From ebb6d30d9ed1fe7137486e1be2ae9d621e918c4a Mon Sep 17 00:00:00 2001 From: Juri Lelli Date: Tue, 10 Aug 2021 10:48:15 +0200 Subject: [PATCH] rcu: Make rcu_normal_after_boot writable again Certain configurations (e.g., systems that make heavy use of netns) need to use synchronize_rcu_expedited() to service RCU grace periods even after boot. Even though synchronize_rcu_expedited() has been traditionally considered harmful for RT for the heavy use of IPIs, it is perfectly usable under certain conditions (e.g. nohz_full). Make rcupdate.rcu_normal_after_boot= again writeable on RT (if NO_HZ_ FULL is defined), but keep its default value to 1 (enabled) to avoid regressions. Users who need synchronize_rcu_expedited() will boot with rcupdate.rcu_normal_after_ boot=0 in the kernel cmdline. Reflect the change in synchronize_rcu_expedited_wait() by removing the WARN related to CONFIG_PREEMPT_RT. Signed-off-by: Juri Lelli Signed-off-by: Paul E. McKenney --- kernel/rcu/tree_exp.h | 1 - kernel/rcu/update.c | 2 +- 2 files changed, 1 insertion(+), 2 deletions(-) diff --git a/kernel/rcu/tree_exp.h b/kernel/rcu/tree_exp.h index 2796084ef85a..d9e4f8eb9ae2 100644 --- a/kernel/rcu/tree_exp.h +++ b/kernel/rcu/tree_exp.h @@ -512,7 +512,6 @@ static void synchronize_rcu_expedited_wait(void) j = READ_ONCE(jiffies_till_first_fqs); if (synchronize_rcu_expedited_wait_once(j + HZ)) return; - WARN_ON_ONCE(IS_ENABLED(CONFIG_PREEMPT_RT)); } for (;;) { diff --git a/kernel/rcu/update.c b/kernel/rcu/update.c index c21b38cc25e9..bd551134e2f4 100644 --- a/kernel/rcu/update.c +++ b/kernel/rcu/update.c @@ -57,7 +57,7 @@ module_param(rcu_expedited, int, 0); module_param(rcu_normal, int, 0); static int rcu_normal_after_boot = IS_ENABLED(CONFIG_PREEMPT_RT); -#ifndef CONFIG_PREEMPT_RT +#if !defined(CONFIG_PREEMPT_RT) || defined(CONFIG_NO_HZ_FULL) module_param(rcu_normal_after_boot, int, 0); #endif #endif /* #ifndef CONFIG_TINY_RCU */ -- 2.11.0