Date:   Sat, 18 Dec 2021 00:32:57 +0800
From:   Jeff Xie <xiehuan09@...il.com>
To:     Masami Hiramatsu <mhiramat@...nel.org>
Cc:     Steven Rostedt <rostedt@...dmis.org>, mingo@...hat.com,
        Tom Zanussi <zanussi@...nel.org>, linux-kernel@...r.kernel.org
Subject: Re: [RFC][PATCH v6 1/5] trace: Add trace any kernel object

Hi Masami,

Thanks for your review.

On Fri, Dec 17, 2021 at 12:51 PM Masami Hiramatsu <mhiramat@...nel.org> wrote:
>
> On Tue, 30 Nov 2021 00:49:47 +0800
> Jeff Xie <xiehuan09@...il.com> wrote:
>
> > Introduce objtrace trigger to get the execution flow by tracing
> > any kernel object in the kernel parameter.
>
> Here, please add simple usage (no need to add output) since we can
> see only this comment after merging this on git log.
> If you run `git log -- kernel/trace/` and search "tracing: Add ",
> then you can see more examples to add a new feature. ;)
>
> What would you think this?
> -----
> Introduce objtrace trigger to get the call flow by tracing
> any kernel object in the function parameter.
>
> The objtrace trigger makes a list of the target object address from
> the given event parameter, and records all kernel function calls
> which has the object address in its parameter.
>
> User can identify the kernel call flow related to the object easily.
>
> Syntax:
> ...
>
> Usage:
> ...

I agree, I will add it.

