[release/8.0-staging] Fix missing release semantics in VolatilePtr#124118
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[release/8.0-staging] Fix missing release semantics in VolatilePtr#124118github-actions[bot] wants to merge 1 commit intorelease/8.0-stagingfrom
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VolatilePtr inherits from Volatile<P>, which defines operator=(P val) to call VolatileStore() with release semantics (stlr on ARM64). However, VolatilePtr did not declare its own operator=, so the compiler-generated copy/move assignment operator hid the base class operator= and performed plain stores (str) instead, bypassing the memory barrier entirely. This affected all VolatilePtr assignments including DeadlockAwareLock's m_pHoldingThread and Thread's m_pBlockingLock fields, which were being written without release semantics despite being read with acquire semantics (ldapr) on the other side. Fix by adding a using declaration to bring Volatile<P>::operator= into scope, and an explicit copy assignment operator (which the using declaration cannot suppress the compiler from generating).
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Related issue: #124071
Main PR: 124096
Risk: Low, purely adds a barrier which is the intended semantics of the class.
Testing: manual disassembly inspection verified that affected callsite now have appropriate barriers.
Impact: Detected as a non-deterministic lock free race that resulted in crashes in the Roslyn language server for internal customers. Mostly happens with really complex solutions that have a lot of threads accessing GC Statics.
VolatilePtrinherits fromVolatile<P>, which definesoperator=to callVolatileStore()with platform scpecific release semantics. However,VolatilePtrdid not declare its ownoperator=, so the compiler-generated copy/move assignment operator hid the base classoperator=and performed plain stores instead, bypassing memory barriers entirely.Fix by adding a using declaration to bring
Volatile<P>::operator=into scope, and an explicit copy assignment operator (which the using declaration cannot suppress the compiler from generating).