linux-kernel - Re: [PATCH v2] perf,x86: avoid missing caller address in stack traces captured in uprobe

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Message-ID: <20240703061119.iamshulwf3qzsdu3@treble>
Date: Tue, 2 Jul 2024 23:11:19 -0700
From: Josh Poimboeuf <jpoimboe@...nel.org>
To: Andrii Nakryiko <andrii.nakryiko@...il.com>
Cc: Andrii Nakryiko <andrii@...nel.org>, linux-trace-kernel@...r.kernel.org,
	peterz@...radead.org, rostedt@...dmis.org, mhiramat@...nel.org,
	x86@...nel.org, mingo@...hat.com, tglx@...utronix.de,
	linux-kernel@...r.kernel.org, bpf@...r.kernel.org, rihams@...com,
	linux-perf-users@...r.kernel.org
Subject: Re: [PATCH v2] perf,x86: avoid missing caller address in stack
 traces captured in uprobe

On Tue, Jul 02, 2024 at 08:35:08PM -0700, Andrii Nakryiko wrote:
> On Tue, Jul 2, 2024 at 6:11 PM Josh Poimboeuf <jpoimboe@...nel.org> wrote:
> > On Tue, Jul 02, 2024 at 05:06:14PM -0700, Andrii Nakryiko wrote:
> > > In general, even with false positives, I think it's overwhelmingly
> > > better to get correct entry stack trace 99.9% of the time, and in the
> > > rest 0.01% cases it's fine having one extra bogus entry (but the rest
> > > should still be correct), which should be easy for humans to recognize
> > > and filter out, if necessary.
> >
> > Agreed, this is a definite improvement overall.
> 
> Cool, I'll incorporate that into v3 and send it soon.
> 
> >
> > BTW, soon there will be support for sframes instead of frame pointers,
> > at which point these checks should only be done for the frame pointer
> > case.
> 
> Nice, this is one of the reasons I've been thinking about asynchronous
> stack trace capture in BPF (see [0] from recent LSF/MM).
>  [0] https://docs.google.com/presentation/d/1k10-HtK7pP5CMMa86dDCdLW55fHOut4co3Zs5akk0t4

I don't seem to have permission to open it.

> Few questions, while we are at it. Does it mean that
> perf_callchain_user() will support working from sleepable context and
> will wait for data to be paged in? Is anyone already working on this?
> Any pointers?

I had a prototype here:

  https://lkml.kernel.org/lkml/cover.1699487758.git.jpoimboe@kernel.org

Hopefully I can get started on v2 soon.

-- 
Josh