Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 2620:137:e000::1:20 as permitted sender) client-ip=2620:137:e000::1:20;
Date:   Sun, 13 Mar 2022 16:07:11 +0800
From:   Changbin Du <changbin.du@gmail.com>
To:     Steven Rostedt <rostedt@goodmis.org>
Cc:     Changbin Du <changbin.du@gmail.com>,
        Paul Walmsley <paul.walmsley@sifive.com>,
        Ingo Molnar <mingo@redhat.com>,
        Albert Ou <aou@eecs.berkeley.edu>,
        Palmer Dabbelt <palmer@dabbelt.com>,
        linux-riscv@lists.infradead.org, linux-kernel@vger.kernel.org
Subject: Re: [PATCH] riscv: ftrace: no need to acquire text_mutex when
 executed in stop_machine
Message-ID: <20220313080711.mrzsgtxpbycug2vm@mail.google.com>
References: <20220310045454.672097-1-changbin.du@gmail.com>
 <20220310092742.4fcc7131@gandalf.local.home>
MIME-Version: 1.0
Content-Type: text/plain; charset=us-ascii
Content-Disposition: inline
In-Reply-To: <20220310092742.4fcc7131@gandalf.local.home>
Precedence: bulk

On Thu, Mar 10, 2022 at 09:27:42AM -0500, Steven Rostedt wrote:
> On Thu, 10 Mar 2022 12:54:54 +0800
> Changbin Du <changbin.du@gmail.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@gmail.com>
> 
> Ideally, RISC-V should try to get off of the stop_machine approach, and
> move to the breakpoint modification.
>
yes, that's a further step. I can feel a obvious stall to enable ftrace running
in QEMU. (maybe qemu-riscv tcg is too slow...)

> -- Steve

-- 
Cheers,
Changbin Du