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Date:   Mon, 31 Jan 2022 20:02:47 +0900
From:   Masami Hiramatsu <mhiramat@kernel.org>
To:     Jeff Xie <xiehuan09@gmail.com>
Cc:     rostedt@goodmis.org, mhiramat@kernel.org, mingo@redhat.com,
        zanussi@kernel.org, linux-kernel@vger.kernel.org
Subject: Re: [PATCH v8 0/4] trace: Introduce objtrace trigger to trace the
 kernel object
Message-Id: <20220131200247.4c49cc9a6056cc28afa1cd13@kernel.org>
In-Reply-To: <20220130144430.453221-1-xiehuan09@gmail.com>
References: <20220130144430.453221-1-xiehuan09@gmail.com>
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Hi Jeff,

Thank you for updating the series, I'm testing the series and found some
issues. See below;

On Sun, 30 Jan 2022 22:44:26 +0800
Jeff Xie <xiehuan09@gmail.com> wrote:

> Introduce a method based on function tracer to trace any object and get
> the value of the object dynamically. the object can be obtained from the
> dynamic event (kprobe_event/uprobe_event) or the static event(tracepoint).
> 
> Usage:
> When using the kprobe event, only need to set the objtrace(a new trigger),
> we can get the value of the object. The object is from the setting of the 
> kprobe event.
> 
> For example:
> For the function bio_add_page():
> 
> int bio_add_page(struct bio *bio, struct page *page,
> 	unsigned int len, unsigned int offset)
> 
> Firstly, we can set the base of the object, thus the first string "arg1"
> stands for the value of the first parameter of this function bio_add_gage(),
> 
> # echo 'p bio_add_page arg1=$arg1' > ./kprobe_events
> 
> Secondly, we can get the value dynamically based on above object. 
> 
> find the offset of the bi_size in struct bio:
> $ gdb vmlinux
> (gdb) p &(((struct bio *)0)->bi_iter.bi_size)
> $1 = (unsigned int *) 0x28
> 
> # echo 'objtrace:add:arg1,0x28:u32:1 if comm == "cat"' > ./events/kprobes/ \
> 	p_bio_add_page_0/trigger
> 
> # cd /sys/kernel/debug/tracing/
> # echo 'p bio_add_page arg1=$arg1' > ./kprobe_events
> # echo 'objtrace:add:arg1,0x28:u32:1 if comm == "cat"' > ./events/kprobes/p_bio_add_page_0/trigger

So doing after this command, I dumped the trigger file.

# cat events/kprobes/p_bio_add_page_0/trigger 
objtrace:count=1 if comm == "cat"

This is not correct. All the parameters are dropped. Thus I can not
remove the trigger without knowing the original command.

# echo '!objtrace:count=1 if comm == "cat"' >> ./events/kprobes/p_bio_add_page_0/trigger
sh: write error: Invalid argument

And there are another minor issue is here;

 # cd /sys/kernel/debug/tracing/
 # echo 'p bio_add_page $arg1 $arg2' > ./kprobe_events
 # echo 'objtrace:add:arg1,0x28:u32:1 if comm == "cat"' > ./events/kprobes/p_bio_add_page_0/trigger
 # echo '!objtrace:add:arg2' >> events/kprobes/p_bio_add_page_0/trigger 

Here, if I passed the "!objtrace:add:<a-field-exists-on-event>" then the objtrace
trigger was removed. But as you can see, the parameter is different.
Anyway, this is a minor issue, since we don't support multiple objtrace trigger
on the same event.

Could you fix these issues (and update the test case to check this?)

