On Tue, Feb 12, 2008 at 08:07:29AM -0800, Paul E. McKenney wrote:
...
> "All programmers are blind, especially me."
Hmm... I got it my way: you - superheroes - sometimes seem to be just
like us - common people... (Probably early in the morning, before
dressing your funny costumes?)
> You are right, Jarek. I ran this through gcc, and the following
> comes close:
>
> #define rcu_assign_pointer(p, v) \
> ({ \
> if (!__builtin_constant_p(v) || (v)) \
> smp_wmb(); \
> (p) = (v); \
> })
>
> But I am concerned about the following case:
>
> rcu_assign_pointer(global_index, 0);
>
> . . .
>
> x = global_array[rcu_dereference(global_index)];
>
> Since arrays have a zero-th element, we would really want a memory
> barrier in this case.
It seems the above version of this macro uses the barrier for 0, but
if I miss something, or for these other: documenting reasons, then of
course you are right.
>
> So how about leaving the index-unfriendly version of rcu_assign_pointer()
> and adding an rcu_assign_index() as follows?
>
> Thanx, Paul
>
> Signed-off-by: Paul E. McKenney <[EMAIL PROTECTED]>
> ---
>
> rcupdate.h | 18 ++++++++++++++++++
> 1 file changed, 18 insertions(+)
>
> diff -urpNa -X dontdiff linux-2.6.24/include/linux/rcupdate.h
> linux-2.6.24-rai/include/linux/rcupdate.h
> --- linux-2.6.24/include/linux/rcupdate.h 2008-01-24 14:58:37.000000000
> -0800
> +++ linux-2.6.24-rai/include/linux/rcupdate.h 2008-02-12 08:04:59.000000000
> -0800
> @@ -278,6 +278,24 @@ extern struct lockdep_map rcu_lock_map;
> })
>
> /**
> + * rcu_assign_index - assign (publicize) a index of a newly
> + * initialized array elementg that will be dereferenced by RCU
---------------------------^
+ * initialized array element that will be dereferenced by RCU
Regards,
Jarek P.
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