[PATCH] rcu: Make rcu_normal_after_boot writable on RT

[Juri Lelli]

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, 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.

Signed-off-by: Juri Lelli <juri.lelli@xxxxxxxxxx>
---
 kernel/rcu/update.c | 2 --
 1 file changed, 2 deletions(-)

diff --git a/kernel/rcu/update.c b/kernel/rcu/update.c
index c21b38cc25e9..0fdbf937edac 100644
--- a/kernel/rcu/update.c
+++ b/kernel/rcu/update.c
@@ -57,9 +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
 module_param(rcu_normal_after_boot, int, 0);
-#endif
 #endif /* #ifndef CONFIG_TINY_RCU */
 
 #ifdef CONFIG_DEBUG_LOCK_ALLOC
-- 
2.31.1