> -----
>
> >
> > Signed-off-by: Jeff Xie <xiehuan09@...il.com>
> > ---
> >  include/linux/trace_events.h        |   1 +
> >  kernel/trace/Kconfig                |  10 +
> >  kernel/trace/Makefile               |   1 +
> >  kernel/trace/trace.h                |   8 +
> >  kernel/trace/trace_entries.h        |  17 +
> >  kernel/trace/trace_events_trigger.c |   1 +
> >  kernel/trace/trace_object.c         | 534 ++++++++++++++++++++++++++++
> >  kernel/trace/trace_output.c         |  40 +++
> >  8 files changed, 612 insertions(+)
> >  create mode 100644 kernel/trace/trace_object.c
> >
> > diff --git a/include/linux/trace_events.h b/include/linux/trace_events.h
> > index 2d167ac3452c..54baec78ce62 100644
> > --- a/include/linux/trace_events.h
> > +++ b/include/linux/trace_events.h
> > @@ -684,6 +684,7 @@ enum event_trigger_type {
> >       ETT_EVENT_HIST          = (1 << 4),
> >       ETT_HIST_ENABLE         = (1 << 5),
> >       ETT_EVENT_EPROBE        = (1 << 6),
> > +     ETT_TRACE_OBJECT        = (1 << 7),
> >  };
> >
> >  extern int filter_match_preds(struct event_filter *filter, void *rec);
> > diff --git a/kernel/trace/Kconfig b/kernel/trace/Kconfig
> > index 420ff4bc67fd..f69761cbfaaa 100644
> > --- a/kernel/trace/Kconfig
> > +++ b/kernel/trace/Kconfig
> > @@ -237,6 +237,16 @@ config FUNCTION_PROFILER
> >
> >         If in doubt, say N.
> >
> > +config TRACE_OBJECT
> > +     bool "Trace kernel object in function parameter"
> > +     depends on FUNCTION_TRACER
> > +     depends on HAVE_FUNCTION_ARG_ACCESS_API
> > +     select TRACING
> > +     default y
> > +     help
> > +      You can trace the kernel object in the kernel function parameter.
> > +      The kernel object is dynamically specified via event trigger.
> > +
> >  config STACK_TRACER
> >       bool "Trace max stack"
> >       depends on HAVE_FUNCTION_TRACER
> > diff --git a/kernel/trace/Makefile b/kernel/trace/Makefile
> > index bedc5caceec7..b924b8e55922 100644
> > --- a/kernel/trace/Makefile
> > +++ b/kernel/trace/Makefile
> > @@ -67,6 +67,7 @@ obj-$(CONFIG_FUNCTION_GRAPH_TRACER) += trace_functions_graph.o
> >  obj-$(CONFIG_TRACE_BRANCH_PROFILING) += trace_branch.o
> >  obj-$(CONFIG_BLK_DEV_IO_TRACE) += blktrace.o
> >  obj-$(CONFIG_FUNCTION_GRAPH_TRACER) += fgraph.o
> > +obj-$(CONFIG_TRACE_OBJECT) += trace_object.o
> >  ifeq ($(CONFIG_BLOCK),y)
> >  obj-$(CONFIG_EVENT_TRACING) += blktrace.o
> >  endif
> > diff --git a/kernel/trace/trace.h b/kernel/trace/trace.h
> > index 38715aa6cfdf..46a1301ac47a 100644
> > --- a/kernel/trace/trace.h
> > +++ b/kernel/trace/trace.h
> > @@ -54,6 +54,7 @@ enum trace_type {
> >       TRACE_TIMERLAT,
> >       TRACE_RAW_DATA,
> >       TRACE_FUNC_REPEATS,
> > +     TRACE_OBJECT,
> >
> >       __TRACE_LAST_TYPE,
> >  };
> > @@ -469,6 +470,7 @@ extern void __ftrace_bad_type(void);
> >                         TRACE_GRAPH_RET);             \
> >               IF_ASSIGN(var, ent, struct func_repeats_entry,          \
> >                         TRACE_FUNC_REPEATS);                          \
> > +             IF_ASSIGN(var, ent, struct trace_object_entry, TRACE_OBJECT);\
> >               __ftrace_bad_type();                                    \
> >       } while (0)
> >
> > @@ -1531,6 +1533,12 @@ static inline int register_trigger_hist_cmd(void) { return 0; }
> >  static inline int register_trigger_hist_enable_disable_cmds(void) { return 0; }
> >  #endif
> >
> > +#ifdef CONFIG_TRACE_OBJECT
> > +extern int register_trigger_object_cmd(void);
> > +#else
> > +static inline int register_trigger_object_cmd(void) { return 0; }
> > +#endif
> > +
> >  extern int register_trigger_cmds(void);
> >  extern void clear_event_triggers(struct trace_array *tr);
> >
> > diff --git a/kernel/trace/trace_entries.h b/kernel/trace/trace_entries.h
> > index cd41e863b51c..bb120d9498a9 100644
> > --- a/kernel/trace/trace_entries.h
> > +++ b/kernel/trace/trace_entries.h
> > @@ -401,3 +401,20 @@ FTRACE_ENTRY(timerlat, timerlat_entry,
> >                __entry->context,
> >                __entry->timer_latency)
> >  );
> > +
> > +/*
> > + * trace object entry:
> > + */
> > +FTRACE_ENTRY(object, trace_object_entry,
> > +
> > +     TRACE_OBJECT,
> > +
> > +     F_STRUCT(
> > +             __field(        unsigned long,          ip              )
> > +             __field(        unsigned long,          parent_ip       )
> > +             __field(        unsigned long,          object          )
> > +     ),
> > +
> > +     F_printk(" %ps <-- %ps object:%lx\n",
> > +              (void *)__entry->ip, (void *)__entry->parent_ip, __entry->object)
> > +);
> > diff --git a/kernel/trace/trace_events_trigger.c b/kernel/trace/trace_events_trigger.c
> > index 3d5c07239a2a..da2d871fa809 100644
> > --- a/kernel/trace/trace_events_trigger.c
> > +++ b/kernel/trace/trace_events_trigger.c
> > @@ -1687,6 +1687,7 @@ __init int register_trigger_cmds(void)
> >       register_trigger_enable_disable_cmds();
> >       register_trigger_hist_enable_disable_cmds();
> >       register_trigger_hist_cmd();
> > +     register_trigger_object_cmd();
> >
> >       return 0;
> >  }
> > diff --git a/kernel/trace/trace_object.c b/kernel/trace/trace_object.c
> > new file mode 100644
> > index 000000000000..83fccd587b63
> > --- /dev/null
> > +++ b/kernel/trace/trace_object.c
> > @@ -0,0 +1,534 @@
> > +// SPDX-License-Identifier: GPL-2.0
> > +/*
> > + * trace the kernel object in the kernel function parameter
> > + * Copyright (C) 2021 Jeff Xie <xiehuan09@...il.com>
> > + */
> > +
> > +#define pr_fmt(fmt) "trace_object: " fmt
> > +
> > +#include "trace_output.h"
> > +#include <linux/freelist.h>
> > +
> > +static DEFINE_PER_CPU(atomic_t, trace_object_event_disable);
>
> atomic_t is for atomic operation which must be shared among cpus. On the
> other hand, per-cpu variable is used for the core-local storage or flags,
> other cpus never touch it. Thus the per-cpu atomic_t is very strange.
>

