From: Thomas Gleixner <tglx@linutronix.de>
Date: Tue, 31 May 2011 16:59:16 +0200
Subject: sched: Move task_struct cleanup to RCU
Git-repo: git://git.kernel.org/pub/scm/linux/kernel/git/rt/linux-rt-devel.git
Git-commit: 4394af581fe9eea0b0a3a2f2a92bd52891f8e403
Patch-mainline: Queued in subsystem maintainer repository
References: SLE Realtime Extension

__put_task_struct() does quite some expensive work. We don't want to
burden random tasks with that.

Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Mike Galbraith <mgalbraith@suse.de>
---
 include/linux/sched.h      |    3 +++
 include/linux/sched/task.h |   10 ++++++++++
 kernel/fork.c              |   15 ++++++++++++++-
 3 files changed, 27 insertions(+), 1 deletion(-)

--- a/include/linux/sched.h
+++ b/include/linux/sched.h
@@ -1062,6 +1062,9 @@ struct task_struct {
 	unsigned int			sequential_io;
 	unsigned int			sequential_io_avg;
 #endif
+#ifdef CONFIG_PREEMPT_RT_BASE
+	struct rcu_head			put_rcu;
+#endif
 #ifdef CONFIG_DEBUG_ATOMIC_SLEEP
 	unsigned long			task_state_change;
 #endif
--- a/include/linux/sched/task.h
+++ b/include/linux/sched/task.h
@@ -86,6 +86,15 @@ extern void sched_exec(void);
 
 #define get_task_struct(tsk) do { atomic_inc(&(tsk)->usage); } while(0)
 
+#ifdef CONFIG_PREEMPT_RT_BASE
+extern void __put_task_struct_cb(struct rcu_head *rhp);
+
+static inline void put_task_struct(struct task_struct *t)
+{
+	if (atomic_dec_and_test(&t->usage))
+		call_rcu(&t->put_rcu, __put_task_struct_cb);
+}
+#else
 extern void __put_task_struct(struct task_struct *t);
 
 static inline void put_task_struct(struct task_struct *t)
@@ -93,6 +102,7 @@ static inline void put_task_struct(struc
 	if (atomic_dec_and_test(&t->usage))
 		__put_task_struct(t);
 }
+#endif
 
 struct task_struct *task_rcu_dereference(struct task_struct **ptask);
 struct task_struct *try_get_task_struct(struct task_struct **ptask);
--- a/kernel/fork.c
+++ b/kernel/fork.c
@@ -402,7 +402,9 @@ static inline void put_signal_struct(str
 	if (atomic_dec_and_test(&sig->sigcnt))
 		free_signal_struct(sig);
 }
-
+#ifdef CONFIG_PREEMPT_RT_BASE
+static
+#endif
 void __put_task_struct(struct task_struct *tsk)
 {
 	WARN_ON(!tsk->exit_state);
@@ -419,7 +421,18 @@ void __put_task_struct(struct task_struc
 	if (!profile_handoff_task(tsk))
 		free_task(tsk);
 }
+#ifndef CONFIG_PREEMPT_RT_BASE
 EXPORT_SYMBOL_GPL(__put_task_struct);
+#else
+void __put_task_struct_cb(struct rcu_head *rhp)
+{
+	struct task_struct *tsk = container_of(rhp, struct task_struct, put_rcu);
+
+	__put_task_struct(tsk);
+
+}
+EXPORT_SYMBOL_GPL(__put_task_struct_cb);
+#endif
 
 void __init __weak arch_task_cache_init(void) { }