On Wed, Feb 04, 2015 at 11:01:00 +0100, Paolo Bonzini wrote:
> On 03/02/2015 23:08, Emilio G. Cota wrote:
> > This matches the semantics of liburcu.
>
> This is not necessary. The two sets of macros are exactly the same, so
> it's okay to use atomic_rcu_read/write.
They're not exactly the same, otherwise the patch would be trivial.
The difference can be seen in the change to the macros' documentation:
On Tue, Feb 03, 2015 at 17:08:18 -0500, Emilio G. Cota wrote:
> This matches the semantics of liburcu.
> --- a/docs/rcu.txt
> +++ b/docs/rcu.txt
(snip)
> - typeof(*p) atomic_rcu_read(p);
> + typeof(p) rcu_dereference(p);
(snip)
> - void atomic_rcu_set(p, typeof(*p) v);
> + void rcu_assign_pointer(p, typeof(p) v);
The liburcu macros take a variable (usually a pointer, hence the
macros' names, but unsigned long is also common), not its address.
These changes require modifications to the calling code as well, e.g.
memory.c:
struct AddressSpace {
...
/* Accessed via RCU. */
struct FlatView *current_map;
...
};
...
struct FlatView *view;
...
- view = atomic_rcu_read(&as->current_map);
+ view = rcu_dereference(as->current_map);
...
- atomic_rcu_set(&as->current_map, new_view);
+ rcu_assign_pointer(as->current_map, new_view);
Thanks,
Emilio
