From 96b9c592def5d7203bdad1337d9c92a2183de5cb Mon Sep 17 00:00:00 2001 From: Roman Gushchin Date: Fri, 26 Apr 2019 10:59:45 -0700 Subject: [PATCH] cgroup: get rid of cgroup_freezer_frozen_exit() A task should never enter the exit path with the task->frozen bit set. Any frozen task must enter the signal handling loop and the only way to escape is through cgroup_leave_frozen(true), which unconditionally drops the task->frozen bit. So it means that cgroyp_freezer_frozen_exit() has zero chances to be called and has to be removed. Let's put a WARN_ON_ONCE() instead of the cgroup_freezer_frozen_exit() call to catch any potential leak of the task's frozen bit. Suggested-by: Oleg Nesterov Signed-off-by: Roman Gushchin Signed-off-by: Tejun Heo --- include/linux/cgroup.h | 2 +- kernel/cgroup/cgroup.c | 5 ++--- kernel/cgroup/freezer.c | 10 ---------- 3 files changed, 3 insertions(+), 14 deletions(-) diff --git a/include/linux/cgroup.h b/include/linux/cgroup.h index 3e2efd4..c0077ad 100644 --- a/include/linux/cgroup.h +++ b/include/linux/cgroup.h @@ -889,7 +889,7 @@ void cgroup_update_frozen(struct cgroup *cgrp); void cgroup_freeze(struct cgroup *cgrp, bool freeze); void cgroup_freezer_migrate_task(struct task_struct *task, struct cgroup *src, struct cgroup *dst); -void cgroup_freezer_frozen_exit(struct task_struct *task); + static inline bool cgroup_task_freeze(struct task_struct *task) { bool ret; diff --git a/kernel/cgroup/cgroup.c b/kernel/cgroup/cgroup.c index 4fe9f7f..327f37c 100644 --- a/kernel/cgroup/cgroup.c +++ b/kernel/cgroup/cgroup.c @@ -5926,9 +5926,8 @@ void cgroup_exit(struct task_struct *tsk) css_set_move_task(tsk, cset, NULL, false); cset->nr_tasks--; - if (unlikely(cgroup_task_frozen(tsk))) - cgroup_freezer_frozen_exit(tsk); - else if (unlikely(cgroup_task_freeze(tsk))) + WARN_ON_ONCE(cgroup_task_frozen(tsk)); + if (unlikely(cgroup_task_freeze(tsk))) cgroup_update_frozen(task_dfl_cgroup(tsk)); spin_unlock_irq(&css_set_lock); diff --git a/kernel/cgroup/freezer.c b/kernel/cgroup/freezer.c index c321e76..8cf0106 100644 --- a/kernel/cgroup/freezer.c +++ b/kernel/cgroup/freezer.c @@ -248,16 +248,6 @@ void cgroup_freezer_migrate_task(struct task_struct *task, cgroup_freeze_task(task, test_bit(CGRP_FREEZE, &dst->flags)); } -void cgroup_freezer_frozen_exit(struct task_struct *task) -{ - struct cgroup *cgrp = task_dfl_cgroup(task); - - lockdep_assert_held(&css_set_lock); - - cgroup_dec_frozen_cnt(cgrp); - cgroup_update_frozen(cgrp); -} - void cgroup_freeze(struct cgroup *cgrp, bool freeze) { struct cgroup_subsys_state *css; -- 2.7.4