Re: [PATCH v9 1/4] trace: Add trace any kernel object

[Jeff Xie <xiehuan09@gmail.com>]

Hi steve,

Thank you for your patient review.

On Tue, Apr 19, 2022 at 10:14 AM Steven Rostedt <rostedt@goodmis.org> wrote:
>
> On Fri,  4 Feb 2022 11:56:41 +0800
> Jeff Xie <xiehuan09@gmail.com> wrote:
>
> > 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.
> >
> > Syntax:
> >       objtrace:add:obj[:count][if <filter>]
> >
> > Usage:
> >       # echo 'p bio_add_page arg1=$arg1' > kprobe_events
> >       # cd events/kprobes/p_bio_add_page_0
> >       # echo 'objtrace:add:arg1:1 if comm == "cat"' > ./trigger
> >       # cat /test.txt
>
> OK, so patch one only does the object and not the more useful "value"
> field. That comes in patch 2.

Yes, the  "value" is included in patch 2.

>
> >
> > Signed-off-by: Jeff Xie <xiehuan09@gmail.com>
> > ---
> >  include/linux/trace_events.h        |   1 +
> >  kernel/trace/Kconfig                |  10 +
> >  kernel/trace/Makefile               |   1 +
> >  kernel/trace/trace.c                |   3 +
> >  kernel/trace/trace.h                |   8 +
> >  kernel/trace/trace_entries.h        |  17 +
> >  kernel/trace/trace_events_trigger.c |   1 +
> >  kernel/trace/trace_object.c         | 515 ++++++++++++++++++++++++++++
> >  kernel/trace/trace_output.c         |  40 +++
> >  9 files changed, 596 insertions(+)
> >  create mode 100644 kernel/trace/trace_object.c
> >
> > diff --git a/include/linux/trace_events.h b/include/linux/trace_events.h
> > index 70c069aef02c..3ccdbc1d25dd 100644
> > --- a/include/linux/trace_events.h
> > +++ b/include/linux/trace_events.h
> > @@ -685,6 +685,7 @@ 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 a5eb5e7fd624..c51b7eb1508d 100644
> > --- a/kernel/trace/Kconfig
> > +++ b/kernel/trace/Kconfig
> > @@ -250,6 +250,16 @@ 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.c b/kernel/trace/trace.c
> > index a734d5ae34c8..b4513c2bbd52 100644
> > --- a/kernel/trace/trace.c
> > +++ b/kernel/trace/trace.c
> > @@ -5605,6 +5605,9 @@ static const char readme_msg[] =
> >       "\t            enable_hist:<system>:<event>\n"
> >       "\t            disable_hist:<system>:<event>\n"
> >  #endif
> > +#ifdef CONFIG_TRACE_OBJECT
> > +     "\t            objtrace:add:obj[:count][if <filter>]\n"
> > +#endif
> >  #ifdef CONFIG_STACKTRACE
> >       "\t\t    stacktrace\n"
> >  #endif
> > diff --git a/kernel/trace/trace.h b/kernel/trace/trace.h
> > index 0f5e22238cd2..8b66515a36d5 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,
> >  };
> > @@ -472,6 +473,7 @@ 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)
> >
> > @@ -1537,6 +1539,12 @@ 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 d00fee705f9c..c3371a6902af 100644
> > --- a/kernel/trace/trace_events_trigger.c
> > +++ b/kernel/trace/trace_events_trigger.c
> > @@ -2025,6 +2025,7 @@ __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..540e387c613a
> > --- /dev/null
> > +++ b/kernel/trace/trace_object.c
> > @@ -0,0 +1,515 @@
> > +// SPDX-License-Identifier: GPL-2.0
> > +/*
> > + * trace the kernel object in the kernel function parameter
> > + * Copyright (C) 2021 Jeff Xie <xiehuan09@gmail.com>
> > + */
> > +
> > +#define pr_fmt(fmt) "trace_object: " fmt
> > +
> > +#include "trace_output.h"
> > +
> > +#define MAX_TRACED_OBJECT 5
> > +#define OBJTRACE_CMD_LEN  10
>
> The len should at least be a multiple of word size. 16?