>From the patch V1, I cloned it from the  function_test_events_call()
in kernel/trace/trace_events.c

commit: 9ea21c1ecdb35ecdcac5fd9d95f62a1f6a7ffec0
tracing/events: perform function tracing in event selftests
Author:     Steven Rostedt <srostedt@...hat.com>

It should be to prevent being preempted by the interrupt context in
the process of adding one

> > +static DEFINE_RAW_SPINLOCK(object_spin_lock);
> > +static struct trace_event_file event_trace_file;
> > +static const int max_args_num = 6;
> > +static const int max_obj_pool = 10;
> > +static atomic_t trace_object_ref;
> > +static int exit_trace_object(void);
> > +static int init_trace_object(void);
> > +
>
> Please add more comments to the code itself. Explain why this is needed
> and how it works for which case. That will lead deeper understanding.
>

I agree, I will add more comments in the next version.

> > +struct object_instance {
> > +     void *object;
> > +     struct freelist_node free_list;
> > +     struct list_head active_list;
> > +};
> > +
> > +struct obj_pool {
> > +     struct freelist_head free_list;
> > +     struct list_head active_list;
> > +};
> > +static struct obj_pool *obj_pool;
> > +
> > +static bool object_exist(void *obj)
> > +{
> > +     struct object_instance *inst;
> > +     bool ret = false;
> > +
> > +     list_for_each_entry_rcu(inst, &obj_pool->active_list, active_list) {
> > +             if (inst->object == obj) {
> > +                     ret = true;
> > +                     goto out;
> > +             }
> > +     }
> > +out:
> > +     return ret;
> > +}
> > +
> > +static bool object_empty(void)
> > +{
> > +     return list_empty(&obj_pool->active_list);
> > +}
> > +
> > +static void set_trace_object(void *obj)
> > +{
> > +     struct freelist_node *fn;
> > +     struct object_instance *ins;
> > +     unsigned long flags;
> > +
> > +     if (in_nmi())
> > +             return;
> > +
> > +     if (!obj)
> > +             return;
> > +
> > +     if (object_exist(obj))
> > +             return;
> > +
> > +     fn = freelist_try_get(&obj_pool->free_list);
> > +     if (!fn) {
> > +             trace_printk("object_pool is full, can't trace object:0x%px\n", obj);
> > +             return;
> > +     }
> > +
> > +     ins = container_of(fn, struct object_instance, free_list);
> > +     ins->object = obj;
> > +
> > +     raw_spin_lock_irqsave(&object_spin_lock, flags);
> > +     list_add_rcu(&ins->active_list, &obj_pool->active_list);
> > +     raw_spin_unlock_irqrestore(&object_spin_lock, flags);
>
> Please add a comment that why this spinlock is needed here and why
> other operation doesn't need it.

(Only this place has write operations, and it cannot be concurrent)
I agree, I will add it.

> > +}
> > +
> > +static inline void free_free_list_objects(struct freelist_head *head)
> > +{
> > +
> > +     struct object_instance *inst;
> > +     struct freelist_node *node = head->head;
> > +
> > +     while (node) {
> > +             inst = container_of(node, struct object_instance, free_list);
> > +             node = node->next;
> > +             kfree(inst);
>
> Note that this is safe only if this free_list is no more accessed.
>

Maybe it need to use rcu to handle it , I will think about how to  fix
it in the next version.

