[POWERPC] Add a warning to help trackdown device_node refcounting bugs

When the refcount for a device node goes to 0, we call the
destructor - of_node_release(). This should only happen if we've
already detached the node from the device tree.

So add a flag OF_DETACHED which tracks detached-ness, and if we
find ourselves in of_node_release() without it set, issue a
warning and don't free the device_node. To avoid warning
continuously reinitialise the kref to a sane value.

Signed-off-by: Michael Ellerman <michael@ellerman.id.au>
Signed-off-by: Paul Mackerras <paulus@samba.org>

1 files changed, 11 insertions, 0 deletions

diff --git a/arch/powerpc/kernel/prom.c b/arch/powerpc/kernel/prom.c
index bcd1c5ed44a3..6d5e601097a0 100644
--- a/arch/powerpc/kernel/prom.c
+++ b/arch/powerpc/kernel/prom.c
@@ -1375,8 +1375,17 @@ static void of_node_release(struct kref *kref)
         struct device_node *node = kref_to_device_node(kref);
         struct property *prop = node->properties;
 
+        /* We should never be releasing nodes that haven't been detached. */
+        if (!of_node_check_flag(node, OF_DETACHED)) {
+                printk("WARNING: Bad of_node_put() on %s\n", node->full_name);
+                dump_stack();
+                kref_init(&node->kref);
+                return;
+        }
+
         if (!of_node_check_flag(node, OF_DYNAMIC))
                 return;
+
         while (prop) {
                 struct property *next = prop->next;
                 kfree(prop->name);
@@ -1457,6 +1466,8 @@ void of_detach_node(const struct device_node *np)
                 prevsib->sibling = np->sibling;
         }
 
+        of_node_set_flag(np, OF_DETACHED);
+
 out_unlock:
         write_unlock(&devtree_lock);
 }