Thanks for your suggestion, maybe 16 would be better, I will redefine this size.

>
> > +static DEFINE_PER_CPU(unsigned int, trace_object_event_disable);
> > +static DEFINE_RAW_SPINLOCK(trace_obj_lock);
> > +static struct trace_event_file event_trace_file;
>
> You do not want to use a global "event_trace_file". And the writes
> should be done in the instance (trace_array) that the trigger was added
> to. That is, if someone does:
>
>   # mkdir instances/foo
>   # echo 'objtrace:add:arg1:1 if comm == "cat"' > instances/foo/events/kprobes/p_bio_add_page_0/trigger
>
> Then the tracing should happen in the instance/foo/trace and not at the
> toplevel trace file.

I will rethink how to use the event_trace_file, I ignored the use of
"instance" ;-)

> > +static const int max_args_num = 6;
> > +static atomic_t trace_object_ref;
> > +static atomic_t num_traced_obj;
> > +static int exit_trace_object(void);
> > +static int init_trace_object(void);
> > +
> > +static struct object_instance {
> > +     void *obj;
>
> Either have a pointer to the trace_array that the object is for here,
> or we can have each trace array have a max of 5 objects and add it to
> the trace_array when it is created.

Thanks. I will fix it.

> > +} traced_obj[MAX_TRACED_OBJECT];
> > +
> > +/* objtrace private data */
> > +struct objtrace_trigger_data {
> > +     struct ftrace_event_field *field;
> > +     char objtrace_cmd[OBJTRACE_CMD_LEN];
> > +};
> > +
> > +static bool object_exist(void *obj)
> > +{
> > +     int i, max;
> > +
> > +     max = atomic_read(&num_traced_obj);
> > +     smp_rmb();
> > +     for (i = 0; i < max; i++) {
> > +             if (traced_obj[i].obj == obj)
> > +                     return true;
> > +     }
> > +     return false;
> > +}
> > +
> > +static bool object_empty(void)
> > +{
> > +     return !atomic_read(&num_traced_obj);
> > +}
> > +
> > +static void set_trace_object(void *obj)
> > +{
> > +     unsigned long flags;
> > +
> > +     if (in_nmi())
> > +             return;
> > +
> > +     if (!obj)
> > +             return;
> > +
> > +     if (object_exist(obj))
> > +             return;
> > +
> > +     /* only this place has write operations */
> > +     raw_spin_lock_irqsave(&trace_obj_lock, flags);
> > +     if (atomic_read(&num_traced_obj) == MAX_TRACED_OBJECT) {
> > +             trace_printk("object_pool is full, can't trace object:0x%px\n", obj);
>
> You can't use trace_printk(). That will trigger a nasty message in
> dmesg. You can use trace_array_printk_buf() instead.

Thanks for your guidance.

>
> > +             goto out;
> > +     }
> > +     traced_obj[atomic_read(&num_traced_obj)].obj = obj;
> > +     /* make sure the num_traced_obj update always appears after traced_obj update */
> > +     smp_wmb();
> > +     atomic_inc(&num_traced_obj);
> > +out:
> > +     raw_spin_unlock_irqrestore(&trace_obj_lock, flags);
> > +}
> > +
> > +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);
>
> We should not be using trace_event_buffer_lock_reserver() here, as it
> is expected to be done for trace events, not unique data like this.
> This is more like the function tracer, and use
> trace_buffer_lock_reserve() instead.

Yes, It looks like this trace_buffer_lock_reserve() should indeed be
used in this place.

>
> > +     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)
> > +{
>
> So the op can hold data, which we should allocate it so that there is
> one ftrace_ops per trace_array (like function tracing does). May need
> callbacks from mkdir and rmdir in trace.c. But the trace_array (tr)
> will hold the buffer you want to write to. Or at the very least, the
> object can hold it.

