Re: [PATCH bpf-next 1/2] cpuidle/rcu: Making arch_cpu_idle and rcu_idle_exit noinstr
From: "Paul E. McKenney" <paulmck@kernel.org>
Date: 2022-05-16 04:25:49
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On Sun, May 15, 2022 at 10:36:52PM +0200, 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>
From an RCU viewpoint: Reviewed-by: Paul E. McKenney <paulmck@kernel.org> [ I considered asking for an instrumentation_on() in rcu_idle_exit(), but there is no point given that local_irq_restore() isn't something you instrument anyway. ]
quoted hunk ↗ jump to hunk
--- 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