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>
11 files changed
