeRacy*/ {MutexTypeLeaf}, 45 /*14 MutexTypeGlobalProc*/ {}, 46}; 47 48static bool CanLockAdj[MutexTypeCount][MutexTypeCount]; 49#endif 50 51void InitializeMutex() { 52#if SANITIZER_DEBUG && !SANITIZER_GO 53 // Build the "can lock" adjacency matrix. 54 // If [i][j]==true, then one can lock mutex j while under mutex i. 55 const int N = MutexTypeCount; 56 int cnt[N] = {}; 57 bool leaf[N] = {}; 58 for (int i = 1; i < N; i++) { 59 for (int j = 0; j < N; j++) { 60 MutexType z = CanLockTab[i][j]; 61 if (z == MutexTypeInvalid) 62 continue; 63 if (z == MutexTypeLeaf) { 64 CHECK(!leaf[i]); 65 leaf[i] = true; 66 continue; 67 } 68 CHECK(!CanLockAdj[i][(int)z]); 69 CanLockAdj[i][(int)z] = true; 70 cnt[i]++; 71 } 72 } 73 for (int i = 0; i < N; i++) { 74 CHECK(!leaf[i] || cnt[i] == 0); 75 } 76 // Add leaf mutexes. 77 for (int i = 0; i < N; i++) { 78 if (!leaf[i]) 79 continue; 80 for (int j = 0; j < N; j++) { 81 if (i == j || leaf[j] || j == MutexTypeInvalid) 82 continue; 83 CHECK(!CanLockAdj[j][i]); 84 CanLockAdj[j][i] = true; 85 } 86 } 87 // Build the transitive closure. 88 bool CanLockAdj2[MutexTypeCount][MutexTypeCount]; 89 for (int i = 0; i < N; i++) { 90 for (int j = 0; j < N; j++) { 91 CanLockAdj2[i][j] = CanLockAdj[i][j]; 92 } 93 } 94 for (int k = 0; k < N; k++) { 95 for (int i = 0; i < N; i++) { 96 for (int j = 0; j < N; j++) { 97 if (CanLockAdj2[i][k] && CanLockAdj2[k][j]) { 98 CanLockAdj2[i][j] = true; 99 } 100 } 101 } 102 } 103#if 0 104 Printf("Can lock graph:\n"); 105 for (int i = 0; i < N; i++) { 106 for (int j = 0; j < N; j++) { 107 Printf("%d ", CanLockAdj[i][j]); 108 } 109 Printf("\n"); 110 } 111 Printf("Can lock graph closure:\n"); 112 for (int i = 0; i < N; i++) { 113 for (int j = 0; j < N; j++) { 114 Printf("%d ", CanLockAdj2[i][j]); 115 } 116 Printf("\n"); 117 } 118#endif 119 // Verify that the graph is acyclic. 120 for (int i = 0; i < N; i++) { 121 if (CanLockAdj2[i][i]) { 122 Printf("Mutex %d participates in a cycle\n", i); 123 Die(); 124 } 125 } 126#endif 127} 128 129InternalDeadlockDetector::InternalDeadlockDetector() { 130 // Rely on zero initialization because some mutexes can be locked before ctor. 131} 132 133#if SANITIZER_DEBUG && !SANITIZER_GO 134void InternalDeadlockDetector::Lock(MutexType t) { 135 // Printf("LOCK %d @%zu\n", t, seq_ + 1); 136 CHECK_GT(t, MutexTypeInvalid); 137 CHECK_LT(t, MutexTypeCount); 138 u64 max_seq = 0; 139 u64 max_idx = MutexTypeInvalid; 140 for (int i = 0; i != MutexTypeCount; i++) { 141 if (locked_[i] == 0) 142 continue; 143 CHECK_NE(locked_[i], max_seq); 144 if (max_seq < locked_[i]) { 145 max_seq = locked_[i]; 146 max_idx = i; 147 } 148 } 149 locked_[t] = ++seq_; 150 if (max_idx == MutexTypeInvalid) 151 return; 152 // Printf(" last %d @%zu\n", max_idx, max_seq); 153 if (!CanLockAdj[max_idx][t]) { 154 Printf("ThreadSanitizer: internal deadlock detected\n"); 155 Printf("ThreadSanitizer: can't lock %d while under %zu\n", 156 t, (uptr)max_idx); 157 CHECK(0); 158 } 159} 160 161void InternalDeadlockDetector::Unlock(MutexType t) { 162 // Printf("UNLO %d @%zu #%zu\n", t, seq_, locked_[t]); 163 CHECK(locked_[t]); 164 locked_[t] = 0; 165} 166 167void InternalDeadlockDetector::CheckNoLocks() { 