Re: [PATCH] powerpc: powernv: Fix refcount leak bug in opal-powercap

[Christophe JAILLET]

Le 17/06/2022 à 07:42, Liang He a écrit :

At 2022-06-17 13:01:27, "Christophe JAILLET" <christophe.jail...@wanadoo.fr> 
wrote:

Le 17/06/2022 à 06:20, Liang He a écrit :

In opal_powercap_init(), of_find_compatible_node() will return
a node pointer with refcount incremented. We should use of_node_put()
in fail path or when it is not used anymore.

Besides, for_each_child_of_node() will automatically *inc* and *dec*
refcount during iteration. However, we should add the of_node_put()
if there is a break.

Hi,

I'm not sure that your patch is right here. Because of this *inc* and
*dec* things, do we still need to of_node_put(powercap) once we have
entered for_each_child_of_node?

I think that this reference will be released on the first iteration of
the loop.

Hi, CJ,

Thanks for your reply and I want have a discuss.

Based on my review on the src of 'of_get_next_child',  there is only
*inc* for next and *dec* for pre as follow.

(|node| == powercap)
======__of_get_next_child( |node|, prev)======
      ...
         next = prev? prev->sibling:|node|->child;
        of_node_get(next);
        of_node_put(prev);
      ...
=========================

However, there is no any code to release the |node| (i.e., *powercap*).

Am I right?   If I am wrong, please correct me, thanks.

You are right.
I mis-read __of_get_next_child(().

CJ

Maybe of_node_put(powercap) should be duplicated everywhere it is
relevant and removed from the error handling path?
Or an additional reference should be taken before the loop?
Or adding a new label with "powercap = NULL" and branching there when
needed?

CJ

If my understanding is right, I think current patch is right.

Otherwise, I will make a new patch to handle that, Thanks.

Liang

Signed-off-by: Liang He <win...@126.com>
---
   arch/powerpc/platforms/powernv/opal-powercap.c | 5 ++++-
   1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/arch/powerpc/platforms/powernv/opal-powercap.c 
b/arch/powerpc/platforms/powernv/opal-powercap.c
index 64506b46e77b..b102477d3f95 100644
--- a/arch/powerpc/platforms/powernv/opal-powercap.c
+++ b/arch/powerpc/platforms/powernv/opal-powercap.c
@@ -153,7 +153,7 @@ void __init opal_powercap_init(void)
        pcaps = kcalloc(of_get_child_count(powercap), sizeof(*pcaps),
                        GFP_KERNEL);
        if (!pcaps)
-               return;
+               goto out_powercap;

powercap_kobj = kobject_create_and_add("powercap", opal_kobj);

        if (!powercap_kobj) {
@@ -236,6 +236,9 @@ void __init opal_powercap_init(void)
                kfree(pcaps[i].pg.name);
        }
        kobject_put(powercap_kobj);
+       of_node_put(node);
   out_pcaps:
        kfree(pcaps);
+out_powercap:
+       of_node_put(powercap);
   }