Re: [RFC PATCH 0/6] tracing: wprobe: Add wprobe for watchpoint

Masami Hiramatsu
2025-09-02T14:02:08Z

(Adding Jinchao)

On Mon, 1 Sep 2025 23:44:35 +0900
"Masami Hiramatsu (Google)" <mhiramat@kernel.org> wrote:

> Hi,
>
> Here is an RFC series for adding new wprobe (watch probe) which
> provides memory access tracing event. Moreover, this can be used via
> event trigger. Thus it can trace memory access on a dynamically
> allocated objects too.

BTW, this series is on the top of probes/for-next branch in the
linux-trace tree.

Thanks,

>
> In this version, I reuse Jinchao's arch_reinstall_hw_breakpoint()
> patch[1].
>
> [1] https://lore.kernel.org/all/20250828073311.1116593-6-wangjinchao600@gmail.com/
>
> The basic usage of this wprobe is similar to other probes;
>
> w:[GRP/][EVENT] [r|w|rw]@<ADDRESS|SYMBOL[+OFFS]> [FETCHARGS]
>
> This defines a new wprobe event. For example, to trace jiffies update,
> you can do;
>
> echo 'w:my_jiffies w@jiffies:8 value=+0($addr)' >> dynamic_events
> echo 1 > events/wprobes/my_jiffies/enable
>
> Moreover, this can be combined with event trigger to trace the memory
> accecss on slab objects. The trigger syntax is;
>
> set_wprobe:WPROBE_EVENT:FIELD[+ADJUST]
> clear_wprobe:WPROBE_EVENT
>
> For example, trace the first 8 byte of the dentry data structure passed
> to do_truncate() until it is deleted by __dentry_kill().
> (Note: all tracefs setup uses '>>' so that it does not kick do_truncate())
>
> # echo 'w:watch rw@0:8 address=$addr value=+0($addr)' > dynamic_events
>
> # echo 'f:truncate do_truncate dentry=$arg2' >> dynamic_events
> # echo 'set_wprobe:watch:dentry' >> events/fprobes/truncate/trigger
>
> # echo 'f:dentry_kill __dentry_kill dentry=$arg1' >> dynamic_events
> # echo 'clear_wprobe:watch' >> events/fprobes/dentry_kill/trigger
>
> # echo 1 >> events/fprobes/truncate/enable
> # echo 1 >> events/fprobes/dentry_kill/enable
>
> # echo aaa > /tmp/hoge
> # echo bbb > /tmp/hoge
> # echo ccc > /tmp/hoge
> # rm /tmp/hoge
>
> Then, the trace data will show;
>
> # tracer: nop
> #
> # entries-in-buffer/entries-written: 16/16 #P:8
> #
> # _-----=> irqs-off/BH-disabled
> # / _----=> need-resched
> # | / _---=> hardirq/softirq
> # || / _--=> preempt-depth
> # ||| / _-=> migrate-disable
> # |||| / delay
> # TASK-PID CPU# ||||| TIMESTAMP FUNCTION
> # [ 7.026136] sh (113) used greatest stack depth: 12912 bytes left
> | | | ||||| | |
> sh-113 [002] ..... 7.024402: truncate: (do_truncate+0x4/0x120) dentry=0xffff8880069194b8
> sh-113 [002] ..Zff 7.024822: watch: (lookup_fast+0xaa/0x150) address=0xffff8880069194b8 value=0x200008
> sh-113 [002] ..Zff 7.024830: watch: (step_into+0x82/0x360) address=0xffff8880069194b8 value=0x200008
> sh-113 [002] ..Zff 7.024834: watch: (step_into+0x9f/0x360) address=0xffff8880069194b8 value=0x200008
> sh-113 [002] ..Zff 7.024839: watch: (path_openat+0xb3a/0xe70) address=0xffff8880069194b8 value=0x200008
> sh-113 [002] ..Zff 7.024843: watch: (path_openat+0xb9a/0xe70) address=0xffff8880069194b8 value=0x200008
> sh-113 [002] ..... 7.024847: truncate: (do_truncate+0x4/0x120) dentry=0xffff8880069194b8
> sh-113 [002] ...1. 7.025364: dentry_kill: (__dentry_kill+0x0/0x220) dentry=0xffff888006919380
> sh-113 [002] ...1. 7.025511: dentry_kill: (__dentry_kill+0x0/0x220) dentry=0xffff8880069195f0
> rm-118 [003] ...1. 7.027543: dentry_kill: (__dentry_kill+0x0/0x220) dentry=0xffff8880069194b8
> sh-113 [002] ...2. 7.027825: dentry_kill: (__dentry_kill+0x0/0x220) dentry=0xffff8880044429c0
> sh-113 [002] ...2. 7.027833: dentry_kill: (__dentry_kill+0x0/0x220) dentry=0xffff888004442270
>
>
> Thank you,
>
> ---
>
> Jinchao Wang (1):
> x86/HWBP: introduce arch_reinstall_hw_breakpoint() for atomic context
>
> Masami Hiramatsu (Google) (5):
> tracing: wprobe: Add watchpoint probe event based on hardware breakpoint
> HWBP: Add modify_wide_hw_breakpoint_local() API
> tracing: wprobe: Add wprobe event trigger
> selftests: tracing: Add a basic testcase for wprobe
> selftests: tracing: Add syntax testcase for wprobe
>
>
> Documentation/trace/index.rst | 1
> Documentation/trace/wprobetrace.rst | 129 ++
> arch/Kconfig | 10
> arch/x86/Kconfig | 1
> arch/x86/include/asm/hw_breakpoint.h | 3
> arch/x86/kernel/hw_breakpoint.c | 61 +
> include/linux/hw_breakpoint.h | 6
> include/linux/trace_events.h | 3
> kernel/events/hw_breakpoint.c | 36 +
> kernel/trace/Kconfig | 24
> kernel/trace/Makefile | 1
> kernel/trace/trace.c | 9
> kernel/trace/trace.h | 5
> kernel/trace/trace_probe.c | 20
> kernel/trace/trace_probe.h | 8
> kernel/trace/trace_wprobe.c | 1111 ++++++++++++++++++++
> .../ftrace/test.d/dynevent/add_remove_wprobe.tc | 68 +
> .../test.d/dynevent/wprobes_syntax_errors.tc | 20
> 18 files changed, 1513 insertions(+), 3 deletions(-)
> create mode 100644 Documentation/trace/wprobetrace.rst
> create mode 100644 kernel/trace/trace_wprobe.c
> create mode 100644 tools/testing/selftests/ftrace/test.d/dynevent/add_remove_wprobe.tc
> create mode 100644 tools/testing/selftests/ftrace/test.d/dynevent/wprobes_syntax_errors.tc
>
> --
> Masami Hiramatsu (Google) <mhiramat@kernel.org>

--
Masami Hiramatsu (Google) <mhiramat@kernel.org>