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Subject[PATCH v2 RFC tip/core/rcu 4/4] rcu: Add Kconfig option to expedite grace periods during boot
Date
From: "Paul E. McKenney" <paulmck@linux.vnet.ibm.com>

This commit adds a CONFIG_RCU_EXPEDITE_BOOT Kconfig parameter
that emulates a very early boot rcu_expedite_gp(). A late-boot
call to rcu_end_inkernel_boot() will provide the corresponding
rcu_unexpedite_gp(). The late-boot call to rcu_end_inkernel_boot()
should be made just before init is spawned.

Reported-by: Arjan van de Ven <arjan@linux.intel.com>
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
---
include/linux/rcupdate.h | 1 +
init/Kconfig | 13 +++++++++++++
kernel/rcu/update.c | 11 ++++++++++-
3 files changed, 24 insertions(+), 1 deletion(-)

diff --git a/include/linux/rcupdate.h b/include/linux/rcupdate.h
index 0189ac088c67..573a5afd5ed8 100644
--- a/include/linux/rcupdate.h
+++ b/include/linux/rcupdate.h
@@ -287,6 +287,7 @@ static inline int rcu_preempt_depth(void)

/* Internal to kernel */
void rcu_init(void);
+void rcu_end_inkernel_boot(void);
void rcu_sched_qs(void);
void rcu_bh_qs(void);
void rcu_check_callbacks(int user);
diff --git a/init/Kconfig b/init/Kconfig
index 1354ac09b516..ece7e9380867 100644
--- a/init/Kconfig
+++ b/init/Kconfig
@@ -791,6 +791,19 @@ config RCU_NOCB_CPU_ALL

endchoice

+config RCU_EXPEDITE_BOOT
+ bool
+ default n
+ help
+ This option enables expedited grace periods at boot time,
+ as if rcu_expedite_gp() had been invoked early in boot.
+ The corresponding rcu_unexpedite_gp() is invoked from
+ rcu_end_inkernel_boot(), which is intended to be invoked
+ at the end of the kernel-only boot sequence, just before
+ init is exec'ed.
+
+ Accept the default if unsure.
+
endmenu # "RCU Subsystem"

config BUILD_BIN2C
diff --git a/kernel/rcu/update.c b/kernel/rcu/update.c
index 44a74c24936a..1f133350da01 100644
--- a/kernel/rcu/update.c
+++ b/kernel/rcu/update.c
@@ -64,7 +64,8 @@ module_param(rcu_expedited, int, 0);

#ifndef CONFIG_TINY_RCU

-static atomic_t rcu_expedited_nesting;
+static atomic_t rcu_expedited_nesting =
+ ATOMIC_INIT(IS_ENABLED(CONFIG_RCU_EXPEDITE_BOOT) ? 1 : 0);

/*
* Should normal grace-period primitives be expedited? Intended for
@@ -109,6 +110,14 @@ EXPORT_SYMBOL_GPL(rcu_unexpedite_gp);

#endif /* #ifndef CONFIG_TINY_RCU */

+/*
+ * Inform RCU of the end of the in-kernel boot sequence.
+ */
+void rcu_end_inkernel_boot(void)
+{
+ if (IS_ENABLED(CONFIG_RCU_EXPEDITE_BOOT))
+ rcu_unexpedite_gp();
+}

#ifdef CONFIG_PREEMPT_RCU

--
1.8.1.5


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