fix(DSM): Use async-signal-safe mutex in SIGSEGV handler#9893
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adambratschikaye wants to merge 2 commits intomasterfrom
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fix(DSM): Use async-signal-safe mutex in SIGSEGV handler#9893adambratschikaye wants to merge 2 commits intomasterfrom
adambratschikaye wants to merge 2 commits intomasterfrom
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std::sync::Mutex uses pthread_mutex_lock internally, which is not async-signal-safe. The SIGSEGV handler acquires two mutexes during execution: the SigsegvMemoryTracker lock and the subtract_instruction_counter lock. If the main thread holds either of these when a page fault fires, the handler will call pthread_mutex_lock re-entrantly on the same thread, which is undefined behaviour and can deadlock the process. Introduce SignalMutex, a thin wrapper around an AtomicBool that uses compare_exchange (Acquire/Relaxed) to take the lock and a Release store to release it. All three operations are async-signal-safe. If the flag is already set when the handler tries to acquire it, SignalMutex panics immediately rather than blocking, turning a silent hang into a loud crash that is easier to diagnose.
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michael-weigelt
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Apr 15, 2026
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std::sync::Mutex uses pthread_mutex_lock internally, which is not async-signal-safe. The SIGSEGV handler acquires two mutexes during execution: the SigsegvMemoryTracker lock and the
subtract_instruction_counter lock. If the main thread holds either of these when a page fault fires, the handler will call pthread_mutex_lock re-entrantly on the same thread, which is undefined behaviour and can deadlock the process.
Introduce SignalMutex, a thin wrapper around an AtomicBool that uses compare_exchange (Acquire/Relaxed) to take the lock and a Release store to release it. All three operations are async-signal-safe. If the flag is already set when the handler tries to acquire it, SignalMutex panics immediately rather than blocking, turning a silent hang into a loud crash that is easier to diagnose.