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idr: make idr_get_next() good for rcu_read_lock()

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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 <hughd@google.com>
Acked-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Acked-by: Li Zefan <lizf@cn.fujitsu.com>
Cc: Eric Dumazet <eric.dumazet@gmail.com>
Acked-by: Tejun Heo <tj@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
This commit is contained in:
Hugh Dickins
2012-03-21 16:34:20 -07:00
committed by Linus Torvalds
parent 0e79dedde9
commit 9f7de8275b
1 changed files with 5 additions and 3 deletions
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8
lib/idr.c
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@@ -595,8 +595,10 @@ EXPORT_SYMBOL(idr_for_each);
* Returns pointer to registered object with id, which is next number to * 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 * given id. After being looked up, *@nextidp will be updated for the next
* iteration. * 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) void *idr_get_next(struct idr *idp, int *nextidp)
{ {
struct idr_layer *p, *pa[MAX_LEVEL]; struct idr_layer *p, *pa[MAX_LEVEL];
@@ -605,11 +607,11 @@ void *idr_get_next(struct idr *idp, int *nextidp)
int n, max; int n, max;
/* find first ent */ /* find first ent */
n = idp->layers * IDR_BITS;
max = 1 << n;
p = rcu_dereference_raw(idp->top); p = rcu_dereference_raw(idp->top);
if (!p) if (!p)
return NULL; return NULL;
n = (p->layer + 1) * IDR_BITS;
max = 1 << n;
while (id < max) { while (id < max) {
while (n > 0 && p) { while (n > 0 && p) {