Re: linux-next: stall warnings and deadlock on Arm64 (was: [PATCH] kfence: Avoid stalling...)

[Marco Elver <elver@google.com>]

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