On 9/2/25 22:02, Masami Hiramatsu (Google) wrote:
(Adding Jinchao)
On Mon, 1 Sep 2025 23:44:35 +0900
"Masami Hiramatsu (Google)" <mhiramat@xxxxxxxxxx> 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.
Hi, Masami
Thanks for including me. I only received the cover letter, so I'm
providing my feedback here:
- trigger_data issue:
it appears that the instance being removed is not the same as
the one that was originally set.
- the function call issue:
`trace_wprobe_update_local()` is called twice, once in the trigger
callback and again in `wprobe_work_func`.
I also noticed that the Watchpoint probe and KStackWatch implementations
share very similar logic for managing hardware breakpoints/watchpoints
(`hwbp/watch`):
- `watch_init(unsigned long &place_holder)`
- `watch_on(struct perf_event_attr *attr)`
- `watch_off()` (or reset to the `place_holder` value)
- `watch_uninit()`
Their primary difference lies in their handler functions, specifically
the `perf_overflow_handler_t triggered` callback.
I believe we could work together to unify this logic. I am open to
either approach: I can refactor my watch.c, or you can introduce new
helpers. This would help us save duplicated work and review time.
Thanks,
In this version, I reuse Jinchao's arch_reinstall_hw_breakpoint()
patch[1].
[1] https://lore.kernel.org/all/20250828073311.1116593-6-wangjinchao600@xxxxxxxxx/
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@xxxxxxxxxx>
--
Best regards,
Jinchao