> > +     }
> > +}
> > +
> > +static inline void free_active_list_objects(struct list_head *head)
> > +{
> > +     struct object_instance *inst;
> > +
> > +     list_for_each_entry_rcu(inst, head, active_list)
> > +             kfree(inst);
>
> No, you can not do this, since the 'inst' is still on the active_list.
> Before freeing the 'inst', you need to do list_del_rcu().
> Moreover, the 'inst' might be still accessed from the callbacks,
> you can not directly free it.
>
> RCU ensures that looping on a list can be done safely before and after
> removing/adding a node, but not ensure it is freeable soon, because
> someone still looking the node.
>
> I guess you may expect that all callbacks are stopped after calling

Yes you guessed it right ;-)

> unregister_ftrace_function(&trace_ops);
>
> but that is wrong. That don't synchronize the callbacks (= wait
> for finishing all running callbacks).
> So, you should use synchronize_rcu() after that.

Thanks,  I will fix it.

> > +}
> > +
> > +static inline void free_object_pool(void)
> > +{
> > +     free_free_list_objects(&obj_pool->free_list);
> > +     free_active_list_objects(&obj_pool->active_list);
>
> BTW, did you also ensure all the trigger callback has been done?
> set_trace_object() has a small time window when the object_instance
> is not linked to both of the free_list and the active_list.
> Thus you have to make sure that the function is never called while
> this function. (How to do it? please write the comment about it)

I ignored this small time window, maybe use the rcu can handle it, I
will think about how to fix it.

> > +     kfree(obj_pool);
> > +}
> > +
> > +
> > +static int init_object_pool(void)
> > +{
> > +     struct object_instance *inst;
> > +     int i, ret = 0;
> > +
> > +     obj_pool = kzalloc(sizeof(*obj_pool), GFP_KERNEL);
> > +     if (!obj_pool) {
> > +             ret = -ENOMEM;
> > +             goto out;
> > +     }
> > +
> > +     INIT_LIST_HEAD(&obj_pool->active_list);
> > +
> > +     for (i = 0; i < max_obj_pool; i++) {
> > +             inst = kzalloc(sizeof(*inst), GFP_KERNEL);
> > +             if (!inst) {
> > +                     free_object_pool();
> > +                     ret = -ENOMEM;
> > +                     goto out;
> > +             }
> > +             freelist_add(&inst->free_list, &obj_pool->free_list);
> > +     }
> > +out:
> > +     return ret;
> > +}
> > +
> > +static void submit_trace_object(unsigned long ip, unsigned long parent_ip,
> > +                              unsigned long object)
> > +{
> > +
> > +     struct trace_buffer *buffer;
> > +     struct ring_buffer_event *event;
> > +     struct trace_object_entry *entry;
> > +     int pc;
> > +
> > +     pc = preempt_count();
> > +     event = trace_event_buffer_lock_reserve(&buffer, &event_trace_file,
> > +                     TRACE_OBJECT, sizeof(*entry), pc);
> > +     if (!event)
> > +             return;
> > +     entry   = ring_buffer_event_data(event);
> > +     entry->ip                       = ip;
> > +     entry->parent_ip                = parent_ip;
> > +     entry->object                   = object;
> > +
> > +     event_trigger_unlock_commit(&event_trace_file, buffer, event,
> > +             entry, pc);
> > +}
> > +
> > +static void
> > +trace_object_events_call(unsigned long ip, unsigned long parent_ip,
> > +             struct ftrace_ops *op, struct ftrace_regs *fregs)
> > +{
> > +     struct pt_regs *pt_regs = ftrace_get_regs(fregs);
> > +     unsigned long obj;
> > +     long disabled;
> > +     int cpu, n;
> > +
> > +     preempt_disable_notrace();
> > +
> > +     cpu = raw_smp_processor_id();
> > +     disabled = atomic_inc_return(&per_cpu(trace_object_event_disable, cpu));
>
> So what is the purpose of this check? (are there any issue if the same
> cpu reenter here?)
>

