rcu: Add synchronize_sched_expedited() primitive

This adds the synchronize_sched_expedited() primitive that
implements the "big hammer" expedited RCU grace periods.

This primitive is placed in kernel/sched.c rather than
kernel/rcupdate.c due to its need to interact closely with the
migration_thread() kthread.

The idea is to wake up this kthread with req->task set to NULL,
in response to which the kthread reports the quiescent state
resulting from the kthread having been scheduled.

Because this patch needs to fallback to the slow versions of
the primitives in response to some races with CPU onlining and
offlining, a new synchronize_rcu_bh() primitive is added as
well.

Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Cc: akpm@linux-foundation.org
Cc: torvalds@linux-foundation.org
Cc: davem@davemloft.net
Cc: dada1@cosmosbay.com
Cc: zbr@ioremap.net
Cc: jeff.chua.linux@gmail.com
Cc: paulus@samba.org
Cc: laijs@cn.fujitsu.com
Cc: jengelh@medozas.de
Cc: r000n@r000n.net
Cc: benh@kernel.crashing.org
Cc: mathieu.desnoyers@polymtl.ca
LKML-Reference: <12459460982947-git-send-email->
Signed-off-by: Ingo Molnar <mingo@elte.hu>

1 files changed, 11 insertions, 1 deletions

diff --git a/include/linux/rcutree.h b/include/linux/rcutree.h
index 5a5153806c42..d4dfd2489633 100644
--- a/include/linux/rcutree.h
+++ b/include/linux/rcutree.h
@@ -286,8 +286,14 @@ static inline void __rcu_read_unlock_bh(void)
 
 #define call_rcu_sched(head, func) call_rcu(head, func)
 
-static inline void rcu_init_sched(void)
+static inline void synchronize_rcu_expedited(void)
+{
+	synchronize_sched_expedited();
+}
+
+static inline void synchronize_rcu_bh_expedited(void)
 {
+	synchronize_sched_expedited();
 }
 
 extern void __rcu_init(void);
@@ -297,6 +303,10 @@ extern void rcu_restart_cpu(int cpu);
 extern long rcu_batches_completed(void);
 extern long rcu_batches_completed_bh(void);
 
+static inline void rcu_init_sched(void)
+{
+}
+
 #ifdef CONFIG_NO_HZ
 void rcu_enter_nohz(void);
 void rcu_exit_nohz(void);