linux-kernel - Re: [PATCH v4 9/9] riscv: Fixup lockdep_assert_held(&text_mutex) in patch_insn

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Date:   Wed, 21 Oct 2020 16:27:02 +0800
From:   Guo Ren <guoren@...nel.org>
To:     Steven Rostedt <rostedt@...dmis.org>
Cc:     Atish Patra <atishp@...shpatra.org>, Zong Li <zong.li@...ive.com>,
        Palmer Dabbelt <palmerdabbelt@...gle.com>,
        Paul Walmsley <paul.walmsley@...ive.com>,
        Masami Hiramatsu <mhiramat@...nel.org>,
        Alan Kao <alankao@...estech.com>,
        Patrick Stählin <me@...ki.ch>,
        Guo Ren <guoren@...ux.alibaba.com>,
        Anup Patel <anup@...infault.org>,
        "linux-kernel@...r.kernel.org List" <linux-kernel@...r.kernel.org>,
        linux-csky@...r.kernel.org, Greentime Hu <greentime.hu@...ive.com>,
        linux-riscv <linux-riscv@...ts.infradead.org>
Subject: Re: [PATCH v4 9/9] riscv: Fixup lockdep_assert_held(&text_mutex) in patch_insn_write

Why?

funca:
nop                   addi  sp,sp, -8
nop                   sd ra, 0(sp)
nop, nop           auipc ra, 0x?
nop, nop  ->      jalr -?(ra)
nop                   ld ra,0(sp)
nop                   addi sp,sp, 8

When CPU0 has only changed half of them, CPU1 call funca then CPU1 broken.

On Wed, Oct 21, 2020 at 4:41 AM Steven Rostedt <rostedt@...dmis.org> wrote:
>
> On Tue, 20 Oct 2020 19:18:01 +0800
> Guo Ren <guoren@...nel.org> wrote:
>
> > > What platform are you testing ? We are seeing a crash while enabling
> > > any of the tracers multiple times
> > > on Qemu/HiFive Unleashed.
> > I use qemu for testing. I've changed dynamic ftrace mechanism from
> > mcount to -fpatchable-entry.
> >
> > The problem is made by the lockdep checking of text_mutex.
>
> If you are switching to "patchable-entry" you shouldn't need to use
> stop_machine for the updates. No?
>
> -- Steve



--
Best Regards
 Guo Ren

ML: https://lore.kernel.org/linux-csky/