There may be an interrupt context that can preempt it. I am not yet
sure whether the cpu reenter  will affect it.
I will debug and test it. (Referred from function_test_events_call())

> > +
> > +     if (disabled != 1)
> > +             goto out;
> > +
> > +     if (object_empty())
> > +             goto out;
> > +
> > +     for (n = 0; n < max_args_num; n++) {
> > +             obj = regs_get_kernel_argument(pt_regs, n);
> > +             if (object_exist((void *)obj))
> > +                     submit_trace_object(ip, parent_ip, obj);
>
> Please add a comment why don't you break the loop after finding
> any trace object here.
>
(because the parameters of a function may match multiple objects)
I will add the comment in the next version.

> > +     }
> > +
> > +out:
> > +     atomic_dec(&per_cpu(trace_object_event_disable, cpu));
> > +     preempt_enable_notrace();
> > +}
> > +
> > +static struct ftrace_ops trace_ops = {
> > +     .func  = trace_object_events_call,
> > +     .flags = FTRACE_OPS_FL_SAVE_REGS,
> > +};
> > +
> > +static void
> > +trace_object_trigger(struct event_trigger_data *data,
> > +                struct trace_buffer *buffer,  void *rec,
> > +                struct ring_buffer_event *event)
> > +{
> > +
> > +     struct ftrace_event_field *field = data->private_data;
> > +     void *obj = NULL;
> > +
> > +     memcpy(&obj, rec + field->offset, sizeof(obj));
> > +     set_trace_object(obj);
> > +}
> > +
>
> /* This is clone of event_trigger_free(). */
>
> > +static void
> > +trace_object_trigger_free(struct event_trigger_ops *ops,
> > +                struct event_trigger_data *data)
> > +{
> > +     if (WARN_ON_ONCE(data->ref <= 0))
> > +             return;
> > +
> > +     data->ref--;
> > +     if (!data->ref)
> > +             trigger_data_free(data);
> > +}
> > +
> > +static void
> > +trace_object_count_trigger(struct event_trigger_data *data,
> > +                      struct trace_buffer *buffer, void *rec,
> > +                      struct ring_buffer_event *event)
> > +{
> > +     if (!data->count)
> > +             return;
> > +
> > +     if (data->count != -1)
> > +             (data->count)--;
> > +
> > +     trace_object_trigger(data, buffer, rec, event);
> > +}
> > +
>
> /* This is the clone of event_trigger_init() */
>
> > +static int event_object_trigger_init(struct event_trigger_ops *ops,
> > +                    struct event_trigger_data *data)
> > +{
> > +     data->ref++;
> > +     return 0;
> > +}
>
>
> At this moment, I think cloning those functions are OK. But after merged
> and enough tested, trigger should expose these functions and this
> should use it.

I agree.

