linux-kernel - Re: [PATCH -next v1 0/3] kernel/events/uprobes: uprobe_write

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Message-ID: <CAEf4BzZcc6D3u5ATQmpkBt=8EhNuG7Xaibywx=hXcXTp346uFA@mail.gmail.com>
Date: Wed, 5 Mar 2025 11:58:46 -0800
From: Andrii Nakryiko <andrii.nakryiko@...il.com>
To: David Hildenbrand <david@...hat.com>
Cc: Oleg Nesterov <oleg@...hat.com>, Andrii Nakryiko <andrii@...nel.org>, Jiri Olsa <jolsa@...nel.org>, 
	linux-kernel@...r.kernel.org, linux-mm@...ck.org, 
	linux-arm-kernel@...ts.infradead.org, linux-trace-kernel@...r.kernel.org, 
	linux-perf-users@...r.kernel.org, Andrew Morton <akpm@...ux-foundation.org>, 
	Matthew Wilcox <willy@...radead.org>, Russell King <linux@...linux.org.uk>, 
	Masami Hiramatsu <mhiramat@...nel.org>, Peter Zijlstra <peterz@...radead.org>, 
	Ingo Molnar <mingo@...hat.com>, Arnaldo Carvalho de Melo <acme@...nel.org>, Namhyung Kim <namhyung@...nel.org>, 
	Mark Rutland <mark.rutland@....com>, 
	Alexander Shishkin <alexander.shishkin@...ux.intel.com>, Ian Rogers <irogers@...gle.com>, 
	Adrian Hunter <adrian.hunter@...el.com>, "Liang, Kan" <kan.liang@...ux.intel.com>, 
	Tong Tiangen <tongtiangen@...wei.com>
Subject: Re: [PATCH -next v1 0/3] kernel/events/uprobes: uprobe_write_opcode() rewrite

On Wed, Mar 5, 2025 at 11:47 AM David Hildenbrand <david@...hat.com> wrote:
>
> On 05.03.25 20:43, Andrii Nakryiko wrote:
> > On Wed, Mar 5, 2025 at 7:22 AM Oleg Nesterov <oleg@...hat.com> wrote:
> >>
> >> On 03/04, David Hildenbrand wrote:
> >>>
> >>> Currently, uprobe_write_opcode() implements COW-breaking manually, which is
> >>> really far from ideal.
> >>
> >> To say at least ;)
> >>
> >> David, thanks for doing this. I'll try to read 3/3 tomorrow, but I don't
> >> think I can really help. Let me repeat, this code was written many years
> >> ago, I forgot everything, and today my understanding of mm/ is very poor.
> >> But I'll try anyway.
> >>
> >>> Are there any uprobe tests / benchmarks that are worth running?
> >>
> >> All I know about uprobe tests is that bpf people run a lot of tests which
> >> use uprobes.
> >>
> >> Andrii, Jiri, what you advise?
> >>
> >
> > We do have a bunch of tests within BPF selftests:
> >
> > cd tools/testing/selftest/bpf && make -j$(nproc) && sudo ./test_progs -t uprobe
>
> I stumbled over them, but was so far not successful in building them in
> my test VM (did not try too hard, though). Will try harder now that I
> know that it actually tests uprobe properly :)

If you have decently recent Clang and pahole, then just make sure you
have kernel built before you build selftests. So above instructions
are more like:

1. cd <linux-repo>
2. cat tools/testing/selftests/bpf/{config, config.<your_arch>} >> .config
3. make -j$(nproc) # build kernel with that adjusted config
4. cd tools/testing/selftests/bpf
5. make -j$(nproc) # build BPF selftests
6. sudo ./test_progs -t uprobe # run selftests with "uprobe" in their name

>
> >
> > I also built an uprobe-stress tool to validate uprobe optimizations I
> > was doing, this one is the most stand-alone thing to use for testing,
> > please consider checking that. You can find it at [0], and see also
> > [1] and [2] where  I was helping Peter to build it from sources, so
> > that might be useful for you as well, if you run into problems with
> > building. Running something like `sudo ./uprobe-stress -a10 -t5 -m5
> > -f3` would hammer on this quite a bit.
>
> Thanks, I'll play with that as well.
>
> >
> > I'm just about to leave on a short vacation, so won't have time to go
> > over patches, but I plan to look at them when I'm back next week.
> >
> >    [0] https://github.com/libbpf/libbpf-bootstrap/tree/uprobe-stress
> >    [1] https://lore.kernel.org/linux-trace-kernel/CAEf4BzZ+ygwfk8FKn5AS_Ny=igvGcFzdDLE2FjcvwjCKazEWMA@mail.gmail.com/
> >    [2] https://lore.kernel.org/linux-trace-kernel/CAEf4BzZqKCR-EQz6LTi-YvFY4RnYb_NnQXtwgZCv6aUo7gjkHg@mail.gmail.com
> >
> >> Oleg.
> >>
> >
>
>
> --
> Cheers,
>
> David / dhildenb
>