Thanks, I will  dig into this detail ;-)

>
> > +     struct pt_regs *pt_regs = ftrace_get_regs(fregs);
> > +     unsigned long obj;
> > +     unsigned int disabled;
> > +     int n;
> > +
> > +     preempt_disable_notrace();
> > +
> > +     disabled = this_cpu_inc_return(trace_object_event_disable);
>
> If we make this list per instance, we will only want to disable the
> instance.

Thanks, I will fix this.

> > +     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);
> > +     /* The parameters of a function may match multiple objects */
> > +     }
> > +out:
> > +     this_cpu_dec(trace_object_event_disable);
> > +     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 objtrace_trigger_data *obj_data = data->private_data;
> > +     struct ftrace_event_field *field;
> > +     void *obj = NULL;
> > +
> > +     field = obj_data->field;
> > +     memcpy(&obj, rec + field->offset, sizeof(obj));
> > +     set_trace_object(obj);
> > +}
> > +
> > +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) {
> > +             kfree(data->private_data);
> > +             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);
> > +}
> > +
> > +static int event_object_trigger_init(struct event_trigger_ops *ops,
> > +                    struct event_trigger_data *data)
> > +{
> > +     data->ref++;
> > +     return 0;
> > +}
> > +
> > +static int
> > +event_trigger_print(const char *name, struct seq_file *m,
> > +             void *data, char *filter_str, void *objtrace_data)
> > +{
> > +     long count = (long)data;
> > +     struct objtrace_trigger_data *obj_data = objtrace_data;
> > +
> > +     seq_puts(m, name);
> > +
> > +     seq_printf(m, ":%s", obj_data->objtrace_cmd);
> > +     seq_printf(m, ":%s", obj_data->field->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, data->private_data);
> > +}
> > +
> > +static struct event_trigger_ops objecttrace_trigger_ops = {
> > +     .trigger                = 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 = {
> > +     .trigger                = 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_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;
>
> This should just be "return -EEXIST", but you probably just copied this
> from register_trigger() which does it like this as well. I'll need to
> go fix that.
>
> > +                     goto out;
> > +             }
> > +     }
> > +
> > +     if (data->ops->init) {
> > +             ret = data->ops->init(data->ops, data);
> > +             if (ret < 0)
>
>                         return ret;
>
> works too, but again, this is just a copy of an existing function that
> has the useless goto as well.
>
> > +                     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--;
> > +     }
>
> OK, so this is pretty much identical to "register_tigger()" in
> trace_events_trigger() except for the init below. We should probably
> just make the register_trigger() global and reuse it here.
>
> > +     init_trace_object();
> > +out:
> > +     return ret;
> > +}
> > +
> > +static void unregister_object_trigger(char *glob,
> > +                            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) {
> > +             if (data->ops->free)
> > +                     data->ops->free(data->ops, data);
> > +             exit_trace_object();
> > +     }
> > +}
> > +
> > +static bool field_exist(struct trace_event_file *file,
> > +                     struct event_command *cmd_ops,
> > +                     const char *field_name)
> > +{
> > +     struct event_trigger_data *data;
> > +     struct objtrace_trigger_data *obj_data;
> > +
> > +     lockdep_assert_held(&event_mutex);
> > +
> > +     list_for_each_entry(data, &file->triggers, list) {
> > +             if (data->cmd_ops->trigger_type == cmd_ops->trigger_type) {
> > +                     obj_data = data->private_data;
> > +                     if (!strcmp(obj_data->field->name, field_name))
> > +                             return true;
> > +             }
> > +     }
> > +
> > +     return false;
> > +}
> > +
> > +static int
> > +event_object_trigger_parse(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 objtrace_trigger_data *obj_data;
> > +     struct trace_event_call *call;
> > +     struct ftrace_event_field *field;
> > +     char *objtrace_cmd;
> > +     char *trigger = NULL;
> > +     char *arg;
> > +     char *number;
> > +     int ret;
> > +     bool remove = false;
> > +
> > +     ret = -EINVAL;
> > +     if (!param)
> > +             goto out;
>
> So this is also copied mostly from event_tigger_parse, and has the
> unneeded gotos as well.
>
> We need to consolidate the code a bit, and add helper functions to
> share between them, instead of just cut and pasting and tweaking.
> That's a maintenance nightmare.
>
> > +
> > +     /* 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;
>
> We need to add error messages to write to the error log when things
> like this fail. Users will have no idea what happened.

