Subject: Re: [PATCH] of: introduce event tracepoints for dynamic device_node lifecyle

From: Frank Rowand <[email-masked]>
Date: Wed, 19 Apr 2017 10:44:17 -0700

On 04/17/17 17:32, Tyrel Datwyler wrote:
> 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 00aa3720.

Is the normal kernel built with CONFIG_DYNAMIC_DEBUG=y?  If so, then
simply removing the "ifdef DEBUG" around the switch in
of_reconfig_notify() would solve that issue.

-Frank

> 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/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 <[email-masked]>
> ---
>  drivers/of/dynamic.c      | 30 ++++++---------
>  include/trace/events/of.h | 93 +++++++++++++++++++++++++++++++++++++++++++++++
>  2 files changed, 105 insertions(+), 18 deletions(-)
>  create mode 100644 include/trace/events/of.h
> 
> diff --git a/drivers/of/dynamic.c b/drivers/of/dynamic.c
> index 888fdbc..85c0966 100644
> --- a/drivers/of/dynamic.c
> +++ b/drivers/of/dynamic.c
> @@ -16,6 +16,9 @@
>  
>  #include "of_private.h"
>  
> +#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
> @@ -25,8 +28,10 @@
>   */
>  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);
> @@ -38,8 +43,10 @@ struct device_node *of_node_get(struct device_node *node)
>   */
>  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);
>  
> @@ -92,24 +99,9 @@ int of_reconfig_notifier_unregister(struct notifier_block *nb)
>  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 %s\n", action_names[action],
> -			pr->dn->full_name);
> -		break;
> -	case OF_RECONFIG_ADD_PROPERTY:
> -	case OF_RECONFIG_REMOVE_PROPERTY:
> -	case OF_RECONFIG_UPDATE_PROPERTY:
> -		pr_debug("notify %-15s %s:%s\n", action_names[action],
> -			pr->dn->full_name, pr->prop->name);
> -		break;
> +	trace_of_reconfig_notify(action, p);
>  
> -	}
> -#endif
>  	rc = blocking_notifier_call_chain(&of_reconfig_chain, action, p);
>  	return notifier_to_errno(rc);
>  }
> @@ -326,6 +318,8 @@ void of_node_release(struct kobject *kobj)
>  	struct device_node *node = kobj_to_device_node(kobj);
>  	struct property *prop = node->properties;
>  
> +	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 %s\n", node->full_name);
> diff --git a/include/trace/events/of.h b/include/trace/events/of.h
> new file mode 100644
> index 0000000..0d53271
> --- /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>
>