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

Andrii Nakryiko
2024-07-03T20:23:52Z

On Tue, Jul 2, 2024 at 11:11 PM Josh Poimboeuf <jpoimboe@kernel.org> wrote:
>
> 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@kernel.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, if you have a chance, please do take a look at v3 and leave your
ack, if you are ok with it. Thanks!

> > >
> > > 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.
>

Argh, sorry, it's under my corporate account which doesn't allow
others to view it. Try this, I "published" it, let me know if that
still doesn't work:

[0] https://docs.google.com/presentation/d/e/2PACX-1vRgL3UPbkrznwtNPKn-sSjvan7tFeMqOrIyZAFSSEPYiWG20JGSP80jBmZqGwqMuBGVmv9vyLU4KRTx/pub

> > 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.

Ok, so you are going to work on this. Please cc me on future revisions
then. Thanks!

>
> --
> Josh