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Subject[RFC PATCH v2 1/1] of: introduce event tracepoints for dynamic device_node lifecyle
Date
From: Tyrel Datwyler <tyreld@linux.vnet.ibm.com>

This patch introduces event tracepoints for tracking a device_nodes
reference cycle as well as reconfig notifications generated in response
to node/property manipulations.

With the recent upstreaming of the refcount API several device_node
underflows and leaks have come to my attention in the pseries (DLPAR)
dynamic logical partitioning code (ie. POWER speak for hotplugging
virtual and physcial resources at runtime such as cpus or IOAs). These
tracepoints provide a easy and quick mechanism for validating the
reference counting of device_nodes during their lifetime.

Further, when pseries lpars are migrated to a different machine we
perform a live update of our device tree to bring it into alignment with
the configuration of the new machine. The of_reconfig_notify trace point
provides a mechanism that can be turned for debuging the device tree
modifications with out having to build a custom kernel to get at the
DEBUG code introduced by commit 00aa37206e1a54 ("of/reconfig: Add debug
output for OF_RECONFIG notifiers").

The following trace events are provided: of_node_get, of_node_put,
of_node_release, and of_reconfig_notify. These trace points require a
kernel built with ftrace support to be enabled. In a typical environment
where debugfs is mounted at /sys/kernel/debug the entire set of
tracepoints can be set with the following:

echo "of:*" > /sys/kernel/debug/tracing/set_event

or

echo 1 > /sys/kernel/debug/tracing/events/of/enable

The following shows the trace point data from a DLPAR remove of a cpu
from a pseries lpar:

cat /sys/kernel/debug/tracing/trace | grep "POWER8@10"

cpuhp/23-147 [023] .... 128.324827:
of_node_put: refcount=5, dn->full_name=/cpus/PowerPC,POWER8@10
cpuhp/23-147 [023] .... 128.324829:
of_node_put: refcount=4, dn->full_name=/cpus/PowerPC,POWER8@10
cpuhp/23-147 [023] .... 128.324829:
of_node_put: refcount=3, dn->full_name=/cpus/PowerPC,POWER8@10
cpuhp/23-147 [023] .... 128.324831:
of_node_put: refcount=2, dn->full_name=/cpus/PowerPC,POWER8@10
drmgr-7284 [009] .... 128.439000:
of_node_put: refcount=1, dn->full_name=/cpus/PowerPC,POWER8@10
drmgr-7284 [009] .... 128.439002:
of_reconfig_notify: action=DETACH_NODE, dn->full_name=/cpus/PowerPC,POWER8@10,
prop->name=null, old_prop->name=null
drmgr-7284 [009] .... 128.439015:
of_node_put: refcount=0, dn->full_name=/cpus/PowerPC,POWER8@10
drmgr-7284 [009] .... 128.439016:
of_node_release: dn->full_name=/cpus/PowerPC,POWER8@10, dn->_flags=4

Signed-off-by: Tyrel Datwyler <tyreld@linux.vnet.ibm.com>
[wsa: fixed commit abbrev and one of the sysfs paths in commit desc,
removed trailing space and fixed pointer declaration in code]
Signed-off-by: Wolfram Sang <wsa+renesas@sang-engineering.com>
---
drivers/of/dynamic.c | 32 ++++++----------
include/trace/events/of.h | 93 +++++++++++++++++++++++++++++++++++++++++++++++
2 files changed, 105 insertions(+), 20 deletions(-)
create mode 100644 include/trace/events/of.h

diff --git a/drivers/of/dynamic.c b/drivers/of/dynamic.c
index ab988d88704da0..b0d6ab5a35b8c6 100644
--- a/drivers/of/dynamic.c
+++ b/drivers/of/dynamic.c
@@ -21,6 +21,9 @@ static struct device_node *kobj_to_device_node(struct kobject *kobj)
return container_of(kobj, struct device_node, kobj);
}

+#define CREATE_TRACE_POINTS
+#include <trace/events/of.h>
+
/**
* of_node_get() - Increment refcount of a node
* @node: Node to inc refcount, NULL is supported to simplify writing of
@@ -30,8 +33,10 @@ static struct device_node *kobj_to_device_node(struct kobject *kobj)
*/
struct device_node *of_node_get(struct device_node *node)
{
- if (node)
+ if (node) {
kobject_get(&node->kobj);
+ trace_of_node_get(refcount_read(&node->kobj.kref.refcount), node->full_name);
+ }
return node;
}
EXPORT_SYMBOL(of_node_get);
@@ -43,8 +48,10 @@ EXPORT_SYMBOL(of_node_get);
*/
void of_node_put(struct device_node *node)
{
- if (node)
+ if (node) {
+ trace_of_node_put(refcount_read(&node->kobj.kref.refcount) - 1, node->full_name);
kobject_put(&node->kobj);
+ }
}
EXPORT_SYMBOL(of_node_put);

