From 9f7de8275b46d9d11b1505adbfe6c2bb48df4741 Mon Sep 17 00:00:00 2001 From: Hugh Dickins Date: Wed, 21 Mar 2012 16:34:20 -0700 Subject: [PATCH] idr: make idr_get_next() good for rcu_read_lock() 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 Cc: Eric Dumazet Acked-by: Tejun Heo Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds --- lib/idr.c | 8 +++++--- 1 file changed, 5 insertions(+), 3 deletions(-) diff --git a/lib/idr.c b/lib/idr.c index ed055b297c81..12499ba7967e 100644 --- a/lib/idr.c +++ b/lib/idr.c @@ -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 *nextidp) 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) { -- 2.20.1