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

[Jiri Olsa <jolsa@kernel.org>]

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)
 {
 	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;
 
-- 
2.35.3