FAILED: patch "[PATCH] powerpc/sysfs: Fix reference leak of cpu device_nodes present" failed to apply to 4.9-stable tree

FAILED: patch "[PATCH] powerpc/sysfs: Fix reference leak of cpu device_nodes present" failed to apply to 4.9-stable tree

[gregkh]

The patch below does not apply to the 4.9-stable tree.
If someone wants it applied there, or to any other stable or longterm
tree, then please email the backport, including the original git commit
id to <stable@vger.kernel.org>.

thanks,

greg k-h

------------------ original commit in Linus's tree ------------------

>From e76ca27790a514590af782f83f6eae49e0ccf8c9 Mon Sep 17 00:00:00 2001
From: Tyrel Datwyler <tyreld@linux.vnet.ibm.com>
Date: Mon, 17 Apr 2017 20:24:39 -0400
Subject: [PATCH] powerpc/sysfs: Fix reference leak of cpu device_nodes present
 at boot

For CPUs present at boot each logical CPU acquires a reference to the
associated device node of the core. This happens in register_cpu() which
is called by topology_init(). The result of this is that we end up with
a reference held by each thread of the core. However, these references
are never freed if the CPU core is DLPAR removed.

This patch fixes the reference leaks by acquiring and releasing the references
in the CPU hotplug callbacks un/register_cpu_online(). With this patch symmetric
reference counting is observed with both CPUs present at boot, and those DLPAR
added after boot.

Fixes: f86e4718f24b ("driver/core: cpu: initialize of_node in cpu's device struture")
Cc: stable@vger.kernel.org # v3.12+
Signed-off-by: Tyrel Datwyler <tyreld@linux.vnet.ibm.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>

diff --git a/arch/powerpc/kernel/sysfs.c b/arch/powerpc/kernel/sysfs.c
index c1fb255a60d6..949957b97ead 100644
--- a/arch/powerpc/kernel/sysfs.c
+++ b/arch/powerpc/kernel/sysfs.c
@@ -710,6 +710,10 @@ static int register_cpu_online(unsigned int cpu)
 	struct device_attribute *attrs, *pmc_attrs;
 	int i, nattrs;
 
+	/* For cpus present at boot a reference was already grabbed in register_cpu() */
+	if (!s->of_node)
+		s->of_node = of_get_cpu_node(cpu, NULL);
+
 #ifdef CONFIG_PPC64
 	if (cpu_has_feature(CPU_FTR_SMT))
 		device_create_file(s, &dev_attr_smt_snooze_delay);
@@ -864,6 +868,8 @@ static int unregister_cpu_online(unsigned int cpu)
 	}
 #endif
 	cacheinfo_cpu_offline(cpu);
+	of_node_put(s->of_node);
+	s->of_node = NULL;
 #endif /* CONFIG_HOTPLUG_CPU */
 	return 0;
 }