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-rw-r--r--arch/Kconfig10
-rw-r--r--include/linux/rcupdate.h9
-rw-r--r--init/Kconfig10
-rw-r--r--kernel/rcutree.c5
4 files changed, 33 insertions, 1 deletions
diff --git a/arch/Kconfig b/arch/Kconfig
index 72f2fa189cc5..1401a7587973 100644
--- a/arch/Kconfig
+++ b/arch/Kconfig
@@ -281,4 +281,14 @@ config SECCOMP_FILTER
See Documentation/prctl/seccomp_filter.txt for details.
+config HAVE_RCU_USER_QS
+ bool
+ help
+ Provide kernel entry/exit hooks necessary for userspace
+ RCU extended quiescent state. Syscalls need to be wrapped inside
+ rcu_user_exit()-rcu_user_enter() through the slow path using
+ TIF_NOHZ flag. Exceptions handlers must be wrapped as well. Irqs
+ are already protected inside rcu_irq_enter/rcu_irq_exit() but
+ preemption or signal handling on irq exit still need to be protected.
+
source "kernel/gcov/Kconfig"
diff --git a/include/linux/rcupdate.h b/include/linux/rcupdate.h
index f818dd165b44..f5034f22e94b 100644
--- a/include/linux/rcupdate.h
+++ b/include/linux/rcupdate.h
@@ -191,10 +191,19 @@ extern void rcu_idle_enter(void);
extern void rcu_idle_exit(void);
extern void rcu_irq_enter(void);
extern void rcu_irq_exit(void);
+
+#ifdef CONFIG_RCU_USER_QS
extern void rcu_user_enter(void);
extern void rcu_user_exit(void);
extern void rcu_user_enter_after_irq(void);
extern void rcu_user_exit_after_irq(void);
+#else
+static inline void rcu_user_enter(void) { }
+static inline void rcu_user_exit(void) { }
+static inline void rcu_user_enter_after_irq(void) { }
+static inline void rcu_user_exit_after_irq(void) { }
+#endif /* CONFIG_RCU_USER_QS */
+
extern void exit_rcu(void);
/**
diff --git a/init/Kconfig b/init/Kconfig
index af6c7f8ba019..f6a1830165ce 100644
--- a/init/Kconfig
+++ b/init/Kconfig
@@ -441,6 +441,16 @@ config PREEMPT_RCU
This option enables preemptible-RCU code that is common between
the TREE_PREEMPT_RCU and TINY_PREEMPT_RCU implementations.
+config RCU_USER_QS
+ bool "Consider userspace as in RCU extended quiescent state"
+ depends on HAVE_RCU_USER_QS && SMP
+ help
+ This option sets hooks on kernel / userspace boundaries and
+ puts RCU in extended quiescent state when the CPU runs in
+ userspace. It means that when a CPU runs in userspace, it is
+ excluded from the global RCU state machine and thus doesn't
+ to keep the timer tick on for RCU.
+
config RCU_FANOUT
int "Tree-based hierarchical RCU fanout value"
range 2 64 if 64BIT
diff --git a/kernel/rcutree.c b/kernel/rcutree.c
index 4138f59fa2f4..79fa2db1595b 100644
--- a/kernel/rcutree.c
+++ b/kernel/rcutree.c
@@ -400,6 +400,7 @@ void rcu_idle_enter(void)
}
EXPORT_SYMBOL_GPL(rcu_idle_enter);
+#ifdef CONFIG_RCU_USER_QS
/**
* rcu_user_enter - inform RCU that we are resuming userspace.
*
@@ -424,7 +425,6 @@ void rcu_user_enter(void)
rcu_eqs_enter(1);
}
-
/**
* rcu_user_enter_after_irq - inform RCU that we are going to resume userspace
* after the current irq returns.
@@ -445,6 +445,7 @@ void rcu_user_enter_after_irq(void)
rdtp->dynticks_nesting = 1;
local_irq_restore(flags);
}
+#endif /* CONFIG_RCU_USER_QS */
/**
* rcu_irq_exit - inform RCU that current CPU is exiting irq towards idle
@@ -548,6 +549,7 @@ void rcu_idle_exit(void)
}
EXPORT_SYMBOL_GPL(rcu_idle_exit);
+#ifdef CONFIG_RCU_USER_QS
/**
* rcu_user_exit - inform RCU that we are exiting userspace.
*
@@ -591,6 +593,7 @@ void rcu_user_exit_after_irq(void)
rdtp->dynticks_nesting += DYNTICK_TASK_EXIT_IDLE;
local_irq_restore(flags);
}
+#endif /* CONFIG_RCU_USER_QS */
/**
* rcu_irq_enter - inform RCU that current CPU is entering irq away from idle