Hi Randy, On Sun, 14 Sep 2025 17:25:19 -0700 Randy Dunlap <rdun...@infradead.org> wrote:
> > > On 9/14/25 7:10 AM, Masami Hiramatsu (Google) wrote: > > From: Masami Hiramatsu (Google) <mhira...@kernel.org> > > > > Add wprobe event trigger to set and clear the watch event dynamically. > > This allows us to set an watchpoint on a given local variables and > > a slab object instead of static objects. > > > > The trigger syntax is below; > > below: > (just a nit :) OK. > > > > > - set_wprobe:WPROBE:FIELD[+OFFSET] [if FILTER] > > - clear_wprobe:WPROBE[:FIELD[+OFFSET]] [if FILTER] > > > > set_wprobe sets the address pointed by FIELD[+offset] to the WPROBE > > event. The FIELD is the field name of trigger event. > > clear_wprobe clears the watch address of WPROBE event. If the FIELD > > option is specified, it clears only if the current watch address is > > same as the given FIELD[+OFFSET] value. > > > > The set_wprobe trigger do not change type and length. That should be > > does should be done > ? OK. > > > set when a new wprobe is created. > > > > Also, the WPROBE event must be disabled when setting the new trigger > > and it will be busy afterwards. Recommended usage is to add a new > > wprobe at NULL address and keep disabled. > > > > Signed-off-by: Masami Hiramatsu (Google) <mhira...@kernel.org> > > --- > > Changes in v3: > > - Add FIELD option support for clear_wprobe and update document. > > - Fix to unregister/free event_trigger_data on file correctly. > > - Fix syntax comments. > > Changes in v2: > > - Getting local cpu perf_event from trace_wprobe directly. > > - Remove trace_wprobe_local_perf() because it is conditionally unused. > > - Make CONFIG_WPROBE_TRIGGERS a hidden config. > > --- > > Documentation/trace/wprobetrace.rst | 88 +++++++ > > include/linux/trace_events.h | 1 > > kernel/trace/Kconfig | 10 + > > kernel/trace/trace_wprobe.c | 430 > > +++++++++++++++++++++++++++++++++++ > > 4 files changed, 529 insertions(+) > > > > diff --git a/Documentation/trace/wprobetrace.rst > > b/Documentation/trace/wprobetrace.rst > > index 9774f57e2947..a1812a8ac491 100644 > > --- a/Documentation/trace/wprobetrace.rst > > +++ b/Documentation/trace/wprobetrace.rst > > @@ -67,3 +67,91 @@ Here is an example to add a wprobe event on a variable > > `jiffies`. > > <idle>-0 [000] d.Z1. 717.026373: my_jiffies: > > (tick_do_update_jiffies64+0xbe/0x130) > > > > You can see the code which writes to `jiffies` is `do_timer()`. > > + > > +Combination with trigger action > > +------------------------------- > > +The event trigger action can extend the utilization of this wprobe. > > + > > +- set_wprobe:WPEVENT:FIELD[+|-ADJUST] > > +- clear_wprobe:WPEVENT[:FIELD[+|-]ADJUST] > > + > > +Set these triggers to the target event, then the WPROBE event will be > > +setup to trace the memory access at FIELD[+|-ADJUST] address. > > +When clear_wprobe is hit, if FIELD is NOT specified, the WPEVENT is > > +forcibly cleared. If FIELD[[+|-]ADJUST] is set, it clears WPEVENT only > > +if its watching address is the same as the FIELD[[+|-]ADJUST] value. > > + > > +Notes: > > +The set_wprobe trigger do not change type and length. That should be > does not should be done OK. > > > > +set when a new wprobe is created. > > + > > +The WPROBE event must be disabled when setting the new trigger > > +and it will be busy afterwards. Recommended usage is to add a new > > +wprobe at NULL address and keep disabled. > > + > > + > > +For example, trace the first 8 byte of the dentry data structure passed > > bytes OK > > > +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 > > Just using '>' here is OK? Yes, until this, no probe hooks do_truncate, so it should not kick any events. But maybe it is better to use '>>' to avoid confusing. > > > + > > + # 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; > > Usually that should be: show: > > but in .rst it might need to be show:: Ah,, yes, that's right. I missed that. Thank you! > > I don't know. Haven't tested it. > > > -- > ~Randy > -- Masami Hiramatsu (Google) <mhira...@kernel.org>
