linux-kernel - Re: Why do kprobes and uprobes singlestep?

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Date:   Tue, 2 Mar 2021 17:22:30 -0800
From:   Alexei Starovoitov <alexei.starovoitov@...il.com>
To:     Andy Lutomirski <luto@...capital.net>
Cc:     Andy Lutomirski <luto@...nel.org>, bpf <bpf@...r.kernel.org>,
        Oleg Nesterov <oleg@...hat.com>,
        Masami Hiramatsu <mhiramat@...nel.org>,
        Peter Zijlstra <peterz@...radead.org>,
        LKML <linux-kernel@...r.kernel.org>,
        Anil S Keshavamurthy <anil.s.keshavamurthy@...el.com>,
        "David S. Miller" <davem@...emloft.net>, X86 ML <x86@...nel.org>,
        Andrew Cooper <andrew.cooper3@...rix.com>
Subject: Re: Why do kprobes and uprobes singlestep?

On Tue, Mar 2, 2021 at 1:02 PM Andy Lutomirski <luto@...capital.net> wrote:
>
>
> > On Mar 2, 2021, at 12:24 PM, Alexei Starovoitov <alexei.starovoitov@...il.com> wrote:
> >
> > On Tue, Mar 2, 2021 at 10:38 AM Andy Lutomirski <luto@...nel.org> wrote:
> >>
> >> Is there something like a uprobe test suite?  How maintained /
> >> actively used is uprobe?
> >
> > uprobe+bpf is heavily used in production.
> > selftests/bpf has only one test for it though.
> >
> > Why are you asking?
>
> Because the integration with the x86 entry code is a mess, and I want to know whether to mark it BROKEN or how to make sure the any cleanups actually work.

Any test case to repro the issue you found?
Is it a bug or just messy code?
Nowadays a good chunk of popular applications (python, mysql, etc) has
USDTs in them.
Issues reported with bcc:
https://github.com/iovisor/bcc/issues?q=is%3Aissue+USDT
Similar thing with bpftrace.
Both standard USDT and semaphore based are used in the wild.
uprobe for containers has been a long standing feature request.
If you can improve uprobe performance that would be awesome.
That's another thing that people report often. We optimized it a bit.
More can be done.