Re: [Bug 209317] ftrace kernel self test failure on RISC-V on 5.8, regression from 5.4.0

From: Atish Patra <atishp@atishpatra.org>
To: Zong Li <zong.li@sifive.com>
Cc: "aou@eecs.berkeley.edu" <aou@eecs.berkeley.edu>,
	Alan Kao <alankao@andestech.com>,
	"bugzilla-daemon@bugzilla.kernel.org"
	<bugzilla-daemon@bugzilla.kernel.org>,
	"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
	"rostedt@goodmis.org" <rostedt@goodmis.org>,
	Atish Patra <Atish.Patra@wdc.com>,
	"palmer@dabbelt.com" <palmer@dabbelt.com>,
	"paul.walmsley@sifive.com" <paul.walmsley@sifive.com>,
	"linux-riscv@lists.infradead.org"
	<linux-riscv@lists.infradead.org>
Subject: Re: [Bug 209317] ftrace kernel self test failure on RISC-V on 5.8, regression from 5.4.0
Date: Mon, 5 Oct 2020 11:47:07 -0700	[thread overview]
Message-ID: <CAOnJCULU7qy35vhiFcJKHFgbe+w5Gn2q_SskjjbjtM3X90uT_g@mail.gmail.com> (raw)
In-Reply-To: <CANXhq0qzi2LjYekG0yk876znrpk7tMo+-zT6wR77nhy89rm2kQ@mail.gmail.com>

On Sun, Oct 4, 2020 at 11:08 PM Zong Li <zong.li@sifive.com> wrote:
>
> Hi Atish,
>
> I can take out some time to take a look at it together, if anyone here
> fixes it or has ideas, please share the information, thanks.
>

Thanks. I observed this in case it helps.

Across kernels, the panic trace seems to point out the one of the
first two functions after patching is corrupted.
rcu_momentary_dyntick_idle or stop_machine_yield[1]

[1]https://elixir.bootlin.com/linux/v5.9-rc7/source/kernel/stop_machine.c#L213

I am suspecting nop was not replaced with the correct auipc+jalr pair?

> On Sun, Oct 4, 2020 at 1:33 AM Atish Patra <atishp@atishpatra.org> wrote:
> >
> > Hi Alan and Zong,
> > I initially suspected ftrace is broken between v5.6 & v5.7 as Kolin pointed out.
> > I couldn't find any reason how the HSM patch is related. Zong's ftrace
> > patching code was also merged in that release.
> > However, I was able to reproduce the issue in the older kernel(v5.4)
> > as well on both Qemu & Unleashed hardware.
> > Here are the steps:
> >
> > mount -t debugfs none /sys/kernel/debug/
> > cd /sys/kernel/debug/tracing
> > echo function_graph > current_tracer
> > echo function > current_tracer
> >
> > It works for the first time with function_graph but writing any other
> > tracer crashes immediately.
> > Can you take a look to check if the bug is in ftrace infrastructure code ?
> >
> > On Mon, Sep 28, 2020 at 10:25 AM Atish Patra <Atish.Patra@wdc.com> wrote:
> > >
> > > On Mon, 2020-09-28 at 11:13 -0400, Steven Rostedt wrote:
> > > > On Sat, 26 Sep 2020 22:02:35 +0000
> > > > bugzilla-daemon@bugzilla.kernel.org wrote:
> > > >
> > > > > https://bugzilla.kernel.org/show_bug.cgi?id=209317
> > > > >
> > > > > --- Comment #4 from Colin Ian King (colin.king@canonical.com) ---
> > > > > Issue still in 5.9-rc6
> > > > >
> > > >
> > > > Atish,
> > > >
> > > > As the issues bisects down to your commit, care to take a look at
> > > > this.
> > > > (And take ownership of this bug)
> > > >
> > >
> > > Yes. I am already looking into this. Colin informed me about the bug
> > > over the weekend.
> > >
> > > I couldn't change the ownership as I am not part of the editbugs group.
> > > I have sent an email to helpdesk@kernel.org for access.
> > >
> > > > -- Steve
> > >
> > > --
> > > Regards,
> > > Atish
> > > _______________________________________________
> > > linux-riscv mailing list
> > > linux-riscv@lists.infradead.org
> > > http://lists.infradead.org/mailman/listinfo/linux-riscv
> >
> >
> >
> > --
> > Regards,
> > Atish

-- 
Regards,
Atish

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