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Message-Id: <20250902230204.f3e81b03e7f6805caba1b717@kernel.org> Date: Tue, 2 Sep 2025 23:02:04 +0900 From: Masami Hiramatsu (Google) <mhiramat@...nel.org> To: Jinchao Wang <wangjinchao600@...il.com> Cc: Steven Rostedt <rostedt@...dmis.org>, Peter Zijlstra <peterz@...radead.org>, Ingo Molnar <mingo@...nel.org>, x86@...nel.org, Mathieu Desnoyers <mathieu.desnoyers@...icios.com>, Thomas Gleixner <tglx@...utronix.de>, Borislav Petkov <bp@...en8.de>, Dave Hansen <dave.hansen@...ux.intel.com>, "H . Peter Anvin" <hpa@...or.com>, Alexander Shishkin <alexander.shishkin@...ux.intel.com>, Ian Rogers <irogers@...gle.com>, linux-kernel@...r.kernel.org, linux-trace-kernel@...r.kernel.org, linux-doc@...r.kernel.org, linux-perf-users@...r.kernel.org, "Masami Hiramatsu (Google)" <mhiramat@...nel.org> Subject: Re: [RFC PATCH 0/6] tracing: wprobe: Add wprobe for watchpoint (Adding Jinchao) On Mon, 1 Sep 2025 23:44:35 +0900 "Masami Hiramatsu (Google)" <mhiramat@...nel.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@...fies: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@...nel.org> -- Masami Hiramatsu (Google) <mhiramat@...nel.org>
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