tree acda9f1d18f4266bb7a90a8e307328fe9aef58f0
parent e9bad0a8967987edae58ad498b7ba5ba91923e1e
author Tejun Heo <tj@kernel.org> 1634674347 -1000
committer Tejun Heo <tj@kernel.org> 1634757785 -1000

sched, cgroup: Generalize threadgroup_rwsem

Generalize threadgroup stabilization through threadgroup_rwsem so that it
can be used outside cgroup.

* A new config option CONFIG_THREADGROUP_RWSEM which is selected by
  CONFIG_CGROUPS enables threadgroup_rwsem.

* The declarations are moved to linux/sched/threadgroup_rwsem.h and the
  rwsem is now defined in kernel/sched/core.c.

* cgroup_mutex nests outside threadgroup_rwsem. During fork,
  cgroup_css_set_fork() which is called from cgroup_can_fork() was acquiring
  both. However, generalizing threadgroup_rwsem means that it needs to be
  acquired and released in the outer copy_process(). To maintain the locking
  order, break out cgroup_mutex acquisition into a separate function
  cgroup_prep_fork() which is called from copy_process() before acquiring
  threadgroup_rwsem.

No functional changes.

Signed-off-by: Tejun Heo <tj@kernel.org>
Cc: Christian Brauner <christian.brauner@ubuntu.com>