Patch "powerpc/pseries: Fix of_node_put() underflow during DLPAR remove" has been added to the 4.11-stable tree

[<gregkh@linuxfoundation.org>]

This is a note to let you know that I've just added the patch titled

    powerpc/pseries: Fix of_node_put() underflow during DLPAR remove

to the 4.11-stable tree which can be found at:
    http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
     powerpc-pseries-fix-of_node_put-underflow-during-dlpar-remove.patch
and it can be found in the queue-4.11 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@vger.kernel.org> know about it.


>From 68baf692c435339e6295cb470ea5545cbc28160e Mon Sep 17 00:00:00 2001
From: Tyrel Datwyler <tyreld@linux.vnet.ibm.com>
Date: Mon, 17 Apr 2017 20:21:40 -0400
Subject: powerpc/pseries: Fix of_node_put() underflow during DLPAR remove

From: Tyrel Datwyler <tyreld@linux.vnet.ibm.com>

commit 68baf692c435339e6295cb470ea5545cbc28160e upstream.

Historically struct device_node references were tracked using a kref embedded as
a struct field. Commit 75b57ecf9d1d ("of: Make device nodes kobjects so they
show up in sysfs") (Mar 2014) refactored device_nodes to be kobjects such that
the device tree could by more simply exposed to userspace using sysfs.

Commit 0829f6d1f69e ("of: device_node kobject lifecycle fixes") (Mar 2014)
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 result of this second commit was that it introduced an of_node_put() call when
a dynamic node is detached, in of_node_remove(), 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.

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

Fixes: 0829f6d1f69e ("of: device_node kobject lifecycle fixes")
Signed-off-by: Tyrel Datwyler <tyreld@linux.vnet.ibm.com>
[mpe: Make change log commit references more verbose]
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

---
 arch/powerpc/platforms/pseries/dlpar.c |    1 -
 1 file changed, 1 deletion(-)

--- 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
 	if (rc)
 		return rc;
 
-	of_node_put(dn); /* Must decrement the refcount */
 	return 0;
 }
 


Patches currently in stable-queue which might be from tyreld@linux.vnet.ibm.com are

queue-4.11/powerpc-sysfs-fix-reference-leak-of-cpu-device_nodes-present-at-boot.patch
queue-4.11/of-fix-cpus-reference-leak-in-of_numa_parse_cpu_nodes.patch
queue-4.11/powerpc-pseries-fix-of_node_put-underflow-during-dlpar-remove.patch