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

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Date:   Sun, 13 Mar 2022 16:07:11 +0800
From:   Changbin Du <changbin.du@...il.com>
To:     Steven Rostedt <rostedt@...dmis.org>
Cc:     Changbin Du <changbin.du@...il.com>,
        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, Mar 10, 2022 at 09:27:42AM -0500, Steven Rostedt wrote:
> 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.
>
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