>
> BTW, it seems you are sharing the trace object active_list (obj_pool::active_list)
> among all object trace triggers. This means if user sets one objtrace trigger
> on 2 events and remove from one event, the active_list still have the object
> which sets by the event we removed. If it is correct, I think this should be
> noted in the document.
> Something like;
>
> Note that currently this is not designed to trace objects of different types
> at the same time. You must set an objtrace trigger to only one event, or
> you must carefully choose the same type object when you set the objtrace on
> differnt events. Also, the traced object list is not cleared unless all
> triggers are removed.
>
Thanks, I agree, I will add it.
>
> > +
> > +static int
> > +event_trigger_print(const char *name, struct seq_file *m,
> > +                 void *data, char *filter_str)
> > +{
> > +     long count = (long)data;
> > +
> > +     seq_puts(m, name);
> > +
> > +     if (count == -1)
> > +             seq_puts(m, ":unlimited");
> > +     else
> > +             seq_printf(m, ":count=%ld", count);
> > +
> > +     if (filter_str)
> > +             seq_printf(m, " if %s\n", filter_str);
> > +     else
> > +             seq_putc(m, '\n');
> > +
> > +     return 0;
> > +}
> > +
> > +static int
> > +trace_object_trigger_print(struct seq_file *m, struct event_trigger_ops *ops,
> > +                      struct event_trigger_data *data)
> > +{
> > +     return event_trigger_print("objtrace", m, (void *)data->count,
> > +                                data->filter_str);
> > +}
> > +
> > +static struct event_trigger_ops objecttrace_trigger_ops = {
> > +     .func                   = trace_object_trigger,
> > +     .print                  = trace_object_trigger_print,
> > +     .init                   = event_object_trigger_init,
> > +     .free                   = trace_object_trigger_free,
> > +};
> > +
> > +static struct event_trigger_ops objecttrace_count_trigger_ops = {
> > +     .func                   = trace_object_count_trigger,
> > +     .print                  = trace_object_trigger_print,
> > +     .init                   = event_object_trigger_init,
> > +     .free                   = trace_object_trigger_free,
> > +};
> > +
> > +static struct event_trigger_ops *
> > +objecttrace_get_trigger_ops(char *cmd, char *param)
> > +{
> > +     return param ? &objecttrace_count_trigger_ops : &objecttrace_trigger_ops;
> > +}
> > +
> > +static int register_object_trigger(char *glob, struct event_trigger_ops *ops,
> > +                         struct event_trigger_data *data,
> > +                         struct trace_event_file *file)
> > +{
> > +     struct event_trigger_data *test;
> > +     int ret = 0;
> > +
> > +     lockdep_assert_held(&event_mutex);
> > +
> > +     list_for_each_entry(test, &file->triggers, list) {
> > +             if (test->cmd_ops->trigger_type == data->cmd_ops->trigger_type) {
> > +                     ret = -EEXIST;
> > +                     goto out;
> > +             }
> > +     }
> > +
> > +     if (data->ops->init) {
> > +             ret = data->ops->init(data->ops, data);
> > +             if (ret < 0)
> > +                     goto out;
> > +     }
> > +
> > +     list_add_rcu(&data->list, &file->triggers);
> > +     ret++;
> > +
> > +     update_cond_flag(file);
> > +     if (trace_event_trigger_enable_disable(file, 1) < 0) {
> > +             list_del_rcu(&data->list);
> > +             update_cond_flag(file);
> > +             ret--;
> > +     }
> > +     init_trace_object();
> > +out:
> > +     return ret;
> > +}
> > +
> > +static void unregister_object_trigger(char *glob, struct event_trigger_ops *ops,
> > +                            struct event_trigger_data *test,
> > +                            struct trace_event_file *file)
> > +{
> > +     struct event_trigger_data *data;
> > +     bool unregistered = false;
> > +
> > +     lockdep_assert_held(&event_mutex);
> > +
> > +     list_for_each_entry(data, &file->triggers, list) {
> > +             if (data->cmd_ops->trigger_type == test->cmd_ops->trigger_type) {
> > +                     unregistered = true;
> > +                     list_del_rcu(&data->list);
> > +                     trace_event_trigger_enable_disable(file, 0);
> > +                     update_cond_flag(file);
> > +                     break;
> > +             }
> > +     }
> > +
> > +     if (unregistered && data->ops->free) {
> > +             data->ops->free(data->ops, data);
> > +             exit_trace_object();
> > +     }
>
> isn't this the following? Can you skip exit_trace_object()
> if data->ops->free == NULL?
>
>         if (unregistered) {
>                 if (data->ops->free)
>                         data->ops->free(data->ops, data);
>                 exit_trace_object();
>         }

Thanks, this one would be better, although data->ops->free  is not
empty at the moment.

