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From:   Marco Elver <elver@google.com>
Date:   Fri, 20 Nov 2020 20:22:01 +0100
Message-ID: <CANpmjNN+smYsdcJDDHNCT9aD_WULV3q6UmVRAutKPjzGVi_yfQ@mail.gmail.com>
Subject: Re: linux-next: stall warnings and deadlock on Arm64 (was: [PATCH]
 kfence: Avoid stalling...)
To:     Steven Rostedt <rostedt@goodmis.org>
Cc:     "Paul E. McKenney" <paulmck@kernel.org>,
        Anders Roxell <anders.roxell@linaro.org>,
        Andrew Morton <akpm@linux-foundation.org>,
        Alexander Potapenko <glider@google.com>,
        Dmitry Vyukov <dvyukov@google.com>,
        Jann Horn <jannh@google.com>,
        Mark Rutland <mark.rutland@arm.com>,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
        Linux-MM <linux-mm@kvack.org>,
        kasan-dev <kasan-dev@googlegroups.com>, rcu@vger.kernel.org,
        Peter Zijlstra <peterz@infradead.org>,
        Tejun Heo <tj@kernel.org>,
        Lai Jiangshan <jiangshanlai@gmail.com>,
        Linux ARM <linux-arm-kernel@lists.infradead.org>
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Precedence: bulk

On Fri, 20 Nov 2020 at 20:16, Steven Rostedt <rostedt@goodmis.org> wrote:
>
> On Fri, 20 Nov 2020 19:17:37 +0100
> Marco Elver <elver@google.com> wrote:
>
> > > > +++ b/kernel/rcu/Makefile
> > > > @@ -3,6 +3,13 @@
> > > >  # and is generally not a function of system call inputs.
> > > >  KCOV_INSTRUMENT := n
> > > >
> > > > +ifdef CONFIG_FUNCTION_TRACER
> > > > +CFLAGS_REMOVE_update.o = $(CC_FLAGS_FTRACE)
> > > > +CFLAGS_REMOVE_sync.o = $(CC_FLAGS_FTRACE)
> > > > +CFLAGS_REMOVE_srcutree.o = $(CC_FLAGS_FTRACE)
> > > > +CFLAGS_REMOVE_tree.o = $(CC_FLAGS_FTRACE)
> > > > +endif
> > > > +
> > >
> > > Can you narrow it down further? That is, do you really need all of the
> > > above to stop the stalls?
> >
> > I tried to reduce it to 1 or combinations of 2 files only, but that
> > didn't work.
>
> I'm curious if this would help at all?
>
>
> diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c
> index 2a52f42f64b6..d020ecefd151 100644
> --- a/kernel/rcu/tree.c
> +++ b/kernel/rcu/tree.c
> @@ -1094,7 +1094,7 @@ static void rcu_disable_urgency_upon_qs(struct rcu_data *rdp)
>   * if the current CPU is not in its idle loop or is in an interrupt or
>   * NMI handler, return true.
>   */
> -bool rcu_is_watching(void)
> +notrace bool rcu_is_watching(void)
>  {
>         bool ret;
>
> Although I don't see it in the recursion list.

It seems a patch to that effect is already in -next ("rcu,ftrace: Fix
ftrace recursion"), and my experiments so far have all been with it.

Thanks,
-- Marco