[PATCH v11 00/11] tracing: wprobe: x86: Add wprobe for watchpoint
From: "Masami Hiramatsu (Google)" <mhiramat@kernel.org>
Date: 2026-08-02 08:18:32
Also in:
linux-doc, linux-perf-users, lkml
Hi, Here is the 11th version of the 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 dynamically allocated objects too. The previous version is here: https://lore.kernel.org/all/178476134787.26117.10094977293012760490.stgit@devnote2/ (local) The major changes in this version is to use Jinchao's new modify_local_hw_breakpoint_addr() API, add count option support to wprobe trigger, skip wprobe trigger during another wprobe trigger is working and rewrite selftests for wprobe trigger with trace-events-sample module. Changes in v11: - Updated hardware breakpoint modification API: - Replaced arch_reinstall_hw_breakpoint() with arch_modify_local_hw_breakpoint_addr() and modify_local_hw_breakpoint_addr() API. - Made DR7 updates NMI safe by using atomic cmpxchg for slot management and per-CPU sequence number (cpu_dr7_seq) to detect concurrent NMI updates. - Refactored wprobe trigger implementation: - Updated set_wprobe/clear_wprobe trigger to use modify_local_hw_breakpoint_addr(). - Added tracepoint_synchronize_unregister() in wprobe_unregister_trigger() and parse error path. - Added NULL check for tw->bp_event in trace_wprobe_update_local() to prevent race conditions. - Switched trigger data freeing to use event_trigger_data::private_data_free. - Added count option support (count=N) for wprobe triggers. - Fixed trigger address calculation (cast rec to char *). - Added work_pending flag to avoid update conflicts between CPUs. - Fixed wprobe_trigger_find_same() to check wprobe_data->clear flag. - Update trigger-wprobe*.tc to use trace-events-sample kernel module. - Fixed selftest: - Updated trigger-wprobe.tc assertion logic for clear_wprobe trigger test to check trace log instead of sysfs enable file (which remains 1 under soft-disable). Public branch ------------- I will push this branch as topic/wprobe-v2 to my tree so that it can be easily tested. https://git.kernel.org/pub/scm/linux/kernel/git/mhiramat/linux.git/log/?h=topic/wprobe-v2 This is based on linux-trace tree's probes/for-next. Usage ----- 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($addr)' >> dynamic_events echo 1 > events/wprobes/my_jiffies/enable Moreover, this can be combined with event trigger to trace the memory access on slab objects. The trigger syntax is; set_wprobe:WPROBE_EVENT:FIELD[+OFFSET] [if FILTER] clear_wprobe:WPROBE_EVENT[:FIELD[+OFFSET]] [if FILTER] set_wprobe sets WPROBE_EVENT's watch address on FIELD[+OFFSET]. clear_wprobe clears WPROBE_EVENT's watch address if it is set to FIELD[+OFFSET]. If FIELD is omitted, forcibly clear the watch address when trigger event is hit. For example, trace the first 8 byte of the dentry data structure passed to do_truncate() until it is deleted by dentry_kill(). (Note: all tracefs setup uses '>>' so that it does not kick do_truncate()) # echo 'w:watch rw@0:8 address=$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:dentry' >> 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: 32/32 #P:8 # # _-----=> irqs-off/BH-disabled # / _----=> need-resched # | / _---=> hardirq/softirq # || / _--=> preempt-depth # ||| / _-=> migrate-disable # |||| / delay # TASK-PID CPU# ||||| TIMESTAMP FUNCTION # | | | ||||| | | sh-107 [004] ...1. 9.990418: dentry_kill: (dentry_kill+0x0/0x2c0) dentry=0xffff888004ad6618 sh-107 [004] ...1. 9.990914: dentry_kill: (dentry_kill+0x0/0x2c0) dentry=0xffff888004b3de78 sh-107 [004] ...1. 9.993175: dentry_kill: (dentry_kill+0x0/0x2c0) dentry=0xffff8880049ddd40 sh-107 [004] ..... 9.995198: truncate: (do_truncate+0x4/0x120) dentry=0xffff8880048083a8 sh-107 [004] ...1. 9.995389: dentry_kill: (dentry_kill+0x0/0x2c0) dentry=0xffff8880049db998 sh-107 [004] ..Zff 9.997503: watch: (lookup_fast+0xaa/0x150) address=0xffff8880048083a8 value=0x8200080 sh-107 [004] ..Zff 9.997509: watch: (path_openat+0x211/0xda0) address=0xffff8880048083a8 value=0x8200080 sh-107 [004] ..Zff 9.997514: watch: (path_openat+0xa56/0xda0) address=0xffff8880048083a8 value=0x8200080 sh-107 [004] ..Zff 9.997518: watch: (path_openat+0xae2/0xda0) address=0xffff8880048083a8 value=0x8200080 sh-107 [004] ..... 9.997521: truncate: (do_truncate+0x4/0x120) dentry=0xffff8880048083a8 sh-107 [004] ...1. 