C RCU+sync+free
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(*
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* Result: Never
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*
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* This litmus test demonstrates that an RCU reader can never see a write that
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* follows a grace period, if it did not see writes that precede that grace
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* period.
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*
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* This is a typical pattern of RCU usage, where the write before the grace
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* period assigns a pointer, and the writes following the grace period destroy
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* the object that the pointer used to point to.
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*
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* This is one implication of the RCU grace-period guarantee, which says (among
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* other things) that an RCU read-side critical section cannot span a grace period.
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*)
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{
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int x = 1;
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int *y = &x;
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int z = 1;
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}
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P0(int *x, int *z, int **y)
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{
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int *r0;
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int r1;
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rcu_read_lock();
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r0 = rcu_dereference(*y);
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r1 = READ_ONCE(*r0);
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rcu_read_unlock();
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}
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P1(int *x, int *z, int **y)
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{
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rcu_assign_pointer(*y, z);
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synchronize_rcu();
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WRITE_ONCE(*x, 0);
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}
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exists (0:r0=x /\ 0:r1=0)
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