Re: [RFC PATCH 1/4] hazptr: Add initial implementation of hazard pointers

[Mathieu Desnoyers]

On 2024-09-25 15:20, Mathieu Desnoyers wrote:
[...]
> static inline
> bool same_ptr(void *a, void *b)
> {
>      asm goto (
>          "cmpq %[a], %[b]\n\t"
>          "jne %l[ne]\n\t"
>          : : [a] "r" (a), [b] "r" (b)
>          : : ne);
>      return true;
> ne:
>      return false;
> }

Based on the information provided in this email thread,
it appears the only concern when it comes to comparing a
pointer loaded by rcu_dereference() with another pointer
is the possibility of compiler optimizations.

In the specific case of hazard pointer hpref_hp_get(), this
function does both loads which are then compared with one
another. Therefore, it is not possible for the user to
provide a comparison value known at compile-time, except
in the unlikely scenario where the hazard pointer would
be const, which does not really make much sense.

Therefore, just using rcu_dereference() for the second
load should be fine.

Thanks,

Mathieu

--
Mathieu Desnoyers
EfficiOS Inc.
https://www.efficios.com