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

Gregory Haskins
2008-08-15T12:20:51Z

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