Yes, I will add some error logs.

>
> > +
> > +     if (glob[0] == '!')
> > +             remove = true;
> > +
> > +     if (remove && !field_exist(file, cmd_ops, field->name))
> > +     goto out;
>
> Bad indentation.
>
> > +     trigger_ops = cmd_ops->get_trigger_ops(cmd, trigger);
> > +     ret = -ENOMEM;
> > +     obj_data = kzalloc(sizeof(*obj_data), GFP_KERNEL);
> > +     if (!obj_data)
> > +             goto out;
> > +     obj_data->field = field;
> > +     snprintf(obj_data->objtrace_cmd, OBJTRACE_CMD_LEN, objtrace_cmd);
> > +
> > +     trigger_data = kzalloc(sizeof(*trigger_data), GFP_KERNEL);
> > +     if (!trigger_data) {
> > +             kfree(obj_data);
> > +             goto out;
> > +     }
> > +
> > +     trigger_data->count = -1;
> > +     trigger_data->ops = trigger_ops;
> > +     trigger_data->cmd_ops = cmd_ops;
> > +     trigger_data->private_data = obj_data;
> > +     INIT_LIST_HEAD(&trigger_data->list);
> > +     INIT_LIST_HEAD(&trigger_data->named_list);
> > +
> > +     if (remove) {
> > +             cmd_ops->unreg(glob+1, trigger_data, file);
> > +             kfree(obj_data);
> > +             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_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_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(obj_data);
> > +     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,
> > +     .parse                  = event_object_trigger_parse,
> > +     .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;
> > +     }
> > +
> > +     event_trace_file.tr = top_trace_array();
> > +     if (WARN_ON(!event_trace_file.tr)) {
> > +             ret = -1;
> > +             atomic_dec(&trace_object_ref);
> > +             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)) {
>
> No reason for the goto out. This shuold be:
>
>         if (WARN_ON_ONCE(atomic_read(&trace_object_ref) <= 0))
>                 return -1;
>
> > +             ret = -1;
> > +             goto out;
> > +     }
> > +
> > +     if (atomic_dec_return(&trace_object_ref) != 0) {
>
> And this:
>
>         if (atomic_dec_return(&trace_object_ref) != 0)
>                 return 0;
>
> goto's should only be used if there's something to be "undone". But I
> see you copied code that had this done incorrectly as well.

 Thanks for the detailed explanation, after I use Tom's code, I will
fix these goto.

> So that's my first pass at reviewing the code. It looks promising, but
> I think there's still a lot more to do to get it up to par with what is
> expected for the kernel.

Thank you for your very patient review, the kernel code is indeed very
high quality,
 I will try my best to complete this work well.

> -- Steve
>
>
> > +             ret = 0;
> > +             goto out;
> > +     }
> > +
> > +     ret = unregister_ftrace_function(&trace_ops);
> > +     if (ret) {
> > +             pr_err("can't unregister ftrace for trace object\n");
> > +             goto out;
> > +     }
> > +     atomic_set(&num_traced_obj, 0);
> > +out:
> > +     return ret;
> > +}
> > diff --git a/kernel/trace/trace_output.c b/kernel/trace/trace_output.c
> > index 8aa493d25c73..265428154638 100644
> > --- a/kernel/trace/trace_output.c
> > +++ b/kernel/trace/trace_output.c
> > @@ -1547,6 +1547,45 @@ 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,
> > @@ -1561,6 +1600,7 @@ static struct trace_event *events[] __initdata = {
> >       &trace_timerlat_event,
> >       &trace_raw_data_event,
> >       &trace_func_repeats_event,
> > +     &trace_object_event,
> >       NULL
> >  };
> >
>
---
JeffXie