From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from psmtp.com (na3sys010amx156.postini.com [74.125.245.156]) by kanga.kvack.org (Postfix) with SMTP id 5CCB26B004F for ; Thu, 19 Jan 2012 15:49:02 -0500 (EST) Received: by iadj38 with SMTP id j38so496028iad.14 for ; Thu, 19 Jan 2012 12:49:01 -0800 (PST) Date: Thu, 19 Jan 2012 12:48:48 -0800 (PST) From: Hugh Dickins Subject: [PATCH 1/3] idr: make idr_get_next() good for rcu_read_lock() In-Reply-To: Message-ID: References: <1326958401.1113.22.camel@edumazet-laptop> <1326979818.2249.12.camel@edumazet-HP-Compaq-6005-Pro-SFF-PC> MIME-Version: 1.0 Content-Type: TEXT/PLAIN; charset=US-ASCII Sender: owner-linux-mm@kvack.org List-ID: To: Tejun Heo Cc: Eric Dumazet , Li Zefan , Andrew Morton , Manfred Spraul , KAMEZAWA Hiroyuki , Johannes Weiner , Ying Han , Greg Thelen , cgroups@vger.kernel.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org 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: so that it can be used with RCU locking. Copied comment on RCU locking from idr_find(). Signed-off-by: Hugh Dickins Acked-by: KAMEZAWA Hiroyuki Acked-by: Li Zefan --- lib/idr.c | 8 +++++--- 1 file changed, 5 insertions(+), 3 deletions(-) --- 3.2.0+.orig/lib/idr.c 2012-01-04 15:55:44.000000000 -0800 +++ 3.2.0+/lib/idr.c 2012-01-19 11:55:28.780206713 -0800 @@ -595,8 +595,10 @@ EXPORT_SYMBOL(idr_for_each); * Returns pointer to registered object with id, which is next number to * given id. After being looked up, *@nextidp will be updated for the next * iteration. + * + * This function can be called under rcu_read_lock(), given that the leaf + * pointers lifetimes are correctly managed. */ - void *idr_get_next(struct idr *idp, int *nextidp) { struct idr_layer *p, *pa[MAX_LEVEL]; @@ -605,11 +607,11 @@ 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) { -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Fight unfair telecom internet charges in Canada: sign http://stopthemeter.ca/ Don't email: email@kvack.org