1 files changed, 29 insertions, 2 deletions

diff --git a/include/linux/sched/task.h b/include/linux/sched/task.h
index 36f3011ab601..e3c20a4f81f5 100644
--- a/include/linux/sched/task.h
+++ b/include/linux/sched/task.h
@@ -51,7 +51,9 @@ extern int sched_fork(unsigned long clone_flags, struct task_struct *p);
 extern void sched_dead(struct task_struct *p);
 
 void __noreturn do_task_dead(void);
+void __noreturn make_task_dead(int signr);
 
+extern void mm_cache_init(void);
 extern void proc_caches_init(void);
 
 extern void fork_init(void);
@@ -92,7 +94,6 @@ extern long _do_fork(struct kernel_clone_args *kargs);
 extern bool legacy_clone_args_valid(const struct kernel_clone_args *kargs);
 extern long do_fork(unsigned long, unsigned long, unsigned long, int __user *, int __user *);
 struct task_struct *fork_idle(int);
-struct mm_struct *copy_init_mm(void);
 extern pid_t kernel_thread(int (*fn)(void *), void *arg, unsigned long flags);
 extern long kernel_wait4(pid_t, int __user *, int, struct rusage *);
 
@@ -112,10 +113,36 @@ static inline struct task_struct *get_task_struct(struct task_struct *t)
 }
 
 extern void __put_task_struct(struct task_struct *t);
+extern void __put_task_struct_rcu_cb(struct rcu_head *rhp);
 
 static inline void put_task_struct(struct task_struct *t)
 {
-	if (refcount_dec_and_test(&t->usage))
+	if (!refcount_dec_and_test(&t->usage))
+		return;
+
+	/*
+	 * under PREEMPT_RT, we can't call put_task_struct
+	 * in atomic context because it will indirectly
+	 * acquire sleeping locks.
+	 *
+	 * call_rcu() will schedule delayed_put_task_struct_rcu()
+	 * to be called in process context.
+	 *
+	 * __put_task_struct() is called when
+	 * refcount_dec_and_test(&t->usage) succeeds.
+	 *
+	 * This means that it can't "conflict" with
+	 * put_task_struct_rcu_user() which abuses ->rcu the same
+	 * way; rcu_users has a reference so task->usage can't be
+	 * zero after rcu_users 1 -> 0 transition.
+	 *
+	 * delayed_free_task() also uses ->rcu, but it is only called
+	 * when it fails to fork a process. Therefore, there is no
+	 * way it can conflict with put_task_struct().
+	 */
+	if (IS_ENABLED(CONFIG_PREEMPT_RT) && !preemptible())
+		call_rcu(&t->rcu, __put_task_struct_rcu_cb);
+	else
 		__put_task_struct(t);
 }