168 for (int i = 0; i != MutexTypeCount; i++) { 169 CHECK_EQ(locked_[i], 0); 170 } 171} 172#endif 173 174void CheckNoLocks(ThreadState *thr) { 175#if SANITIZER_DEBUG && !SANITIZER_GO 176 thr->internal_deadlock_detector.CheckNoLocks(); 177#endif 178} 179 180const uptr kUnlocked = 0; 181const uptr kWriteLock = 1; 182const uptr kReadLock = 2; 183 184class Backoff { 185 public: 186 Backoff() 187 : iter_() { 188 } 189 190 bool Do() { 191 if (iter_++ < kActiveSpinIters) 192 proc_yield(kActiveSpinCnt); 193 else 194 internal_sched_yield(); 195 return true; 196 } 197 198 u64 Contention() const { 199 u64 active = iter_ % kActiveSpinIters; 200 u64 passive = iter_ - active; 201 return active + 10 * passive; 202 } 203 204 private: 205 int iter_; 206 static const int kActiveSpinIters = 10; 207 static const int kActiveSpinCnt = 20; 208}; 209 210Mutex::Mutex(MutexType type, StatType stat_type) { 211 CHECK_GT(type, MutexTypeInvalid); 212 CHECK_LT(type, MutexTypeCount); 213#if SANITIZER_DEBUG 214 type_ = type; 215#endif 216#if TSAN_COLLECT_STATS 217 stat_type_ = stat_type; 218#endif 219 atomic_store(&state_, kUnlocked, memory_order_relaxed); 220} 221 222Mutex::~Mutex() { 223 CHECK_EQ(atomic_load(&state_, memory_order_relaxed), kUnlocked); 224} 225 226void Mutex::Lock() { 227#if SANITIZER_DEBUG && !SANITIZER_GO 228 cur_thread()->internal_deadlock_detector.Lock(type_); 229#endif 230 uptr cmp = kUnlocked; 231 if (atomic_compare_exchange_strong(&state_, &cmp, kWriteLock, 232 memory_order_acquire)) 233 return; 234 for (Backoff backoff; backoff.Do();) { 235 if (atomic_load(&state_, memory_order_relaxed) == kUnlocked) { 236 cmp = kUnlocked; 237 if (atomic_compare_exchange_weak(&state_, &cmp, kWriteLock, 238 memory_order_acquire)) { 239#if TSAN_COLLECT_STATS && !SANITIZER_GO 240 StatInc(cur_thread(), stat_type_, backoff.Contention()); 241#endif 242 return; 243 } 244 } 245 } 246} 247 248void Mutex::Unlock() { 249 uptr prev = atomic_fetch_sub(&state_, kWriteLock, memory_order_release); 250 (void)prev; 251 DCHECK_NE(prev & kWriteLock, 0); 252#if SANITIZER_DEBUG && !SANITIZER_GO 253 cur_thread()->internal_deadlock_detector.Unlock(type_); 254#endif 255} 256 257void Mutex::ReadLock() { 258#if SANITIZER_DEBUG && !SANITIZER_GO 259 cur_thread()->internal_deadlock_detector.Lock(type_); 260#endif 261 uptr prev = atomic_fetch_add(&state_, kReadLock, memory_order_acquire); 262 if ((prev & kWriteLock) == 0) 263 return; 264 for (Backoff backoff; backoff.Do();) { 265 prev = atomic_load(&state_, memory_order_acquire); 266 if ((prev & kWriteLock) == 0) { 267#if TSAN_COLLECT_STATS && !SANITIZER_GO 268 StatInc(cur_thread(), stat_type_, backoff.Contention()); 269#endif 270 return; 271 } 272 } 273} 274 275void Mutex::ReadUnlock() { 276 uptr prev = atomic_fetch_sub(&state_, kReadLock, memory_order_release); 277 (void)prev; 278 DCHECK_EQ(prev & kWriteLock, 0); 279 DCHECK_GT(prev & ~kWriteLock, 0); 280#if SANITIZER_DEBUG && !SANITIZER_GO 281 cur_thread()->internal_deadlock_detector.Unlock(type_); 282#endif 283} 284 285void Mutex::CheckLocked() { 286 CHECK_NE(atomic_load(&state_, memory_order_relaxed), 0); 287} 288 289} // namespace __tsan 290