cgroup: remove CGRP_WAIT_ON_RMDIR, cgroup_exclude_rmdir() and cgroup_release_and_wakeup_rmdir()

CGRP_WAIT_ON_RMDIR is another kludge which was added to make cgroup
destruction rollback somewhat working.  cgroup_rmdir() used to drain
CSS references and CGRP_WAIT_ON_RMDIR and the associated waitqueue and
helpers were used to allow the task performing rmdir to wait for the
next relevant event.

Unfortunately, the wait is visible to controllers too and the
mechanism got exposed to memcg by 887032670d ("cgroup avoid permanent
sleep at rmdir").

Now that the draining and retries are gone, CGRP_WAIT_ON_RMDIR is
unnecessary.  Remove it and all the mechanisms supporting it.  Note
that memcontrol.c changes are essentially revert of 887032670d
("cgroup avoid permanent sleep at rmdir").

Signed-off-by: Tejun Heo <tj@kernel.org>
Reviewed-by: Michal Hocko <mhocko@suse.cz>
Reviewed-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Acked-by: Li Zefan <lizefan@huawei.com>
Cc: Balbir Singh <bsingharora@gmail.com>

1 files changed, 1 insertions, 23 deletions

diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index 37c356646544..930edfaa5187 100644
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -2681,13 +2681,6 @@ static int mem_cgroup_move_account(struct page *page,
         /* caller should have done css_get */
         pc->mem_cgroup = to;
         mem_cgroup_charge_statistics(to, anon, nr_pages);
-        /*
-         * We charges against "to" which may not have any tasks. Then, "to"
-         * can be under rmdir(). But in current implementation, caller of
-         * this function is just force_empty() and move charge, so it's
-         * guaranteed that "to" is never removed. So, we don't check rmdir
-         * status here.
-         */
         move_unlock_mem_cgroup(from, &flags);
         ret = 0;
 unlock:
@@ -2893,7 +2886,6 @@ __mem_cgroup_commit_charge_swapin(struct page *page, struct mem_cgroup *memcg,
                 return;
         if (!memcg)
                 return;
-        cgroup_exclude_rmdir(&memcg->css);
 
         __mem_cgroup_commit_charge(memcg, page, 1, ctype, true);
         /*
@@ -2907,12 +2899,6 @@ __mem_cgroup_commit_charge_swapin(struct page *page, struct mem_cgroup *memcg,
                 swp_entry_t ent = {.val = page_private(page)};
                 mem_cgroup_uncharge_swap(ent);
         }
-        /*
-         * At swapin, we may charge account against cgroup which has no tasks.
-         * So, rmdir()->pre_destroy() can be called while we do this charge.
-         * In that case, we need to call pre_destroy() again. check it here.
-         */
-        cgroup_release_and_wakeup_rmdir(&memcg->css);
 }
 
 void mem_cgroup_commit_charge_swapin(struct page *page,
@@ -3360,8 +3346,7 @@ void mem_cgroup_end_migration(struct mem_cgroup *memcg,
 
         if (!memcg)
                 return;
-        /* blocks rmdir() */
-        cgroup_exclude_rmdir(&memcg->css);
+
         if (!migration_ok) {
                 used = oldpage;
                 unused = newpage;
@@ -3395,13 +3380,6 @@ void mem_cgroup_end_migration(struct mem_cgroup *memcg,
          */
         if (anon)
                 mem_cgroup_uncharge_page(used);
-        /*
-         * At migration, we may charge account against cgroup which has no
-         * tasks.
-         * So, rmdir()->pre_destroy() can be called while we do this charge.
-         * In that case, we need to call pre_destroy() again. check it here.
-         */
-        cgroup_release_and_wakeup_rmdir(&memcg->css);
 }
 
 /*