Merge tag 'cgroup-for-6.0-rc2-fixes-2' of git://git.kernel.org/pub/scm/linux/kernel/git/tj/cgroup

Pull another cgroup fix from Tejun Heo:
 "Commit 4f7e723 ("cgroup: Fix threadgroup_rwsem <->
  cpus_read_lock() deadlock") required the cgroup
  core to grab cpus_read_lock() before invoking ->attach().

  Unfortunately, it missed adding cpus_read_lock() in
  cgroup_attach_task_all(). Fix it"

* tag 'cgroup-for-6.0-rc2-fixes-2' of git://git.kernel.org/pub/scm/linux/kernel/git/tj/cgroup:
  cgroup: Add missing cpus_read_lock() to cgroup_attach_task_all()

Author: torvalds

kernel/cgroup/cgroup-v1.c

@@ -59,6 +59,7 @@ int cgroup_attach_task_all(struct task_struct *from, struct task_struct *tsk)
 	int retval = 0;
 
 	mutex_lock(&cgroup_mutex);
+	cpus_read_lock();
 	percpu_down_write(&cgroup_threadgroup_rwsem);
 	for_each_root(root) {
 		struct cgroup *from_cgrp;
@@ -72,6 +73,7 @@ int cgroup_attach_task_all(struct task_struct *from, struct task_struct *tsk)
 			break;
 	}
 	percpu_up_write(&cgroup_threadgroup_rwsem);
+	cpus_read_unlock();
 	mutex_unlock(&cgroup_mutex);
 
 	return retval;