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cgroup: get rid of cgroup_freezer_frozen_exit()

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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 <oleg@redhat.com>
Signed-off-by: Roman Gushchin <guro@fb.com>
Signed-off-by: Tejun Heo <tj@kernel.org>
This commit is contained in:
Roman Gushchin 2019-04-26 10:59:45 -07:00 committed by Tejun Heo
parent cb2c4cd878
commit 96b9c592de
3 changed files with 3 additions and 14 deletions
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2
include/linux/cgroup.h
View File

@ -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;

5
kernel/cgroup/cgroup.c
View File

@ -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);

10
kernel/cgroup/freezer.c
View File

@ -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;