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

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
...@@ -62,6 +62,7 @@ struct css_task_iter { ...@@ -62,6 +62,7 @@ struct css_task_iter {
struct list_head *mg_tasks_head; struct list_head *mg_tasks_head;
struct list_head *dying_tasks_head; struct list_head *dying_tasks_head;
struct list_head *cur_tasks_head;
struct css_set *cur_cset; struct css_set *cur_cset;
struct css_set *cur_dcset; struct css_set *cur_dcset;
struct task_struct *cur_task; struct task_struct *cur_task;
......
...@@ -4400,12 +4400,16 @@ static void css_task_iter_advance_css_set(struct css_task_iter *it) ...@@ -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)); } 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; 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; it->task_pos = cset->mg_tasks.next;
else it->cur_tasks_head = &cset->mg_tasks;
} else {
it->task_pos = cset->dying_tasks.next; it->task_pos = cset->dying_tasks.next;
it->cur_tasks_head = &cset->dying_tasks;
}
it->tasks_head = &cset->tasks; it->tasks_head = &cset->tasks;
it->mg_tasks_head = &cset->mg_tasks; it->mg_tasks_head = &cset->mg_tasks;
...@@ -4463,10 +4467,14 @@ static void css_task_iter_advance(struct css_task_iter *it) ...@@ -4463,10 +4467,14 @@ static void css_task_iter_advance(struct css_task_iter *it)
else else
it->task_pos = it->task_pos->next; 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; 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->task_pos = it->dying_tasks_head->next;
it->cur_tasks_head = it->dying_tasks_head;
}
if (it->task_pos == it->dying_tasks_head) if (it->task_pos == it->dying_tasks_head)
css_task_iter_advance_css_set(it); css_task_iter_advance_css_set(it);
} else { } else {
...@@ -4485,11 +4493,12 @@ static void css_task_iter_advance(struct css_task_iter *it) ...@@ -4485,11 +4493,12 @@ static void css_task_iter_advance(struct css_task_iter *it)
goto repeat; goto repeat;
/* and dying leaders w/o live member threads */ /* 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; goto repeat;
} else { } else {
/* skip all dying ones */ /* skip all dying ones */
if (task->flags & PF_EXITING) if (it->cur_tasks_head == it->dying_tasks_head)
goto repeat; goto repeat;
} }
} }
......
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