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Date: Mon, 31 Jan 2022 20:02:47 +0900
From: Masami Hiramatsu <mhiramat@...nel.org>
To: Jeff Xie <xiehuan09@...il.com>
Cc: rostedt@...dmis.org, mhiramat@...nel.org, mingo@...hat.com,
zanussi@...nel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v8 0/4] trace: Introduce objtrace trigger to trace the
kernel object
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@...il.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@...nel.org)
> and steve(rostedt@...dmis.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@...nel.org>
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