9.997582: dentry_kill: (dentry_kill+0x0/0x2c0) dentry=0xffff888004808270 sh-107 [004] ...1. 9.999365: dentry_kill: (dentry_kill+0x0/0x2c0) dentry=0xffff8880049db728 sh-107 [004] ...1. 9.999388: dentry_kill: (dentry_kill+0x0/0x2c0) dentry=0xffff888004b1c000 rm-113 [005] ..Zff 10.000965: watch: (lookup_fast+0xaa/0x150) address=0xffff8880048083a8 value=0x8200080 rm-113 [005] ..Zff 10.000971: watch: (path_lookupat+0x97/0x1e0) address=0xffff8880048083a8 value=0x8200080 rm-113 [005] ..Zff 10.000984: watch: (lookup_fast+0xaa/0x150) address=0xffff8880048083a8 value=0x8200080 rm-113 [005] ..Zff 10.000988: watch: (path_lookupat+0x97/0x1e0) address=0xffff8880048083a8 value=0x8200080 rm-113 [005] ..Zff 10.001010: watch: (lookup_one_qstr_excl+0x28/0x140) address=0xffff8880048083a8 value=0x8200080 rm-113 [005] ..Zff 10.001014: watch: (lookup_one_qstr_excl+0xd1/0x140) address=0xffff8880048083a8 value=0x8200080 rm-113 [005] ..Zff 10.001018: watch: (may_delete_dentry+0x1c/0x200) address=0xffff8880048083a8 value=0x8200080 rm-113 [005] ..Zff 10.001021: watch: (may_delete_dentry+0x195/0x200) address=0xffff8880048083a8 value=0x8200080 rm-113 [005] ..Zff 10.001031: watch: (vfs_unlink+0x5e/0x260) address=0xffff8880048083a8 value=0x8200080 rm-113 [005] d.Z.. 10.001067: watch: (d_make_discardable+0x1b/0x40) address=0xffff8880048083a8 value=0x8200080 rm-113 [005] d.Z.. 10.001071: watch: (d_make_discardable+0x29/0x40) address=0xffff8880048083a8 value=0x200080 rm-113 [005] ...1. 10.001072: dentry_kill: (dentry_kill+0x0/0x2c0) dentry=0xffff8880048083a8 rm-113 [005] ...1. 10.001218: dentry_kill: (dentry_kill+0x0/0x2c0) dentry=0xffff8880048083a8 sh-107 [004] ...1. 10.001416: dentry_kill: (dentry_kill+0x0/0x2c0) dentry=0xffff8880049db110 sh-107 [004] ...1. 10.001444: dentry_kill: (dentry_kill+0x0/0x2c0) dentry=0xffff8880049db248 sh-107 [004] ...1. 10.001500: dentry_kill: (dentry_kill+0x0/0x2c0) dentry=0xffff888004ad6618 sh-107 [004] ...1. 10.002067: dentry_kill: (dentry_kill+0x0/0x2c0) dentry=0xffff888004b41e78 sh-107 [004] ...1. 10.904920: dentry_kill: (dentry_kill+0x0/0x2c0) dentry=0xffff888004b41e78 sh-107 [004] ...1. 10.905129: dentry_kill: (dentry_kill+0x0/0x2c0) dentry=0xffff888004ad6618 Thank you, --- Jinchao Wang (2): x86/hw_breakpoints: Make DR7 updates NMI safe x86/hw_breakpoints: Add arch_modify_local_hw_breakpoint_addr() API Masami Hiramatsu (Google) (9): HWBP: Add modify_local_hw_breakpoint_addr() API tracing: wprobe: Add watchpoint probe event based on hardware breakpoint x86: hw_breakpoint: Add a kconfig to clarify when a breakpoint fires selftests: tracing: Add a basic testcase for wprobe selftests: tracing: Add syntax testcase for wprobe tracing: wprobe: Add wprobe event trigger selftests: ftrace: Add wprobe trigger testcase tracing/wprobe: Support BTF typecast in fetchargs tracing/wprobe: Support BTF typecast in wprobe trigger command Documentation/trace/index.rst | 1 Documentation/trace/wprobetrace.rst | 163 ++ arch/Kconfig | 18 arch/x86/Kconfig | 2 arch/x86/include/asm/debugreg.h | 36 - arch/x86/include/asm/hw_breakpoint.h | 2 arch/x86/kernel/cpu/mce/core.c | 20 arch/x86/kernel/hw_breakpoint.c | 125 +- arch/x86/kernel/nmi.c | 10 arch/x86/kernel/traps.c | 10 include/linux/hw_breakpoint.h | 6 include/linux/trace_events.h | 3 kernel/events/hw_breakpoint.c | 35 + kernel/trace/Kconfig | 24 kernel/trace/Makefile | 1 kernel/trace/trace.c | 9 kernel/trace/trace.h | 6 kernel/trace/trace_events_trigger.c | 2 kernel/trace/trace_probe.c | 34 kernel/trace/trace_probe.h | 15 kernel/trace/trace_wprobe.c | 1392 ++++++++++++++++++++ tools/testing/selftests/ftrace/config | 3 .../ftrace/test.d/dynevent/add_remove_wprobe.tc | 63 + .../test.d/dynevent/wprobes_syntax_errors.tc | 21 .../test.d/trigger/trigger-wprobe-btf-offset.tc | 74 + .../test.d/trigger/trigger-wprobe-btf-typecast.tc | 72 + .../ftrace/test.d/trigger/trigger-wprobe.tc | 85 + 27 files changed, 2156 insertions(+), 76 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 create mode 100644 tools/testing/selftests/ftrace/test.d/trigger/trigger-wprobe-btf-offset.tc create mode 100644 tools/testing/selftests/ftrace/test.d/trigger/trigger-wprobe-btf-typecast.tc create mode 100644 tools/testing/selftests/ftrace/test.d/trigger/trigger-wprobe.tc -- Masami Hiramatsu (Google) [off-list ref]