Re: [mainline][DLPAR][Oops] OF: ERROR: Bad of_node_put() on /cpus

From: Michael Ellerman
Date: Wed Sep 20 2017 - 07:39:17 EST

Rob Herring <robh@xxxxxxxxxx> writes:

> On Fri, Sep 15, 2017 at 6:04 AM, abdul <abdhalee@xxxxxxxxxxxxxxxxxx> wrote:
>> Hi,
>> Mainline kernel panics during DLPAR CPU add/remove operation.
>> Machine Type: Power8 PowerVM LPAR
>> kernel 4.13.0
> Did 4.12 work or when was it last working? I'm not seeing anything
> recent in the DT code that looks suspicious.

I'm pretty sure it's:

int dlpar_attach_node(struct device_node *dn, struct device_node *parent)
int rc;

dn->parent = parent;

rc = of_attach_node(dn);
if (rc) {
printk(KERN_ERR "Failed to add device node %pOF\n", dn);
return rc;

HERE ^^^^^^^^^^

return 0;

Prior to 215ee763f8cb ("powerpc: pseries: remove dlpar_attach_node
dependency on full path"), we re-looked up the parent, and got another
reference on it. That meant the put before the return there was correct.
But now it's not because the caller has a reference to parent but it's
not ours to drop.

Testing a fix, will report back.