[PATCH 1/2] powerpc/pseries: fix of_node_put() underflow during dlpar remove

[Tyrel Datwyler <tyreld@linux.vnet.ibm.com>]

Historically device_node references were tracked using a kref embedded
as a struct field. Commit 75b57ecf9 refactored device_nodes to be
kobjects such that the device tree could by more simply exposed to
userspace using sysfs. Commit 0829f6d1f6 followed up these changes to
better control the kobject lifecycle and in particular the referecne
counting via of_node_get(), of_node_put(), and of_node_init(). A side
effect of this second commit was that it introduced an of_node_put()
call when a dynamic node is detached that removes the initial kobj
reference created by of_node_init() . Traditionally as the original
dynamic device node user the pseries code had assumed responsibilty for
releasing this final reference in its platform specific DLPAR detach code.

This patch fixes a refcount underflow introduced by commit 0829f6d1f6,
and recently exposed by the upstreaming of the recount API.

Messages like the following are no longer seen in the kernel log with this
patch following DLPAR remove operations of cpus and pci devices.

  [  269.589441] rpadlpar_io: slot PHB 72 removed
  [  270.589997] refcount_t: underflow; use-after-free.
  [  270.590019] ------------[ cut here ]------------
  [  270.590025] WARNING: CPU: 5 PID: 3335 at
     lib/refcount.c:128 refcount_sub_and_test+0xf4/0x110

Cc: stable@vger.kernel.org
Fixes: 0829f6d1f69e ("of: device_node kobject lifecycle fixes")
Signed-off-by: Tyrel Datwyler <tyreld@linux.vnet.ibm.com>
---
 arch/powerpc/platforms/pseries/dlpar.c | 1 -
 1 file changed, 1 deletion(-)

diff --git a/arch/powerpc/platforms/pseries/dlpar.c b/arch/powerpc/platforms/pseries/dlpar.c
index 193e052..bda18d8 100644
--- a/arch/powerpc/platforms/pseries/dlpar.c
+++ b/arch/powerpc/platforms/pseries/dlpar.c
@@ -288,7 +288,6 @@ int dlpar_detach_node(struct device_node *dn)
 	if (rc)
 		return rc;
 
-	of_node_put(dn); /* Must decrement the refcount */
 	return 0;
 }
 
-- 
1.8.3.1