Messages in this thread | | | Subject | Re: [PATCH] memcg: restore ss->id_lock to spinlock, using RCU for next | From | Eric Dumazet <> | Date | Thu, 19 Jan 2012 08:33:21 +0100 |
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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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