[PATCH RT RFC v2 3/8] sched: rework task reference counting to work with the pi infrastructure

[Gregory Haskins <ghaskins@xxxxxxxxxx>]

Signed-off-by: Gregory Haskins <ghaskins@xxxxxxxxxx>
---

 include/linux/sched.h |    5 +++--
 kernel/fork.c         |   32 +++++++++++++++-----------------
 kernel/sched.c        |   23 +++++++++++++++++++++++
 3 files changed, 41 insertions(+), 19 deletions(-)

diff --git a/include/linux/sched.h b/include/linux/sched.h
index 63ddd1f..9132b42 100644
--- a/include/linux/sched.h
+++ b/include/linux/sched.h
@@ -1305,6 +1305,8 @@ struct task_struct {
 		struct pi_node node;
 		struct pi_sink snk;  /* registered to 'this' to get updates */
 		int prio;
+		struct rcu_head rcu; /* for destruction cleanup */
+
 	} pi;
 
 #ifdef CONFIG_RT_MUTEXES
@@ -1633,12 +1635,11 @@ static inline void put_task_struct(struct task_struct *t)
 		call_rcu(&t->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)
 {
 	if (atomic_dec_and_test(&t->usage))
-		__put_task_struct(t);
+		pi_dropref(&t->pi.node, 0);
 }
 #endif
 
diff --git a/kernel/fork.c b/kernel/fork.c
index 399a0d0..399a0a9 100644
--- a/kernel/fork.c
+++ b/kernel/fork.c
@@ -130,39 +130,37 @@ void free_task(struct task_struct *tsk)
 }
 EXPORT_SYMBOL(free_task);
 
-#ifdef CONFIG_PREEMPT_RT
-void __put_task_struct_cb(struct rcu_head *rhp)
+void prepare_free_task(struct task_struct *tsk)
 {
-	struct task_struct *tsk = container_of(rhp, struct task_struct, rcu);
-
 	BUG_ON(atomic_read(&tsk->usage));
-	WARN_ON(!tsk->exit_state);
 	WARN_ON(tsk == current);
 
+#ifdef CONFIG_PREEMPT_RT
+	WARN_ON(!tsk->exit_state);
+#else
+	WARN_ON(!(tsk->exit_state & (EXIT_DEAD | EXIT_ZOMBIE)));
+#endif
+
 	security_task_free(tsk);
 	free_uid(tsk->user);
 	put_group_info(tsk->group_info);
+
+#ifdef CONFIG_PREEMPT_RT
 	delayacct_tsk_free(tsk);
+#endif
 
 	if (!profile_handoff_task(tsk))
 		free_task(tsk);
 }
 
-#else
-
-void __put_task_struct(struct task_struct *tsk)
+#ifdef CONFIG_PREEMPT_RT
+void __put_task_struct_cb(struct rcu_head *rhp)
 {
-	WARN_ON(!(tsk->exit_state & (EXIT_DEAD | EXIT_ZOMBIE)));
-	BUG_ON(atomic_read(&tsk->usage));
-	WARN_ON(tsk == current);
-
-	security_task_free(tsk);
-	free_uid(tsk->user);
-	put_group_info(tsk->group_info);
+	struct task_struct *tsk = container_of(rhp, struct task_struct, rcu);
 
-	if (!profile_handoff_task(tsk))
-		free_task(tsk);
+	pi_dropref(&tsk->pi.node, 0);
 }
+
 #endif
 
 /*
diff --git a/kernel/sched.c b/kernel/sched.c
index c129b10..729139d 100644
--- a/kernel/sched.c
+++ b/kernel/sched.c
@@ -2370,11 +2370,34 @@ task_pi_boost_cb(struct pi_sink *snk, struct pi_source *src,
 	return 0;
 }
 
+extern void prepare_free_task(struct task_struct *tsk);
+
+static void task_pi_free_rcu(struct rcu_head *rhp)
+{
+	struct task_struct *tsk = container_of(rhp, struct task_struct, pi.rcu);
+
+	prepare_free_task(tsk);
+}
+
+/*
+ * This function is invoked whenever the last references to a task have
+ * been dropped, and we should free the memory on the next rcu grace period
+ */
+static int task_pi_free_cb(struct pi_sink *snk, unsigned int flags)
+{
+	struct task_struct *p = container_of(snk, struct task_struct, pi.snk);
+
+	call_rcu(&p->pi.rcu, task_pi_free_rcu);
+
+	return 0;
+}
+
 static int task_pi_update_cb(struct pi_sink *snk, unsigned int flags);
 
 static struct pi_sink task_pi_sink = {
     .boost = task_pi_boost_cb,
     .update = task_pi_update_cb,
+    .free = task_pi_free_cb,
 };
 
 static inline void

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