tree 65b6a47aabaa91a19d1f0c01a613d73ab3cecee3
parent 53254f900bd9ff1e3cc5628e76126bb403d9d160
author Oleg Nesterov <oleg@redhat.com> 1448650639 +0100
committer Tejun Heo <tj@kernel.org> 1448894898 -0500

cgroup: pids: fix race between cgroup_post_fork() and cgroup_migrate()

If the new child migrates to another cgroup before cgroup_post_fork() calls
subsys->fork(), then both pids_can_attach() and pids_fork() will do the same
pids_uncharge(old_pids) + pids_charge(pids) sequence twice.

Change copy_process() to call threadgroup_change_begin/threadgroup_change_end
unconditionally. percpu_down_read() is cheap and this allows other cleanups,
see the next changes.

Also, this way we can unify cgroup_threadgroup_rwsem and dup_mmap_sem.

Signed-off-by: Oleg Nesterov <oleg@redhat.com>
Acked-by: Zefan Li <lizefan@huawei.com>
Signed-off-by: Tejun Heo <tj@kernel.org>