linux-kernel - Re: [PATCH] riscv: ftrace: no need to acquire text_mutex when executed in stop

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Message-ID: <20220310092742.4fcc7131@gandalf.local.home>
Date:   Thu, 10 Mar 2022 09:27:42 -0500
From:   Steven Rostedt <rostedt@...dmis.org>
To:     Changbin Du <changbin.du@...il.com>
Cc:     Paul Walmsley <paul.walmsley@...ive.com>,
        Ingo Molnar <mingo@...hat.com>,
        Albert Ou <aou@...s.berkeley.edu>,
        Palmer Dabbelt <palmer@...belt.com>,
        linux-riscv@...ts.infradead.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] riscv: ftrace: no need to acquire text_mutex when
 executed in stop_machine

On Thu, 10 Mar 2022 12:54:54 +0800
Changbin Du <changbin.du@...il.com> wrote:

> It's safe to patch text segment in stop_machine. No race is possible here.
> Besides, there is a false positive for the lock assertion in
> patch_insn_write() since the lock is not held by cpu migration thread.
> 
> So we actually don't need our ftrace_arch_code_modify_prepare/post(). And
> the lock assertion in patch_insn_write() should be removed to avoid
> producing lots of false positive warnings.
> 
> Signed-off-by: Changbin Du <changbin.du@...il.com>

Ideally, RISC-V should try to get off of the stop_machine approach, and
move to the breakpoint modification.

-- Steve