Re: [RFC PATCH v2 1/1] of: introduce event tracepoints for dynamic device_node lifecyle

[Frank Rowand]

On 01/21/18 06:31, Wolfram Sang wrote:
> From: Tyrel Datwyler <tyreld@xxxxxxxxxxxxxxxxxx>
> 
> 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@xxxxxxxxxxxxxxxxxx>
> [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@xxxxxxxxxxxxxxxxxxxx>
> ---
>  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

I overlooked the SPDX identifier.  Please add that to this new file.

-Frank


> @@ -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>
>