Commit 9c974c77 authored by Michal Koutný's avatar Michal Koutný Committed by Tejun Heo
Browse files

cgroup: Iterate tasks that did not finish do_exit() 



PF_EXITING is set earlier than actual removal from css_set when a task
is exitting. This can confuse cgroup.procs readers who see no PF_EXITING
tasks, however, rmdir is checking against css_set membership so it can
transitionally fail with EBUSY.

Fix this by listing tasks that weren't unlinked from css_set active
lists.
It may happen that other users of the task iterator (without
CSS_TASK_ITER_PROCS) spot a PF_EXITING task before cgroup_exit(). This
is equal to the state before commit c03cd773 ("cgroup: Include dying
leaders with live threads in PROCS iterations") but it may be reviewed
later.

Reported-by: default avatarSuren Baghdasaryan <surenb@google.com>
Fixes: c03cd773 ("cgroup: Include dying leaders with live threads in PROCS iterations")
Signed-off-by: default avatarMichal Koutný <mkoutny@suse.com>
Signed-off-by: default avatarTejun Heo <tj@kernel.org>
parent 2d4ecb03

include/linux/cgroup.h

+1 −0
Original line number Diff line number Diff line
@@ -62,6 +62,7 @@ struct css_task_iter { 
	struct list_head		*mg_tasks_head;

	struct list_head		*dying_tasks_head;



	struct list_head		*cur_tasks_head;

	struct css_set			*cur_cset;

	struct css_set			*cur_dcset;

	struct task_struct		*cur_task;

kernel/cgroup/cgroup.c

+16 −7
Original line number Diff line number Diff line
@@ -4400,12 +4400,16 @@ static void css_task_iter_advance_css_set(struct css_task_iter *it) 
		}

	} while (!css_set_populated(cset) && list_empty(&cset->dying_tasks));



	if (!list_empty(&cset->tasks))

	if (!list_empty(&cset->tasks)) {

		it->task_pos = cset->tasks.next;

	else if (!list_empty(&cset->mg_tasks))

		it->cur_tasks_head = &cset->tasks;

	} else if (!list_empty(&cset->mg_tasks)) {

		it->task_pos = cset->mg_tasks.next;

	else

		it->cur_tasks_head = &cset->mg_tasks;

	} else {

		it->task_pos = cset->dying_tasks.next;

		it->cur_tasks_head = &cset->dying_tasks;

	}



	it->tasks_head = &cset->tasks;

	it->mg_tasks_head = &cset->mg_tasks;
@@ -4463,10 +4467,14 @@ repeat: 
		else

			it->task_pos = it->task_pos->next;



		if (it->task_pos == it->tasks_head)

		if (it->task_pos == it->tasks_head) {

			it->task_pos = it->mg_tasks_head->next;

		if (it->task_pos == it->mg_tasks_head)

			it->cur_tasks_head = it->mg_tasks_head;

		}

		if (it->task_pos == it->mg_tasks_head) {

			it->task_pos = it->dying_tasks_head->next;

			it->cur_tasks_head = it->dying_tasks_head;

		}

		if (it->task_pos == it->dying_tasks_head)

			css_task_iter_advance_css_set(it);

	} else {
@@ -4485,11 +4493,12 @@ repeat: 
			goto repeat;



		/* and dying leaders w/o live member threads */

		if (!atomic_read(&task->signal->live))

		if (it->cur_tasks_head == it->dying_tasks_head &&

		    !atomic_read(&task->signal->live))

			goto repeat;

	} else {

		/* skip all dying ones */

		if (task->flags & PF_EXITING)

		if (it->cur_tasks_head == it->dying_tasks_head)

			goto repeat;

	}

}

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