linux-kernel - Re: [RFC][PATCH] kprobes: Remove kprobe::fault

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Date:   Wed, 10 Feb 2021 11:47:43 -0800
From:   Alexei Starovoitov <alexei.starovoitov@...il.com>
To:     Peter Zijlstra <peterz@...radead.org>
Cc:     Andy Lutomirski <luto@...nel.org>, X86 ML <x86@...nel.org>,
        LKML <linux-kernel@...r.kernel.org>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        Yonghong Song <yhs@...com>,
        Masami Hiramatsu <mhiramat@...nel.org>
Subject: Re: [RFC][PATCH] kprobes: Remove kprobe::fault_handler

On Wed, Feb 10, 2021 at 5:57 AM Peter Zijlstra <peterz@...radead.org> wrote:
>
>
> Somewhat related.. I had this pending.
>
> ---
> Subject: kprobes: Remove kprobe::fault_handler
> From: Peter Zijlstra <peterz@...radead.org>
> Date: Tue Feb 2 10:43:41 CET 2021
>
> The reason for kprobe::fault_handler(), as given by their comment:
>
>  * We come here because instructions in the pre/post
>  * handler caused the page_fault, this could happen
>  * if handler tries to access user space by
>  * copy_from_user(), get_user() etc. Let the
>  * user-specified handler try to fix it first.
>
> If just plain bad. Those other handlers are ran from non-preemptible
> context and had better use _nofault() functions. Also, there is no
> upstream usage of this.

No objections from me.

Since Masami mentioned that systemtap used that you
probably want to give them a courtesy heads-up that it's going away.
Though looking at systemtap source code I couldn't find any
reference to it. So it's likely a nop for them anyway.