From: Thomas Gleixner <tglx@linutronix.de>
Date: Tue, 31 May 2011 16:59:16 +0200
Subject: [PATCH 105/351] sched: Move task_struct cleanup to RCU
Origin: https://git.kernel.org/cgit/linux/kernel/git/rt/linux-stable-rt.git/commit?id=4a264f82c1ecb578701edbdf97f8d040ad1f9cba

__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>
---
 include/linux/sched.h      |  3 +++
 include/linux/sched/task.h | 11 ++++++++++-
 kernel/fork.c              | 15 ++++++++++++++-
 3 files changed, 27 insertions(+), 2 deletions(-)

diff --git a/include/linux/sched.h b/include/linux/sched.h
index 92faffe9ecf0..d627469bab35 100644
--- a/include/linux/sched.h
+++ b/include/linux/sched.h
@@ -1200,6 +1200,9 @@ 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
diff --git a/include/linux/sched/task.h b/include/linux/sched/task.h
index 91401309b1aa..5f8c1d53bc11 100644
--- a/include/linux/sched/task.h
+++ b/include/linux/sched/task.h
@@ -90,6 +90,15 @@ 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)
@@ -97,7 +106,7 @@ static inline void put_task_struct(struct task_struct *t)
 	if (atomic_dec_and_test(&t->usage))
 		__put_task_struct(t);
 }
-
+#endif
 struct task_struct *task_rcu_dereference(struct task_struct **ptask);
 
 #ifdef CONFIG_ARCH_WANTS_DYNAMIC_TASK_STRUCT
diff --git a/kernel/fork.c b/kernel/fork.c
index c27c196fd70e..f5a4c42233f0 100644
--- a/kernel/fork.c
+++ b/kernel/fork.c
@@ -676,7 +676,9 @@ static inline void put_signal_struct(struct signal_struct *sig)
 	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);
@@ -693,7 +695,18 @@ void __put_task_struct(struct task_struct *tsk)
 	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) { }