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From:   Greg Kroah-Hartman <gregkh@linuxfoundation.org>
To:     linux-kernel@vger.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        stable@vger.kernel.org, Tejun Heo <tj@kernel.org>,
        Oleg Nesterov <oleg@redhat.com>
Subject: [PATCH 4.19 40/45] cgroup: Call cgroup_release() before __exit_signal()
Date:   Thu,  8 Aug 2019 21:05:26 +0200
Message-Id: <20190808190456.128759505@linuxfoundation.org>
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From: Tejun Heo <tj@kernel.org>

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@kernel.org>
Cc: Oleg Nesterov <oleg@redhat.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

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

--- a/kernel/exit.c
+++ b/kernel/exit.c
@@ -194,6 +194,7 @@ repeat:
 	rcu_read_unlock();
 
 	proc_flush_task(p);
+	cgroup_release(p);
 
 	write_lock_irq(&tasklist_lock);
 	ptrace_release_task(p);
@@ -219,7 +220,6 @@ repeat:
 	}
 
 	write_unlock_irq(&tasklist_lock);
-	cgroup_release(p);
 	release_thread(p);
 	call_rcu(&p->rcu, delayed_put_task_struct);