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Don't let protected variable access to be reordered after spinlock release.
LWLockAcquireWithVar needs to set the protected variable while holding the spinlock. Need to use a volatile pointer to make sure it doesn't get reordered by the compiler. The other functions that accessed the protected variable already got this right. 9.4 only. Earlier releases didn't have this code, and in master, spinlock release acts as a compiler barrier.
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@ -482,6 +482,7 @@ static inline bool
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LWLockAcquireCommon(LWLock *l, LWLockMode mode, uint64 *valptr, uint64 val)
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{
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volatile LWLock *lock = l;
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volatile uint64 *valp = valptr;
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PGPROC *proc = MyProc;
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bool retry = false;
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bool result = true;
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@ -637,8 +638,8 @@ LWLockAcquireCommon(LWLock *l, LWLockMode mode, uint64 *valptr, uint64 val)
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}
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/* If there's a variable associated with this lock, initialize it */
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if (valptr)
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*valptr = val;
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if (valp)
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*valp = val;
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/* We are done updating shared state of the lock itself. */
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SpinLockRelease(&lock->mutex);
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