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

[Rob Herring <robh+dt@kernel.org>]

On Mon, Apr 17, 2017 at 7:32 PM, Tyrel Datwyler
<tyreld@linux.vnet.ibm.com> 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.

Not really relevant for this patch, but since you are looking at
pseries and refcounting, the refcounting largely exists for pseries.
It's also hard to get right as this type of fix is fairly common. It's
now used for overlays, but we really probably only need to refcount
the overlays or changesets as a whole, not at a node level. If you
have any thoughts on how a different model of refcounting could work
for pseries, I'd like to discuss it.

> 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.
>
> 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 <tyreld@linux.vnet.ibm.com>
> ---
>  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);

Seems like there should be a kobj wrapper to read the refcount.

> +       }
>         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>
> --
> 1.8.3.1
>