Le mercredi 18 janvier 2012 à 22:05 -0800, Hugh Dickins a écrit :
> 2. Make one small adjustment to idr_get_next(): take the height from
> the top layer (stable under RCU) instead of from the root (unprotected
> by RCU), as idr_find() does.
>
> --- 3.2.0+/lib/idr.c 2012-01-04 15:55:44.000000000 -0800
> +++ linux/lib/idr.c 2012-01-18 21:25:36.947963342 -0800
> @@ -605,11 +605,11 @@ void *idr_get_next(struct idr *idp, int
> int n, max;
>
> /* find first ent */
> - n = idp->layers * IDR_BITS;
> - max = 1 << n;
> p = rcu_dereference_raw(idp->top);
> if (!p)
> return NULL;
> + n = (p->layer + 1) * IDR_BITS;
> + max = 1 << n;
>
> while (id < max) {
> while (n > 0 && p) {
Interesting, but should be a patch on its own.
Maybe other idr users can benefit from your idea as well, if patch is
labeled "idr: allow idr_get_next() from rcu_read_lock" or something...
I suggest introducing idr_get_next_rcu() helper to make the check about
rcu cleaner.
idr_get_next_rcu(...)
{
WARN_ON_ONCE(!rcu_read_lock_held());
return idr_get_next(...);
}
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