1 //===-- tsd_shared.h --------------------------------------------*- C++ -*-===//
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 #ifndef SCUDO_TSD_SHARED_H_
10 #define SCUDO_TSD_SHARED_H_
11 
12 #include "tsd.h"
13 
14 #include "string_utils.h"
15 
16 #if SCUDO_HAS_PLATFORM_TLS_SLOT
17 // This is a platform-provided header that needs to be on the include path when
18 // Scudo is compiled. It must declare a function with the prototype:
19 //   uintptr_t *getPlatformAllocatorTlsSlot()
20 // that returns the address of a thread-local word of storage reserved for
21 // Scudo, that must be zero-initialized in newly created threads.
22 #include "scudo_platform_tls_slot.h"
23 #endif
24 
25 namespace scudo {
26 
27 template <class Allocator, u32 TSDsArraySize, u32 DefaultTSDCount>
28 struct TSDRegistrySharedT {
29   void init(Allocator *Instance) REQUIRES(Mutex) {
30     DCHECK(!Initialized);
31     Instance->init();
32     for (u32 I = 0; I < TSDsArraySize; I++)
33       TSDs[I].init(Instance);
34     const u32 NumberOfCPUs = getNumberOfCPUs();
35     setNumberOfTSDs((NumberOfCPUs == 0) ? DefaultTSDCount
36                                         : Min(NumberOfCPUs, DefaultTSDCount));
37     Initialized = true;
38   }
39 
40   void initOnceMaybe(Allocator *Instance) EXCLUDES(Mutex) {
41     ScopedLock L(Mutex);
42     if (LIKELY(Initialized))
43       return;
44     init(Instance); // Sets Initialized.
45   }
46 
47   void unmapTestOnly(Allocator *Instance) EXCLUDES(Mutex) {
48     for (u32 I = 0; I < TSDsArraySize; I++) {
49       TSDs[I].commitBack(Instance);
50       TSDs[I] = {};
51     }
52     setCurrentTSD(nullptr);
53     ScopedLock L(Mutex);
54     Initialized = false;
55   }
56 
57   void drainCaches(Allocator *Instance) {
58     ScopedLock L(MutexTSDs);
59     for (uptr I = 0; I < NumberOfTSDs; ++I) {
60       TSDs[I].lock();
61       Instance->drainCache(&TSDs[I]);
62       TSDs[I].unlock();
63     }
64   }
65 
66   ALWAYS_INLINE void initThreadMaybe(Allocator *Instance,
67                                      UNUSED bool MinimalInit) {
68     if (LIKELY(getCurrentTSD()))
69       return;
70     initThread(Instance);
71   }
72 
73   // TSDs is an array of locks and which is not supported for marking
74   // thread-safety capability.
75   ALWAYS_INLINE TSD<Allocator> *
76   getTSDAndLock(bool *UnlockRequired) NO_THREAD_SAFETY_ANALYSIS {
77     TSD<Allocator> *TSD = getCurrentTSD();
78     DCHECK(TSD);
79     *UnlockRequired = true;
80     // Try to lock the currently associated context.
81     if (TSD->tryLock())
82       return TSD;
83     // If that fails, go down the slow path.
84     if (TSDsArraySize == 1U) {
85       // Only 1 TSD, not need to go any further.
86       // The compiler will optimize this one way or the other.
87       TSD->lock();
88       return TSD;
89     }
90     return getTSDAndLockSlow(TSD);
91   }
92 
93   void disable() NO_THREAD_SAFETY_ANALYSIS {
94     Mutex.lock();
95     for (u32 I = 0; I < TSDsArraySize; I++)
96       TSDs[I].lock();
97   }
98 
99   void enable() NO_THREAD_SAFETY_ANALYSIS {
100     for (s32 I = static_cast<s32>(TSDsArraySize - 1); I >= 0; I--)
101       TSDs[I].unlock();
102     Mutex.unlock();
103   }
104 
105   bool setOption(Option O, sptr Value) {
106     if (O == Option::MaxTSDsCount)
107       return setNumberOfTSDs(static_cast<u32>(Value));
108     if (O == Option::ThreadDisableMemInit)
109       setDisableMemInit(Value);
110     // Not supported by the TSD Registry, but not an error either.
