[PATCH 4.14 28/33] cgroup: Call cgroup_release() before __exit_signal()

From: Greg Kroah-Hartman
Date: Thu Aug 08 2019 - 15:11:41 EST


From: Tejun Heo <tj@xxxxxxxxxx>

commit 6b115bf58e6f013ca75e7115aabcbd56c20ff31d upstream.

cgroup_release() calls cgroup_subsys->release() which is used by the
pids controller to uncharge its pid. We want to use it to manage
iteration of dying tasks which requires putting it before
__unhash_process(). Move cgroup_release() above __exit_signal().
While this makes it uncharge before the pid is freed, pid is RCU freed
anyway and the window is very narrow.

Signed-off-by: Tejun Heo <tj@xxxxxxxxxx>
Cc: Oleg Nesterov <oleg@xxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>

---
kernel/exit.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)

--- a/kernel/exit.c
+++ b/kernel/exit.c
@@ -193,6 +193,7 @@ repeat:
rcu_read_unlock();

proc_flush_task(p);
+ cgroup_release(p);

write_lock_irq(&tasklist_lock);
ptrace_release_task(p);
@@ -218,7 +219,6 @@ repeat:
}

write_unlock_irq(&tasklist_lock);
- cgroup_release(p);
release_thread(p);
call_rcu(&p->rcu, delayed_put_task_struct);