>
> Thank you,
>
>
> > +}
> > +
> > +static int
> > +event_object_trigger_callback(struct event_command *cmd_ops,
> > +                    struct trace_event_file *file,
> > +                    char *glob, char *cmd, char *param)
> > +{
> > +     struct event_trigger_data *trigger_data;
> > +     struct event_trigger_ops *trigger_ops;
> > +     struct trace_event_call *call;
> > +     struct ftrace_event_field *field;
> > +     char *objtrace_cmd;
> > +     char *trigger = NULL;
> > +     char *arg;
> > +     char *number;
> > +     int ret;
> > +
> > +     ret = -EINVAL;
> > +     if (!param)
> > +             goto out;
> > +
> > +     /* separate the trigger from the filter (c:a:n [if filter]) */
> > +     trigger = strsep(&param, " \t");
> > +     if (!trigger)
> > +             goto out;
> > +     if (param) {
> > +             param = skip_spaces(param);
> > +             if (!*param)
> > +                     param = NULL;
> > +     }
> > +
> > +     objtrace_cmd = strsep(&trigger, ":");
> > +     if (!objtrace_cmd || strcmp(objtrace_cmd, "add"))
> > +             goto out;
> > +
> > +     arg = strsep(&trigger, ":");
> > +     if (!arg)
> > +             goto out;
> > +     call = file->event_call;
> > +     field = trace_find_event_field(call, arg);
> > +     if (!field)
> > +             goto out;
> > +
> > +     if (field->size != sizeof(void *))
> > +             goto out;
> > +
> > +     trigger_ops = cmd_ops->get_trigger_ops(cmd, trigger);
> > +
> > +     ret = -ENOMEM;
> > +     trigger_data = kzalloc(sizeof(*trigger_data), GFP_KERNEL);
> > +     if (!trigger_data)
> > +             goto out;
> > +
> > +     trigger_data->count = -1;
> > +     trigger_data->ops = trigger_ops;
> > +     trigger_data->cmd_ops = cmd_ops;
> > +     trigger_data->private_data = field;
> > +     INIT_LIST_HEAD(&trigger_data->list);
> > +     INIT_LIST_HEAD(&trigger_data->named_list);
> > +
> > +     if (glob[0] == '!') {
> > +             cmd_ops->unreg(glob+1, trigger_ops, trigger_data, file);
> > +             kfree(trigger_data);
> > +             ret = 0;
> > +             goto out;
> > +     }
> > +
> > +     if (trigger) {
> > +             number = strsep(&trigger, ":");
> > +
> > +             ret = -EINVAL;
> > +             if (!strlen(number))
> > +                     goto out_free;
> > +
> > +             /*
> > +              * We use the callback data field (which is a pointer)
> > +              * as our counter.
> > +              */
> > +             ret = kstrtoul(number, 0, &trigger_data->count);
> > +             if (ret)
> > +                     goto out_free;
> > +     }
> > +
> > +     if (!param) /* if param is non-empty, it's supposed to be a filter */
> > +             goto out_reg;
> > +
> > +     if (!cmd_ops->set_filter)
> > +             goto out_reg;
> > +
> > +     ret = cmd_ops->set_filter(param, trigger_data, file);
> > +     if (ret < 0)
> > +             goto out_free;
> > +
> > + out_reg:
> > +     /* Up the trigger_data count to make sure reg doesn't free it on failure */
> > +     event_object_trigger_init(trigger_ops, trigger_data);
> > +     ret = cmd_ops->reg(glob, trigger_ops, trigger_data, file);
> > +     /*
> > +      * The above returns on success the # of functions enabled,
> > +      * but if it didn't find any functions it returns zero.
> > +      * Consider no functions a failure too.
> > +      */
> > +     if (!ret) {
> > +             cmd_ops->unreg(glob, trigger_ops, trigger_data, file);
> > +             ret = -ENOENT;
> > +     } else if (ret > 0)
> > +             ret = 0;
> > +
> > +     /* Down the counter of trigger_data or free it if not used anymore */
> > +     trace_object_trigger_free(trigger_ops, trigger_data);
> > + out:
> > +     return ret;
> > +
> > + out_free:
> > +     if (cmd_ops->set_filter)
> > +             cmd_ops->set_filter(NULL, trigger_data, NULL);
> > +     kfree(trigger_data);
> > +     goto out;
> > +}
> > +
> > +static struct event_command trigger_object_cmd = {
