idr: make idr_find rcu-safe

Make idr_find rcu-safe: it can now be called inside an rcu_read critical
section.

Signed-off-by: Nadia Derbey <Nadia.Derbey@bull.net>
Reviewed-by: "Paul E. McKenney" <paulmck@us.ibm.com>
Cc: Manfred Spraul <manfred@colorfullife.com>
Cc: Jim Houston <jim.houston@comcast.net>
Cc: Pierre Peiffer <peifferp@gmail.com>
Acked-by: Rik van Riel <riel@redhat.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 6 insertions, 5 deletions

diff --git a/lib/idr.c b/lib/idr.c
index 44ab3b2a4eb..21e12af1f23 100644
--- a/lib/idr.c
+++ b/lib/idr.c
@@ -456,7 +456,8 @@ EXPORT_SYMBOL(idr_destroy);
  * return indicates that @id is not valid or you passed %NULL in
  * idr_get_new().
  *
- * The caller must serialize idr_find() vs idr_get_new() and idr_remove().
+ * This function can be called under rcu_read_lock(), given that the leaf
+ * pointers lifetimes are correctly managed.
  */
 void *idr_find(struct idr *idp, int id)
 {
@@ -464,7 +465,7 @@ void *idr_find(struct idr *idp, int id)
         struct idr_layer *p;
 
         n = idp->layers * IDR_BITS;
-        p = idp->top;
+        p = rcu_dereference(idp->top);
 
         /* Mask off upper bits we don't use for the search. */
         id &= MAX_ID_MASK;
@@ -474,7 +475,7 @@ void *idr_find(struct idr *idp, int id)
 
         while (n > 0 && p) {
                 n -= IDR_BITS;
-                p = p->ary[(id >> n) & IDR_MASK];
+                p = rcu_dereference(p->ary[(id >> n) & IDR_MASK]);
         }
         return((void *)p);
 }
@@ -507,7 +508,7 @@ int idr_for_each(struct idr *idp,
         struct idr_layer **paa = &pa[0];
 
         n = idp->layers * IDR_BITS;
-        p = idp->top;
+        p = rcu_dereference(idp->top);
         max = 1 << n;
 
         id = 0;
@@ -515,7 +516,7 @@ int idr_for_each(struct idr *idp,
                 while (n > 0 && p) {
                         n -= IDR_BITS;
                         *paa++ = p;
-                        p = p->ary[(id >> n) & IDR_MASK];
+                        p = rcu_dereference(p->ary[(id >> n) & IDR_MASK]);
                 }
 
                 if (p) {