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From:   Atish Patra <atishp@atishpatra.org>
Date:   Tue, 3 Nov 2020 07:33:37 -0800
Message-ID: <CAOnJCU+kMJCrwJ5MD2pYRoub1TpVGgpfX=6nNG2uFB6PNJLEiA@mail.gmail.com>
Subject: Re: [PATCH] stop_machine: Mark functions as notrace
To:     Guo Ren <guoren@kernel.org>
Cc:     Steven Rostedt <rostedt@goodmis.org>, Zong Li <zong.li@sifive.com>,
        Paul McKenney <paulmck@kernel.org>, josh@joshtriplett.org,
        mathieu.desnoyers@efficios.com, jiangshanlai@gmail.com,
        joel@joelfernandes.org, vincent.whitchurch@axis.com,
        Thomas Gleixner <tglx@linutronix.de>,
        Paul Walmsley <paul.walmsley@sifive.com>,
        Palmer Dabbelt <palmerdabbelt@google.com>,
        Masami Hiramatsu <mhiramat@kernel.org>,
        Greentime Hu <greentime.hu@sifive.com>,
        Colin Ian King <colin.king@canonical.com>,
        rcu@vger.kernel.org,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
        linux-riscv <linux-riscv@lists.infradead.org>
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On Sat, Oct 31, 2020 at 12:42 AM Guo Ren <guoren@kernel.org> wrote:
>
> On Sat, Oct 31, 2020 at 8:28 AM Steven Rostedt <rostedt@goodmis.org> wrote:
> >
> > On Fri, 30 Oct 2020 14:47:56 -0700
> > Atish Patra <atishp@atishpatra.org> wrote:
> >
> > > > Look at arm64, they __kprobes flag and I guess it would also prevent
> > > > ftrace call site.
> > > >
> > >
> > > Are you sure about that ? __kprobes puts the code in .kprobes.text section
> > > which is under whitelist sections in recordmcount.pl & recordmcount.c.
> >
> > Correct, ftrace can trace functions marked with __kprobes. That said,
> I guess wrong, thx for correct me.
>
> > the instruction you are looking at here, is in a file that is
> > blacklisted from recordmcount.
> >
> >   CFLAGS_REMOVE_insn.o = $(CC_FLAGS_FTRACE)
> >
> > All ftrace flags are removed from the compiling of insn.c, and every
> > function in that file will not be traced.
> Yes, arm64 prevents the whole file from ftrace. My patch just use
> notrace flag setting on some functions.
>
> @Atish How do think:
> CFLAGS_REMOVE_cacheflush.o = $(CC_FLAGS_FTRACE)
> CFLAGS_REMOVE_sbi.o = $(CC_FLAGS_FTRACE)
>

Looks good to me. What should be done for copy_to_kernel_nofault ?
That is also in the calling path.

> --
> Best Regards
>  Guo Ren
>
> ML: https://lore.kernel.org/linux-csky/


-- 
Regards,
Atish