Re: [PATCH bpf-next 1/2] cpuidle/rcu: Making arch_cpu_idle and rcu_idle_exit noinstr

Yonghong Song
2022-05-17T02:55:02Z

On 5/15/22 1:36 PM, Jiri Olsa wrote:
> Making arch_cpu_idle and rcu_idle_exit noinstr. Both functions run
> in rcu 'not watching' context and if there's tracer attached to
> them, which uses rcu (e.g. kprobe multi interface) it will hit RCU
> warning like:
>
> [ 3.017540] WARNING: suspicious RCU usage
> ...
> [ 3.018363] kprobe_multi_link_handler+0x68/0x1c0
> [ 3.018364] ? kprobe_multi_link_handler+0x3e/0x1c0
> [ 3.018366] ? arch_cpu_idle_dead+0x10/0x10
> [ 3.018367] ? arch_cpu_idle_dead+0x10/0x10
> [ 3.018371] fprobe_handler.part.0+0xab/0x150
> [ 3.018374] 0xffffffffa00080c8
> [ 3.018393] ? arch_cpu_idle+0x5/0x10
> [ 3.018398] arch_cpu_idle+0x5/0x10
> [ 3.018399] default_idle_call+0x59/0x90
> [ 3.018401] do_idle+0x1c3/0x1d0
>
> The call path is following:
>
> default_idle_call
> rcu_idle_enter
> arch_cpu_idle
> rcu_idle_exit
>
> The arch_cpu_idle and rcu_idle_exit are the only ones from above
> path that are traceble and cause this problem on my setup.
>
> Signed-off-by: Jiri Olsa <jolsa@kernel.org>
> ---
> arch/x86/kernel/process.c | 2 +-
> kernel/rcu/tree.c | 2 +-
> 2 files changed, 2 insertions(+), 2 deletions(-)
>
> diff --git a/arch/x86/kernel/process.c b/arch/x86/kernel/process.c
> index b370767f5b19..1345cb0124a6 100644
> --- a/arch/x86/kernel/process.c
> +++ b/arch/x86/kernel/process.c
> @@ -720,7 +720,7 @@ void arch_cpu_idle_dead(void)
> /*
> * Called from the generic idle code.
> */
> -void arch_cpu_idle(void)
> +void noinstr arch_cpu_idle(void)

noinstr includes a lot of attributes:

#define noinstr \
noinline notrace __attribute((__section__(".noinstr.text"))) \
__no_kcsan __no_sanitize_address __no_profile
__no_sanitize_coverage

should we use notrace here?

> {
> x86_idle();
> }
> diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c
> index a4b8189455d5..20d529722f51 100644
> --- a/kernel/rcu/tree.c
> +++ b/kernel/rcu/tree.c
> @@ -896,7 +896,7 @@ static void noinstr rcu_eqs_exit(bool user)
> * If you add or remove a call to rcu_idle_exit(), be sure to test with
> * CONFIG_RCU_EQS_DEBUG=y.
> */
> -void rcu_idle_exit(void)
> +void noinstr rcu_idle_exit(void)
> {
> unsigned long flags;
>