> > +     .name                   = "objtrace",
> > +     .trigger_type           = ETT_TRACE_OBJECT,
> > +     .flags                  = EVENT_CMD_FL_NEEDS_REC,
> > +     .func                   = event_object_trigger_callback,
> > +     .reg                    = register_object_trigger,
> > +     .unreg                  = unregister_object_trigger,
> > +     .get_trigger_ops        = objecttrace_get_trigger_ops,
> > +     .set_filter             = set_trigger_filter,
> > +};
> > +
> > +__init int register_trigger_object_cmd(void)
> > +{
> > +     int ret;
> > +
> > +     ret = register_event_command(&trigger_object_cmd);
> > +     WARN_ON(ret < 0);
> > +
> > +     return ret;
> > +}
> > +
> > +static int init_trace_object(void)
> > +{
> > +     int ret;
> > +
> > +     if (atomic_inc_return(&trace_object_ref) != 1) {
> > +             ret = 0;
> > +             goto out;
> > +     }
> > +
> > +     ret = init_object_pool();
> > +     if (ret)
> > +             goto out;
> > +
> > +     event_trace_file.tr = top_trace_array();
> > +     if (WARN_ON(!event_trace_file.tr)) {
> > +             ret = -1;
> > +             goto out;
> > +     }
> > +     ret = register_ftrace_function(&trace_ops);
> > +out:
> > +     return ret;
> > +}
> > +
> > +static int exit_trace_object(void)
> > +{
> > +     int ret;
> > +
> > +     if (WARN_ON_ONCE(atomic_read(&trace_object_ref) <= 0))
> > +             goto out;
> > +
> > +     if (atomic_dec_return(&trace_object_ref) != 0) {
> > +             ret = 0;
> > +             goto out;
> > +     }
> > +
> > +     ret = unregister_ftrace_function(&trace_ops);
> > +     if (ret) {
> > +             pr_err("can't unregister ftrace for trace object\n");
> > +             goto out;
> > +     }
> > +     free_object_pool();
> > +out:
> > +     return ret;
> > +}
> > diff --git a/kernel/trace/trace_output.c b/kernel/trace/trace_output.c
> > index 3547e7176ff7..d747aed27104 100644
> > --- a/kernel/trace/trace_output.c
> > +++ b/kernel/trace/trace_output.c
> > @@ -1543,6 +1543,45 @@ static struct trace_event trace_func_repeats_event = {
> >       .funcs          = &trace_func_repeats_funcs,
> >  };
> >
> > +/* TRACE_OBJECT */
> > +static enum print_line_t trace_object_print(struct trace_iterator *iter, int flags,
> > +                                     struct trace_event *event)
> > +{
> > +     struct trace_object_entry *field;
> > +     struct trace_seq *s = &iter->seq;
> > +
> > +     trace_assign_type(field, iter->ent);
> > +     print_fn_trace(s, field->ip, field->parent_ip, flags);
> > +     trace_seq_printf(s, " object:0x%lx", field->object);
> > +     trace_seq_putc(s, '\n');
> > +
> > +     return trace_handle_return(s);
> > +}
> > +
> > +static enum print_line_t trace_object_raw(struct trace_iterator *iter, int flags,
> > +                                   struct trace_event *event)
> > +{
> > +     struct trace_object_entry *field;
> > +
> > +     trace_assign_type(field, iter->ent);
> > +
> > +     trace_seq_printf(&iter->seq, "%lx %lx\n",
> > +                      field->ip,
> > +                      field->parent_ip);
> > +
> > +     return trace_handle_return(&iter->seq);
> > +}
> > +
> > +static struct trace_event_functions trace_object_funcs = {
> > +     .trace          = trace_object_print,
> > +     .raw            = trace_object_raw,
> > +};
> > +
> > +static struct trace_event trace_object_event = {
> > +     .type           = TRACE_OBJECT,
> > +     .funcs          = &trace_object_funcs,
> > +};
> > +
> >  static struct trace_event *events[] __initdata = {
> >       &trace_fn_event,
> >       &trace_ctx_event,
> > @@ -1557,6 +1596,7 @@ static struct trace_event *events[] __initdata = {
> >       &trace_timerlat_event,
> >       &trace_raw_data_event,
> >       &trace_func_repeats_event,
> > +     &trace_object_event,
> >       NULL
> >  };
> >
> > --
> > 2.25.1
> >
>
>
> --
> Masami Hiramatsu <mhiramat@...nel.org>

---
JeffXie

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