On Mon, Jan 09, 2006 at 05:32:55PM +0300, Oleg Nesterov wrote:
> Oleg Nesterov wrote:
> >
> > I think it is better to set ->qs_pending = 1 directly in __rcu_pending():
>
> This patch has a bug. I am sending a trivial fix, but now I am not
> sure myself that 1 timer tick saved worth the code uglification.
This is indeed an accident waiting to happen -- someone is bound to
replace the "|" with an "||", a change that is too easy for someone
to miss. Once Vatsa is satisfied with the CPU-hotplug aspects of
this set of patches, if __rcu_pending() still has side-effects, I would
suggest something like the following:
int rcu_pending(int cpu)
{
int retval = 0;
if (__rcu_pending(&rcu_ctrlblk, &per_cpu(rcu_data, cpu)))
retval = 1;
if (__rcu_pending(&rcu_bh_ctrlblk, &per_cpu(rcu_bh_data, cpu)))
retval = 1;
return retval;
}
A few more lines, but the intent is much more clear. And I bet that
gcc generates reasonable code in either case.
Or maybe this is just me...
Thanx, Paul
> [PATCH 6/5] rcu: start new grace period from rcu_pending() fix
>
> We should not miss __rcu_pending(&rcu_bh_ctrlblk) in rcu_pending().
>
> Signed-off-by: Oleg Nesterov <[email protected]>
>
> --- 2.6.15/kernel/rcupdate.c~6_FIX 2006-01-09 00:26:44.000000000 +0300
> +++ 2.6.15/kernel/rcupdate.c 2006-01-09 19:19:27.000000000 +0300
> @@ -464,7 +464,7 @@ static int __rcu_pending(struct rcu_ctrl
>
> int rcu_pending(int cpu)
> {
> - return __rcu_pending(&rcu_ctrlblk, &per_cpu(rcu_data, cpu)) ||
> + return __rcu_pending(&rcu_ctrlblk, &per_cpu(rcu_data, cpu)) |
> __rcu_pending(&rcu_bh_ctrlblk, &per_cpu(rcu_bh_data, cpu));
> }
>
-
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