1 files changed, 19 insertions, 3 deletions

diff --git a/lib/idr.c b/lib/idr.c
index e728c7fccc4d..1c4f9281f412 100644
--- a/lib/idr.c
+++ b/lib/idr.c
@@ -185,6 +185,7 @@ static int sub_alloc(struct idr *idp, int *starting_id, struct idr_layer **pa)
                         new = get_from_free_list(idp);
                         if (!new)
                                 return -1;
+                        new->layer = l-1;
                         rcu_assign_pointer(p->ary[m], new);
                         p->count++;
                 }
@@ -210,6 +211,7 @@ build_up:
         if (unlikely(!p)) {
                 if (!(p = get_from_free_list(idp)))
                         return -1;
+                p->layer = 0;
                 layers = 1;
         }
         /*
@@ -218,8 +220,14 @@ build_up:
          */
         while ((layers < (MAX_LEVEL - 1)) && (id >= (1 << (layers*IDR_BITS)))) {
                 layers++;
-                if (!p->count)
+                if (!p->count) {
+                        /* special case: if the tree is currently empty,
+                         * then we grow the tree by moving the top node
+                         * upwards.
+                         */
+                        p->layer++;
                         continue;
+                }
                 if (!(new = get_from_free_list(idp))) {
                         /*
                          * The allocation failed.  If we built part of
@@ -237,6 +245,7 @@ build_up:
                 }
                 new->ary[0] = p;
                 new->count = 1;
+                new->layer = layers-1;
                 if (p->bitmap == IDR_FULL)
                         __set_bit(0, &new->bitmap);
                 p = new;
@@ -493,17 +502,21 @@ void *idr_find(struct idr *idp, int id)
         int n;
         struct idr_layer *p;
 
-        n = idp->layers * IDR_BITS;
         p = rcu_dereference(idp->top);
+        if (!p)
+                return NULL;
+        n = (p->layer+1) * IDR_BITS;
 
         /* Mask off upper bits we don't use for the search. */
         id &= MAX_ID_MASK;
 
         if (id >= (1 << n))
                 return NULL;
+        BUG_ON(n == 0);
 
         while (n > 0 && p) {
                 n -= IDR_BITS;
+                BUG_ON(n != p->layer*IDR_BITS);
                 p = rcu_dereference(p->ary[(id >> n) & IDR_MASK]);
         }
         return((void *)p);
@@ -582,8 +595,11 @@ void *idr_replace(struct idr *idp, void *ptr, int id)
         int n;
         struct idr_layer *p, *old_p;
 
-        n = idp->layers * IDR_BITS;
         p = idp->top;
+        if (!p)
+                return ERR_PTR(-EINVAL);
+
+        n = (p->layer+1) * IDR_BITS;
 
         id &= MAX_ID_MASK;