Commit 96b9c592 authored by Roman Gushchin's avatar Roman Gushchin Committed by Tejun Heo
Browse files

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: default avatarOleg Nesterov <oleg@redhat.com>
Signed-off-by: default avatarRoman Gushchin <guro@fb.com>
Signed-off-by: default avatarTejun Heo <tj@kernel.org>
parent cb2c4cd8

include/linux/cgroup.h

+1 −1
Original line number Diff line number Diff line
@@ -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;

kernel/cgroup/cgroup.c

+2 −3
Original line number Diff line number Diff line
@@ -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);

kernel/cgroup/freezer.c

+0 −10
Original line number Diff line number Diff line
@@ -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;

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