lib/idr.c: Fix bug introduced by RCU fix

commit 711a49a07f84f914aac26a52143f6e7526571143 upstream.

The last patch to lib/idr.c caused a bug if idr_get_new_above() was
called on an empty idr.

Usually, nodes stay on the same layer.  New layers are added to the top
of the tree.

The exception is idr_get_new_above() on an empty tree: In this case, the
new root node is first added on layer 0, then moved upwards.  p->layer
was not updated.

As usual: You shall never rely on the source code comments, they will
only mislead you.

Signed-off-by: Manfred Spraul <manfred@colorfullife.com>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>

diff --git a/lib/idr.c b/lib/idr.c
index 7a785a0c2ea0fccead72653a0fd66af5111888ea..1c4f9281f412db349d3a80e0ed51e51f6102027c 100644 (file)
--- a/lib/idr.c
+++ b/lib/idr.c
@@ -220,8 +220,14 @@ static int idr_get_empty_slot(struct idr *idp, int starting_id,
         */
        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