Revert "sched: Fix yet more sched_fork() races"

hulk inclusion
category: bugfix
bugzilla: 186973, https://gitee.com/openeuler/kernel/issues/I5CA6K
CVE: NA

--------------------------------

This reverts commit af98db5f.
the patch af98db5f("sched: Fix yet more sched_fork()") may
be cause a process sleep at cgroup_post_fork()->freezer_fork()
while taking group_threadgroup_rwsem lock long time, it cause
a problem that other tasks will wait while fork child process
and the system will stall.
Signed-off-by: NZhang Qiao <zhangqiao22@huawei.com>
Reviewed-by: NChen Hui <judy.chenhui@huawei.com>
Signed-off-by: NYongqiang Liu <liuyongqiang13@huawei.com>

include/linux/sched/task.h

@@ -33,7 +33,7 @@ extern asmlinkage void schedule_tail(struct task_struct *prev);
 extern void init_idle(struct task_struct *idle, int cpu);
 
 extern int sched_fork(unsigned long clone_flags, struct task_struct *p);
-extern void sched_cgroup_fork(struct task_struct *p);
+extern void sched_post_fork(struct task_struct *p);
 extern void sched_dead(struct task_struct *p);
 
 void __noreturn do_task_dead(void);

kernel/fork.c

@@ -2063,17 +2063,6 @@ static __latent_entropy struct task_struct *copy_process(
 	if (retval)
 		goto bad_fork_free_futex_mutex;
 
-	/*
-	 * Now that the cgroups are pinned, re-clone the parent cgroup and put
-	 * the new task on the correct runqueue. All this *before* the task
-	 * becomes visible.
-	 *
-	 * This isn't part of ->can_fork() because while the re-cloning is
-	 * cgroup specific, it unconditionally needs to place the task on a
-	 * runqueue.
-	 */
-	sched_cgroup_fork(p);
-
 	/*
 	 * From this point on we must avoid any synchronous user-space
 	 * communication until we take the tasklist-lock. In particular, we do
@@ -2182,6 +2171,7 @@ static __latent_entropy struct task_struct *copy_process(
 
 	proc_fork_connector(p);
 	cgroup_post_fork(p);
+	sched_post_fork(p);
 	cgroup_threadgroup_change_end(current);
 	perf_event_fork(p);
 

kernel/sched/core.c

@@ -2357,9 +2357,8 @@ int sched_fork(unsigned long clone_flags, struct task_struct *p)
 	return 0;
 }
 
-void sched_cgroup_fork(struct task_struct *p)
+void sched_post_fork(struct task_struct *p)
 {
-
 	unsigned long flags;
 
 	/*
@@ -2370,9 +2369,6 @@ void sched_cgroup_fork(struct task_struct *p)
 	 * Silence PROVE_RCU.
 	 */
 	raw_spin_lock_irqsave(&p->pi_lock, flags);
-#ifdef CONFIG_CGROUP_SCHED
-	p->sched_task_group = task_group(current);
- #endif
 	rseq_migrate(p);
 	/*
 	 * We're setting the CPU for the first time, we don't migrate,