[PATCH] stop_machine: Mark functions as notrace

[Zong Li]

On Sat, Oct 24, 2020 at 3:29 AM Colin Ian King <colin.king at canonical.com> wrote:
>
> On 21/10/2020 08:38, Zong Li wrote:
> > Like the commit cb9d7fd51d9f ("watchdog: Mark watchdog touch functions
> > as notrace"), some architectures assume that the stopped CPUs don't make
> > function calls to traceable functions when they are in the stopped
> > state. For example, it causes unexpected kernel crashed when switching
> > tracer on RISC-V.
> >
> > The following patches added calls to these two functions, fix it by
> > adding the notrace annotations.
> >
> > Fixes: 4ecf0a43e729 ("processor: get rid of cpu_relax_yield")
> > Fixes: 366237e7b083 ("stop_machine: Provide RCU quiescent state in
> > multi_cpu_stop()")
> >
> > Signed-off-by: Zong Li <zong.li at sifive.com>
> > ---
> >  kernel/rcu/tree.c     | 2 +-
> >  kernel/stop_machine.c | 2 +-
> >  2 files changed, 2 insertions(+), 2 deletions(-)
> >
> > diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c
> > index 06895ef85d69..2a52f42f64b6 100644
> > --- a/kernel/rcu/tree.c
> > +++ b/kernel/rcu/tree.c
> > @@ -409,7 +409,7 @@ bool rcu_eqs_special_set(int cpu)
> >   *
> >   * The caller must have disabled interrupts and must not be idle.
> >   */
> > -void rcu_momentary_dyntick_idle(void)
> > +notrace void rcu_momentary_dyntick_idle(void)
> >  {
> >       int special;
> >
> > diff --git a/kernel/stop_machine.c b/kernel/stop_machine.c
> > index 865bb0228ab6..890b79cf0e7c 100644
> > --- a/kernel/stop_machine.c
> > +++ b/kernel/stop_machine.c
> > @@ -178,7 +178,7 @@ static void ack_state(struct multi_stop_data *msdata)
> >               set_state(msdata, msdata->state + 1);
> >  }
> >
> > -void __weak stop_machine_yield(const struct cpumask *cpumask)
> > +notrace void __weak stop_machine_yield(const struct cpumask *cpumask)
> >  {
> >       cpu_relax();
> >  }
> >
>
> Apologies for taking so long to reply, I needed to test this on several
> devices.
>
> This not only fixes the ftrace issue I see on RISC-V but also a ftrace
> hang issue on ARM64 in 5.8 too.
>
> Tested-by: Colin Ian King <colin.king at canonical.com>
>
> Many thanks!

Many thanks all for reviewing and testing.

Hi Palmer,
As Steven suggested, could you help to pick up this patch in RISC-V tree?