Fix missing release semantics in VolatilePtr#124096
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Fix missing release semantics in VolatilePtr#124096github-actions[bot] wants to merge 1 commit intomainfrom
github-actions[bot] wants to merge 1 commit intomainfrom
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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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I think this is a good fix to get into main for now, while I work on more completely revamping Volatile/VolatilePtr to have fewer dangerous apis that are unexpectedly used. This is also a change suitable for backport for existing customers which have problems. |
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@davidwrighton - can you please approve? |
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Tagging subscribers to this area: @agocke |
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VolatilePtr inherits from
Volatile<P>, which defines operator= 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.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).