| 1 | //===-- mutex.h -------------------------------------------------*- C++ -*-===// |
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| 2 | // |
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| 3 | // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions. |
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| 4 | // See https://llvm.org/LICENSE.txt for license information. |
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| 5 | // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception |
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| 6 | // |
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| 7 | //===----------------------------------------------------------------------===// |
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| 8 | |
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| 9 | #ifndef SCUDO_MUTEX_H_ |
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| 10 | #define SCUDO_MUTEX_H_ |
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| 11 | |
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| 12 | #include "atomic_helpers.h" |
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| 13 | #include "common.h" |
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| 14 | #include "thread_annotations.h" |
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| 15 | |
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| 16 | #include <string.h> |
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| 17 | |
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| 18 | #if SCUDO_FUCHSIA |
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| 19 | #include <lib/sync/mutex.h> // for sync_mutex_t |
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| 20 | #endif |
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| 21 | |
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| 22 | namespace scudo { |
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| 23 | |
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| 24 | class CAPABILITY("mutex" ) HybridMutex { |
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| 25 | public: |
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| 26 | bool tryLock() TRY_ACQUIRE(true); |
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| 27 | NOINLINE void lock() ACQUIRE() { |
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| 28 | if (LIKELY(tryLock())) |
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| 29 | return; |
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| 30 | // The compiler may try to fully unroll the loop, ending up in a |
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| 31 | // NumberOfTries*NumberOfYields block of pauses mixed with tryLocks. This |
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| 32 | // is large, ugly and unneeded, a compact loop is better for our purpose |
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| 33 | // here. Use a pragma to tell the compiler not to unroll the loop. |
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| 34 | #ifdef __clang__ |
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| 35 | #pragma nounroll |
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| 36 | #endif |
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| 37 | for (u8 I = 0U; I < NumberOfTries; I++) { |
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| 38 | delayLoop(); |
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| 39 | if (tryLock()) |
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| 40 | return; |
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| 41 | } |
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| 42 | lockSlow(); |
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| 43 | } |
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| 44 | void unlock() RELEASE(); |
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| 45 | |
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| 46 | // TODO(chiahungduan): In general, we may want to assert the owner of lock as |
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| 47 | // well. Given the current uses of HybridMutex, it's acceptable without |
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| 48 | // asserting the owner. Re-evaluate this when we have certain scenarios which |
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| 49 | // requires a more fine-grained lock granularity. |
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| 50 | ALWAYS_INLINE void assertHeld() ASSERT_CAPABILITY(this) { |
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| 51 | if (SCUDO_DEBUG) |
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| 52 | assertHeldImpl(); |
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| 53 | } |
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| 54 | |
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| 55 | private: |
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| 56 | void delayLoop() { |
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| 57 | // The value comes from the average time spent in accessing caches (which |
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| 58 | // are the fastest operations) so that we are unlikely to wait too long for |
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| 59 | // fast operations. |
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| 60 | constexpr u32 SpinTimes = 16; |
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| 61 | volatile u32 V = 0; |
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| 62 | for (u32 I = 0; I < SpinTimes; ++I) { |
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| 63 | u32 Tmp = V + 1; |
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| 64 | V = Tmp; |
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| 65 | } |
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| 66 | } |
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| 67 | |
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| 68 | void assertHeldImpl(); |
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| 69 | |
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| 70 | // TODO(chiahungduan): Adapt this value based on scenarios. E.g., primary and |
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| 71 | // secondary allocator have different allocation times. |
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| 72 | static constexpr u8 NumberOfTries = 32U; |
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| 73 | |
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| 74 | #if SCUDO_LINUX |
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| 75 | atomic_u32 M = {}; |
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| 76 | #elif SCUDO_FUCHSIA |
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| 77 | sync_mutex_t M = {}; |
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| 78 | #endif |
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| 79 | |
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| 80 | void lockSlow() ACQUIRE(); |
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| 81 | }; |
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| 82 | |
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| 83 | class SCOPED_CAPABILITY ScopedLock { |
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| 84 | public: |
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| 85 | explicit ScopedLock(HybridMutex &M) ACQUIRE(M) : Mutex(M) { Mutex.lock(); } |
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| 86 | ~ScopedLock() RELEASE() { Mutex.unlock(); } |
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| 87 | |
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| 88 | private: |
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| 89 | HybridMutex &Mutex; |
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| 90 | |
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| 91 | ScopedLock(const ScopedLock &) = delete; |
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| 92 | void operator=(const ScopedLock &) = delete; |
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| 93 | }; |
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| 94 | |
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| 95 | } // namespace scudo |
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| 96 | |
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| 97 | #endif // SCUDO_MUTEX_H_ |
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| 98 | |
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