libsanitizer/tsan/tsan_mutex.cc

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