Thank you,

> 
> # du -sh /test.txt
> 12.0K   /test.txt
> 
> # cat  /test.txt > /dev/null
> # cat ./trace
> # tracer: nop
> #
> # entries-in-buffer/entries-written: 128/128   #P:4
> #
> #                                _-----=> irqs-off/BH-disabled
> #                               / _----=> need-resched
> #                              | / _---=> hardirq/softirq
> #                              || / _--=> preempt-depth
> #                              ||| / _-=> migrate-disable
> #                              |||| /     delay
> #           TASK-PID     CPU#  |||||  TIMESTAMP  FUNCTION
> #              | |         |   |||||     |         |
>              cat-117     [002] ...1.     1.602243: __bio_try_merge_page <-bio_add_page object:0xffff88811bee4000 value:0x0
>              cat-117     [002] ...1.     1.602244: __bio_add_page <-bio_add_page object:0xffff88811bee4000 value:0x0
>              cat-117     [002] ...2.     1.602244: bio_add_page <-ext4_mpage_readpages object:0xffff88811bee4000 value:0x1000
>              cat-117     [002] ...1.     1.602245: __bio_try_merge_page <-bio_add_page object:0xffff88811bee4000 value:0x1000
>              cat-117     [002] ...1.     1.602245: __bio_add_page <-bio_add_page object:0xffff88811bee4000 value:0x1000
>              cat-117     [002] ...2.     1.602245: bio_add_page <-ext4_mpage_readpages object:0xffff88811bee4000 value:0x2000
>              cat-117     [002] ...1.     1.602245: __bio_try_merge_page <-bio_add_page object:0xffff88811bee4000 value:0x2000
>              cat-117     [002] ...1.     1.602245: __bio_add_page <-bio_add_page object:0xffff88811bee4000 value:0x2000
>              cat-117     [002] ...1.     1.602245: submit_bio <-ext4_mpage_readpages object:0xffff88811bee4000 value:0x3000
>              cat-117     [002] ...1.     1.602245: submit_bio_noacct <-ext4_mpage_readpages object:0xffff88811bee4000 value:0x3000
>              cat-117     [002] ...1.     1.602246: __submit_bio <-submit_bio_noacct object:0xffff88811bee4000 value:0x3000
>              cat-117     [002] ...1.     1.602246: submit_bio_checks <-__submit_bio object:0xffff88811bee4000 value:0x3000
>              cat-117     [002] ...1.     1.602246: __cond_resched <-submit_bio_checks object:0xffff88811bee4000 value:0x3000
>              cat-117     [002] ...1.     1.602246: should_fail_bio <-submit_bio_checks object:0xffff88811bee4000 value:0x3000
>              cat-117     [002] ...1.     1.602246: blk_mq_submit_bio <-submit_bio_noacct object:0xffff88811bee4000 value:0x3000
>              cat-117     [002] ...1.     1.602246: blk_attempt_plug_merge <-blk_mq_submit_bio object:0xffff88811bee4000 value:0x3000
>              cat-117     [002] ...1.     1.602246: blk_mq_sched_bio_merge <-blk_mq_submit_bio object:0xffff88811bee4000 value:0x3000
>              cat-117     [002] ...1.     1.602247: __rcu_read_lock <-blk_mq_submit_bio object:0xffff88811bee4000 value:0x3000
>              cat-117     [002] ...1.     1.602247: __rcu_read_unlock <-blk_mq_submit_bio object:0xffff88811bee4000 value:0x3000
>              cat-117     [002] ...1.     1.602247: __blk_mq_alloc_requests <-blk_mq_submit_bio object:0xffff88811bee4000 value:0x3000
>           <idle>-0       [002] d..3.     1.602298: bio_endio <-blk_update_request object:0xffff88811bee4000 value:0x0
>           <idle>-0       [002] d..3.     1.602298: mpage_end_io <-blk_update_request object:0xffff88811bee4000 value:0x0
>           <idle>-0       [002] d..3.     1.602298: __read_end_io <-blk_update_request object:0xffff88811bee4000 value:0x0
>           <idle>-0       [002] d..3.     1.602300: bio_put <-blk_update_request object:0xffff88811bee4000 value:0x0
>           <idle>-0       [002] d..3.     1.602300: bio_free <-blk_update_request object:0xffff88811bee4000 value:0x0
>           <idle>-0       [002] d..3.     1.602300: mempool_free <-blk_update_request object:0xffff88811bee4000 value:0x0
>           <idle>-0       [002] d..3.     1.602300: mempool_free_slab <-blk_update_request object:0xffff88811bee4000 value:0x0
>           <idle>-0       [002] d..3.     1.602300: kmem_cache_free <-blk_update_request object:0xffff88811bee4000 value:0x0
> 	  ...
> 
> Almost all changelogs were suggested by Masami(mhiramat@kernel.org)
> and steve(rostedt@goodmis.org), thank you all so much.
> 
> v8:
> - revert to use per-cpu recursion for the function trace_object_events_call
> - recover the filter when getting the value of the object
> - simplify the implementation for the function get_object_value
> - fix the build error
> 
> v7:
> - use fixed-size array for object pool instead of list structure
> - use ftrace_test_recursion_trylock for function trace hook function
> - fix trace_object_ref reference count in the init_trace_object
> - invoke exit_trace_object no matter whether data->ops->free is null 
>   in the unregister_object_trigger
> - release private_data of event_trigger_data in the trace_object_trigger_free
> - remove [RFC] tag
> 
> v6:
> - change the objtrace trigger syntax.
> - add patchset description
> - add <tracefs>/README
> 
> v5:
> - add testcasts
> - add check the field->size
> - add lockless to search object
> - describe the object trace more clearly in Kconfig
> 
> v4:
> - please ignore the v4 which is the same as v3
> 
> v3:
> - change the objfilter to objtrace
> - add a command to the objfilter syntax
> - change to get the value of the object
> - use trace_find_event_field to find the field instead of using argN
> - get data from @rec in the event trigger callback funciton
> 
> v2:
> - adding a "objfilter" trigger to update object
> 
> 
> Jeff Xie (4):
>   trace: Add trace any kernel object
>   trace/objtrace: get the value of the object
>   trace/objtrace: Add testcases for objtrace
>   trace/objtrace: Add documentation for objtrace
> 
>  Documentation/trace/events.rst                |  83 +++
>  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                  |  18 +
>  kernel/trace/trace_events_trigger.c           |   1 +
>  kernel/trace/trace_object.c                   | 631 ++++++++++++++++++
>  kernel/trace/trace_output.c                   |  40 ++
>  .../ftrace/test.d/trigger/trigger-objtrace.tc |  39 ++
>  11 files changed, 835 insertions(+)
>  create mode 100644 kernel/trace/trace_object.c
>  create mode 100644 tools/testing/selftests/ftrace/test.d/trigger/trigger-objtrace.tc
> 
> -- 
> 2.25.1
> 


-- 
Masami Hiramatsu <mhiramat@kernel.org>