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...@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.k...@canonical.com>
Many thanks!
