linux-kernel - Re: [PATCH v3 11/19] unwind: Add deferred user space unwinding API

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: <20241030140324.GM14555@noisy.programming.kicks-ass.net>
Date: Wed, 30 Oct 2024 15:03:24 +0100
From: Peter Zijlstra <peterz@...radead.org>
To: Steven Rostedt <rostedt@...dmis.org>
Cc: Mathieu Desnoyers <mathieu.desnoyers@...icios.com>,
	Josh Poimboeuf <jpoimboe@...nel.org>, x86@...nel.org,
	Ingo Molnar <mingo@...nel.org>,
	Arnaldo Carvalho de Melo <acme@...nel.org>,
	linux-kernel@...r.kernel.org, Indu Bhagat <indu.bhagat@...cle.com>,
	Mark Rutland <mark.rutland@....com>,
	Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
	Jiri Olsa <jolsa@...nel.org>, Namhyung Kim <namhyung@...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, Jordan Rome <jordalgo@...a.com>,
	Sam James <sam@...too.org>, linux-trace-kernel@...r.kerne.org,
	Andrii Nakryiko <andrii.nakryiko@...il.com>,
	Jens Remus <jremus@...ux.ibm.com>,
	Florian Weimer <fweimer@...hat.com>,
	Andy Lutomirski <luto@...nel.org>
Subject: Re: [PATCH v3 11/19] unwind: Add deferred user space unwinding API

On Wed, Oct 30, 2024 at 02:17:22AM -0400, Steven Rostedt wrote:
> On Tue, 29 Oct 2024 19:20:32 +0100
> Peter Zijlstra <peterz@...radead.org> wrote:
> 
> > The 48:16 bit split gives you uniqueness for around 78 hours at 1GHz.
> 
> Are you saying that there will be one system call per nanosecond? This
> number is incremented only when a task enters the kernel from user
> spaces *and* requests a stack trace. If that happens 1000 times a
> second, that would still be around 9000 years.

We used to be able to do well over a million syscalls a second. I'm not
exactly sure where we are now, the whole speculation shit-show hurt
things quite badly.

> > 
> > But seriously, perf doesn't need this. It really only needs a sequence
> > number if you care to stitch over a LOST packet (and I can't say I care
> > about that case much) -- and doing that right doesn't really take much
> > at all.
> 
> Perf may not care because it has a unique descriptor per task, right?
> Where it can already know what events are associated to a task. But
> that's just a unique characteristic of perf. The unwinder should give a
> identifier for every user space stack trace that it will produce and
> pass that back to the tracer when it requests a stack trace but it
> cannot yet be performed. This identifier is what we are calling a
> context cookie. Then when it wants the stack trace, the unwinder will
> give the tracer the stack trace along with the identifier
> (context-cookie) that this stack trace was for in the past.

You're designing things inside out again. You should add functionality
by adding layers.

Pass a void * into the 'request-unwind' and have the 'do-unwind'
callback get that same pointer. Then anybody that needs identifiers to
figure out where things came from can stuff something in there.