[PATCH v15 00/12] tracing: wprobe: x86: Add wprobe for watchpoint
From: "Masami Hiramatsu (Google)" <mhiramat@kernel.org>
Date: 2026-09-07 03:46:24
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Hi, Here is the 15th 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/178810001186.64882.2161016469449127450.stgit@devnote2/ (local) In this version, previous bugfix patches for BTF kflag resolution and RCU-protected kprobe blacklist were sent to Linus via probe/fixes, reducing the series to 12 patches. This version addresses feedbacks from Sashiko on v14[1], and more local fixes such as x86 debug register manipulation, validates watched address and natural alignment, tracks missed events on SMP update failures(*), prevents in-place command string modification during trigger parsing, adds explicit failure checks in selftests, and documents BTF typecast and struct offset syntax. I also added Assited-by: tags for this update. [1] https://sashiko.dev/#/patchset/178810001186.64882.2161016469449127450.stgit%40devnote2 (*) currently it just increase a missed counter. Detailed changes are here. Changes in v15: - x86/mce: Move local_db_save() to entry of exc_machine_check_kernel() and restore it on early return from mce_check_crashing_cpu() to prevent nested #DB on watched variables. - x86/hw_breakpoints: Always preserve DR7_FIXED_1 in arch_install_hw_breakpoint(), arch_uninstall_hw_breakpoint(), and hw_breakpoint_restore() for architectural compliance. - x86/hw_breakpoints: Wrap local_db_save() in a cpu_dr7_seq loop to detect NMI breakpoint updates and ensure DR7 is disabled before entry. - x86/hw_breakpoints: In local_db_restore(), restore DR7_FIXED_1 if saved dr7 is 0 and an NMI updated breakpoints, preserving KVM guest isolation. - x86/hw_breakpoints: Always write "val | DR7_FIXED_1" to hardware DR7 in local_db_restore() for architectural compliance. - x86/hw_breakpoints: Avoid modifying saved dr7 in-place across retry loops. - x86/hw_breakpoints: Temporarily clear breakpoint enable bit in DR7 before updating debug address register and re-enable it afterward to comply with x86 specification and avoid spurious #DBs. - HWBP: Annotate counter_arch_bp(bp)->address and bp->attr.bp_addr with WRITE_ONCE() in both update and rollback paths to prevent data races with concurrent readers (e.g. NMI handlers). - tracing/wprobe: Introduce trace_wprobe_is_valid_addr() to validate target address and natural alignment for wprobe length during event creation and trigger setup. - tracing/wprobe: Initialize irq_work and work immediately after allocation in alloc_trace_wprobe() and check tw->work.func in free_trace_wprobe() to prevent WARN_ON(!work->func) on early failures. - tracing/wprobe: Record SMP local update failures in tw->missed counter and expose missed event count as a trailing comment in trigger file. - tracing/wprobe: Duplicate field string in wprobe_trigger_typecast_parse() to avoid modifying glob in place so tracing_log_err() logs the pristine command string. - tracing/wprobe: Remove leftover offset and adjust debug print in wprobe_trigger_print(). - tracing/wprobe: Add set_wprobe and clear_wprobe triggers to readme_msg in trace.c. - tracing/wprobe: Move variable declarations to function entry in trace_wprobe_show(), fix tab indentation in trace.c, and wrap lines exceeding 100 columns. - Documentation: Document BTF typecast in fetchargs and BTF struct offset resolution in set_wprobe trigger in wprobetrace.rst. - selftests/ftrace: Add explicit failure checks with fail helper across trigger-wprobe.tc, trigger-wprobe-btf-typecast.tc, and trigger-wprobe-btf-offset.tc. - selftests/ftrace: Declare fprobe README requirement in trigger tests and trigger file check in trigger-wprobe-syntax-errors.tc requires line. 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 linux-trace/probes/fixes. Usage ----- The basic usage of this wprobe is similar to other probes; w:[GRP/][EVENT] [r|w|rw]@<ADDRESS|SYMBOL[+|-OFFS]>[:LEN] [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($addr)' >> dynamic_events echo 1 > events/wprobes/my_jiffies/enable Moreover, this can be combined with event trigger to trace the memory access on slab objects. The trigger syntax is; set_wprobe:WPROBE_EVENT:FIELD[+|-OFFSET][:COUNT] [if FILTER] clear_wprobe:WPROBE_EVENT[:FIELD[+|-OFFSET][:COUNT]] [if FILTER] set_wprobe sets WPROBE_EVENT's watch address on FIELD[+|-OFFSET]. clear_wprobe clears WPROBE_EVENT's watch address if it is set to FIELD[+|-OFFSET]. If FIELD is omitted, forcibly clear the watch address when trigger event is hit. For example, trace the first 8 byte of the dentry data structure passed to do_truncate() until it is deleted by dentry_kill(). (Note: all tracefs setup uses '>>' so that it does not kick do_truncate()) # echo 'w:watch rw@-1:8 address=$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, --- base-commit: 0c4256196b3a105307e2235fbfd85e768bbcdd0f 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) (10): x86/mce: Fix hardware debug register corruption on task migration HWBP: Add modify_local_hw_breakpoint_addr() API tracing/wprobe: Add wprobe (watchpoint probe) trace event support 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 set_wprobe and clear_wprobe event triggers selftests: tracing: Add wprobe trigger testcase tracing/wprobe: Support BTF typecast in fetchargs tracing/wprobe: Support BTF struct offset resolution in set_wprobe trigger Documentation/trace/index.rst | 1 Documentation/trace/wprobetrace.rst | 200 +++ arch/Kconfig | 18 arch/x86/Kconfig | 2 arch/x86/include/asm/debugreg.h | 67 + arch/x86/include/asm/hw_breakpoint.h | 2 arch/x86/kernel/cpu/mce/core.c | 29 arch/x86/kernel/hw_breakpoint.c | 151 +- arch/x86/kernel/nmi.c | 7 arch/x86/kernel/traps.c | 10 include/linux/hw_breakpoint.h | 6 include/linux/trace_events.h | 3 kernel/events/hw_breakpoint.c | 48 + kernel/trace/Kconfig | 24 kernel/trace/Makefile | 1 kernel/trace/trace.c | 13 kernel/trace/trace.h | 6 kernel/trace/trace_events_trigger.c | 2 kernel/trace/trace_probe.c | 36 kernel/trace/trace_probe.h | 22 kernel/trace/trace_wprobe.c | 1522 ++++++++++++++++++++ tools/testing/selftests/ftrace/config | 3 .../ftrace/test.d/dynevent/add_remove_wprobe.tc | 63 + .../test.d/dynevent/wprobes_syntax_errors.tc | 23 .../test.d/trigger/trigger-wprobe-btf-offset.tc | 85 + .../test.d/trigger/trigger-wprobe-btf-typecast.tc | 85 + .../test.d/trigger/trigger-wprobe-syntax-errors.tc | 37 .../ftrace/test.d/trigger/trigger-wprobe.tc | 107 + 28 files changed, 2476 insertions(+), 97 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-syntax-errors.tc create mode 100644 tools/testing/selftests/ftrace/test.d/trigger/trigger-wprobe.tc -- Masami Hiramatsu (Google) [off-list ref]