@@ -75,24 +82,7 @@ const char *action_names[] = {
int of_reconfig_notify(unsigned long action, struct of_reconfig_data *p)
{
int rc;
-#ifdef DEBUG
- struct of_reconfig_data *pr = p;
-
- switch (action) {
- case OF_RECONFIG_ATTACH_NODE:
- case OF_RECONFIG_DETACH_NODE:
- pr_debug("notify %-15s %pOF\n", action_names[action],
- pr->dn);
- break;
- case OF_RECONFIG_ADD_PROPERTY:
- case OF_RECONFIG_REMOVE_PROPERTY:
- case OF_RECONFIG_UPDATE_PROPERTY:
- pr_debug("notify %-15s %pOF:%s\n", action_names[action],
- pr->dn, pr->prop->name);
- break;
-
- }
-#endif
+ trace_of_reconfig_notify(action, p);
rc = blocking_notifier_call_chain(&of_reconfig_chain, action, p);
return notifier_to_errno(rc);
}
@@ -320,6 +310,8 @@ void of_node_release(struct kobject *kobj)
{
struct device_node *node = kobj_to_device_node(kobj);

+ trace_of_node_release(node);
+
/* We should never be releasing nodes that haven't been detached. */
if (!of_node_check_flag(node, OF_DETACHED)) {
pr_err("ERROR: Bad of_node_put() on %pOF\n", node);
diff --git a/include/trace/events/of.h b/include/trace/events/of.h
new file mode 100644
index 00000000000000..e8b1302a6f0129
--- /dev/null
+++ b/include/trace/events/of.h
@@ -0,0 +1,93 @@
+#undef TRACE_SYSTEM
+#define TRACE_SYSTEM of
+
+#if !defined(_TRACE_OF_H) || defined(TRACE_HEADER_MULTI_READ)
+#define _TRACE_OF_H
+
+#include <linux/of.h>
+#include <linux/tracepoint.h>
+
+DECLARE_EVENT_CLASS(of_node_ref_template,
+
+ TP_PROTO(int refcount, const char *dn_name),
+
+ TP_ARGS(refcount, dn_name),
+
+ TP_STRUCT__entry(
+ __string(dn_name, dn_name)
+ __field(int, refcount)
+ ),
+
+ TP_fast_assign(
+ __assign_str(dn_name, dn_name);
+ __entry->refcount = refcount;
+ ),
+
+ TP_printk("refcount=%d, dn->full_name=%s",
+ __entry->refcount, __get_str(dn_name))
+);
+
+DEFINE_EVENT(of_node_ref_template, of_node_get,
+ TP_PROTO(int refcount, const char *dn_name),
+ TP_ARGS(refcount, dn_name));
+
+DEFINE_EVENT(of_node_ref_template, of_node_put,
+ TP_PROTO(int refcount, const char *dn_name),
+ TP_ARGS(refcount, dn_name));
+
+TRACE_EVENT(of_node_release,
+
+ TP_PROTO(struct device_node *dn),
+
+ TP_ARGS(dn),
+
+ TP_STRUCT__entry(
+ __string(dn_name, dn->full_name)
+ __field(unsigned long, flags)
+ ),
+
+ TP_fast_assign(
+ __assign_str(dn_name, dn->full_name);
+ __entry->flags = dn->_flags;
+ ),
+
+ TP_printk("dn->full_name=%s, dn->_flags=%lu",
+ __get_str(dn_name), __entry->flags)
+);
+
+#define of_reconfig_action_names \
+ {OF_RECONFIG_ATTACH_NODE, "ATTACH_NODE"}, \
+ {OF_RECONFIG_DETACH_NODE, "DETACH_NODE"}, \
+ {OF_RECONFIG_ADD_PROPERTY, "ADD_PROPERTY"}, \
+ {OF_RECONFIG_REMOVE_PROPERTY, "REMOVE_PROPERTY"}, \
+ {OF_RECONFIG_UPDATE_PROPERTY, "UPDATE_PROPERTY"}
+
+TRACE_EVENT(of_reconfig_notify,
+
+ TP_PROTO(unsigned long action, struct of_reconfig_data *ord),
+
+ TP_ARGS(action, ord),
+
+ TP_STRUCT__entry(
+ __field(unsigned long, action)
+ __string(dn_name, ord->dn->full_name)
+ __string(prop_name, ord->prop ? ord->prop->name : "null")
+ __string(oldprop_name, ord->old_prop ? ord->old_prop->name : "null")
+ ),
+
+ TP_fast_assign(
+ __entry->action = action;
+ __assign_str(dn_name, ord->dn->full_name);
+ __assign_str(prop_name, ord->prop ? ord->prop->name : "null");
+ __assign_str(oldprop_name, ord->old_prop ? ord->old_prop->name : "null");
+ ),
+
+ TP_printk("action=%s, dn->full_name=%s, prop->name=%s, old_prop->name=%s",
+ __print_symbolic(__entry->action, of_reconfig_action_names),
+ __get_str(dn_name), __get_str(prop_name), __get_str(oldprop_name))
+);
+
+#endif /* _TRACE_OF_H */
+
+/* This part must be outside protection */
+#include <trace/define_trace.h>
--
2.11.0
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