oom, oom_reaper: allow to reap mm shared by the kthreads
oom reaper was skipped for an mm which is shared with the kernel thread
(aka use_mm()). The primary concern was that such a kthread might want
to read from the userspace memory and see zero page as a result of the
oom reaper action. This seems to be overly conservative because none of
the current use_mm() users need to do copy_from_user or get_user. aio
code used to rely on copy_from_user but this is long gone along with
use_mm() usage in fs/aio.c.
We currently have only 3 users in the kernel:
- ffs_user_copy_worker, ep_user_copy_worker only do copy_to_iter()
- vhost_worker needs to copy from userspace but it relies on the
safe __get_user_mm, copy_from_user_mm resp. copy_from_iter_mm
Add a note to use_mm about the copy_from_user risk and allow the oom
killer to invoke the oom_reaper for mms shared with kthreads. This will
practically cause all the sane use cases to be reapable.
Signed-off-by: Michal Hocko <mhocko@suse.com>
2 files changed