111     return true;
112   }
113 
114   bool getDisableMemInit() const { return *getTlsPtr() & 1; }
115 
116   void getStats(ScopedString *Str) EXCLUDES(MutexTSDs) {
117     ScopedLock L(MutexTSDs);
118 
119     Str->append("Stats: SharedTSDs: %u available; total %u\n", NumberOfTSDs,
120                 TSDsArraySize);
121     for (uptr I = 0; I < NumberOfTSDs; ++I) {
122       TSDs[I].lock();
123       Str->append("  Shared TSD[%zu]:\n", I);
124       TSDs[I].getCache().getStats(Str);
125       TSDs[I].unlock();
126     }
127   }
128 
129 private:
130   ALWAYS_INLINE uptr *getTlsPtr() const {
131 #if SCUDO_HAS_PLATFORM_TLS_SLOT
132     return reinterpret_cast<uptr *>(getPlatformAllocatorTlsSlot());
133 #else
134     static thread_local uptr ThreadTSD;
135     return &ThreadTSD;
136 #endif
137   }
138 
139   static_assert(alignof(TSD<Allocator>) >= 2, "");
140 
141   ALWAYS_INLINE void setCurrentTSD(TSD<Allocator> *CurrentTSD) {
142     *getTlsPtr() &= 1;
143     *getTlsPtr() |= reinterpret_cast<uptr>(CurrentTSD);
144   }
145 
146   ALWAYS_INLINE TSD<Allocator> *getCurrentTSD() {
147     return reinterpret_cast<TSD<Allocator> *>(*getTlsPtr() & ~1ULL);
148   }
149 
150   bool setNumberOfTSDs(u32 N) EXCLUDES(MutexTSDs) {
151     ScopedLock L(MutexTSDs);
152     if (N < NumberOfTSDs)
153       return false;
154     if (N > TSDsArraySize)
155       N = TSDsArraySize;
156     NumberOfTSDs = N;
157     NumberOfCoPrimes = 0;
158     // Compute all the coprimes of NumberOfTSDs. This will be used to walk the
159     // array of TSDs in a random order. For details, see:
160     // https://lemire.me/blog/2017/09/18/visiting-all-values-in-an-array-exactly-once-in-random-order/
161     for (u32 I = 0; I < N; I++) {
162       u32 A = I + 1;
163       u32 B = N;
164       // Find the GCD between I + 1 and N. If 1, they are coprimes.
165       while (B != 0) {
166         const u32 T = A;
167         A = B;
168         B = T % B;
169       }
170       if (A == 1)
171         CoPrimes[NumberOfCoPrimes++] = I + 1;
172     }
173     return true;
174   }
175 
176   void setDisableMemInit(bool B) {
177     *getTlsPtr() &= ~1ULL;
178     *getTlsPtr() |= B;
179   }
180 
181   NOINLINE void initThread(Allocator *Instance) NO_THREAD_SAFETY_ANALYSIS {
182     initOnceMaybe(Instance);
183     // Initial context assignment is done in a plain round-robin fashion.
184     const u32 Index = atomic_fetch_add(&CurrentIndex, 1U, memory_order_relaxed);
185     setCurrentTSD(&TSDs[Index % NumberOfTSDs]);
186     Instance->callPostInitCallback();
187   }
188 
189   // TSDs is an array of locks which is not supported for marking thread-safety
190   // capability.
191   NOINLINE TSD<Allocator> *getTSDAndLockSlow(TSD<Allocator> *CurrentTSD)
192       EXCLUDES(MutexTSDs) {
193     // Use the Precedence of the current TSD as our random seed. Since we are
194     // in the slow path, it means that tryLock failed, and as a result it's
195     // very likely that said Precedence is non-zero.
196     const u32 R = static_cast<u32>(CurrentTSD->getPrecedence());
197     u32 N, Inc;
198     {
199       ScopedLock L(MutexTSDs);
200       N = NumberOfTSDs;
201       DCHECK_NE(NumberOfCoPrimes, 0U);
202       Inc = CoPrimes[R % NumberOfCoPrimes];
203     }
204     if (N > 1U) {
205       u32 Index = R % N;
206       uptr LowestPrecedence = UINTPTR_MAX;
207       TSD<Allocator> *CandidateTSD = nullptr;
208       // Go randomly through at most 4 contexts and find a candidate.
209       for (u32 I = 0; I < Min(4U, N); I++) {
210         if (TSDs[Index].tryLock()) {
211           setCurrentTSD(&TSDs[Index]);
212           return &TSDs[Index];
213         }
214         const uptr Precedence = TSDs[Index].getPrecedence();
215         // A 0 precedence here means another thread just locked this TSD.
216         if (Precedence && Precedence < LowestPrecedence) {
217           CandidateTSD = &TSDs[Index];
218           LowestPrecedence = Precedence;
219         }
220         Index += Inc;
221         if (Index >= N)
222           Index -= N;
223       }
224       if (CandidateTSD) {
225         CandidateTSD->lock();
226         setCurrentTSD(CandidateTSD);
227         return CandidateTSD;
228       }
229     }
230     // Last resort, stick with the current one.
231     CurrentTSD->lock();
232     return CurrentTSD;
233   }
234 
235   atomic_u32 CurrentIndex = {};
236   u32 NumberOfTSDs GUARDED_BY(MutexTSDs) = 0;
237   u32 NumberOfCoPrimes GUARDED_BY(MutexTSDs) = 0;
238   u32 CoPrimes[TSDsArraySize] GUARDED_BY(MutexTSDs) = {};
239   bool Initialized GUARDED_BY(Mutex) = false;
240   HybridMutex Mutex;
241   HybridMutex MutexTSDs;
242   TSD<Allocator> TSDs[TSDsArraySize];
243 };
244 
245 } // namespace scudo
246 
247 #endif // SCUDO_TSD_SHARED_H_
248