linux-kernel - Re: [PATCH RFC 04/10] perf: Introduce deferred user callchains

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <CAM9d7chg8c4yftXgAyZZyLuYJQaWYDTa9YY5x-S+Mb-8SM8K-A@mail.gmail.com>
Date:   Mon, 13 Nov 2023 09:48:32 -0800
From:   Namhyung Kim <namhyung@...nel.org>
To:     Peter Zijlstra <peterz@...radead.org>
Cc:     Josh Poimboeuf <jpoimboe@...nel.org>,
        Steven Rostedt <rostedt@...dmis.org>,
        Ingo Molnar <mingo@...nel.org>,
        Arnaldo Carvalho de Melo <acme@...nel.org>,
        linux-kernel@...r.kernel.org, x86@...nel.org,
        Indu Bhagat <indu.bhagat@...cle.com>,
        Mark Rutland <mark.rutland@....com>,
        Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
        Jiri Olsa <jolsa@...nel.org>, Ian Rogers <irogers@...gle.com>,
        Adrian Hunter <adrian.hunter@...el.com>,
        linux-perf-users@...r.kernel.org, Mark Brown <broonie@...nel.org>,
        linux-toolchains@...r.kernel.org
Subject: Re: [PATCH RFC 04/10] perf: Introduce deferred user callchains

On Mon, Nov 13, 2023 at 9:21 AM Peter Zijlstra <peterz@...radead.org> wrote:
>
> On Mon, Nov 13, 2023 at 08:56:39AM -0800, Namhyung Kim wrote:
>
> > Ok, then BPF gets no user call stacks even with sframes.
>
> Well, you could obviously run another BPF program at return to user and
> stitch there.

Right, maybe some more work needed for bpf_get_stackid()
but it seems possible.

>
> > Ok, but ...
>
> > If the task is preempted, the call stack would be from another
> > task (if it also has the pending call stacks) and we need to
> > check which user call stack matches which kernel call stack.
> > So there's no guarantee we can just use adjacent samples.
>
> So upon requesting a user backtrace for the task it could request a
> token (from eg a global atomic u64 in the most crude case) and place
> this in the task_struct. The backtrace will emit this as forward
> reference for the user trace.
>
> Once the task_work generates the user stacktrace, it will again dump
> this token along with the user unwind, after which it will reset the
> token for this this task (to 0).

Yeah, I thought something like this first, but then I thought
"can we just use PID for this?"

Thanks,
Namhyung