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cgroup: Iterate tasks that did not finish do_exit()

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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 c03cd7738a ("cgroup: Include dying
leaders with live threads in PROCS iterations") but it may be reviewed
later.

Reported-by: Suren Baghdasaryan <surenb@google.com>
Fixes: c03cd7738a ("cgroup: Include dying leaders with live threads in PROCS iterations")
Signed-off-by: Michal Koutný <mkoutny@suse.com>
Signed-off-by: Tejun Heo <tj@kernel.org>
This commit is contained in:
Michal Koutný 2020-01-24 12:40:15 +01:00 committed by Tejun Heo
parent 2d4ecb030d
commit 9c974c7724
2 changed files with 17 additions and 7 deletions
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1
include/linux/cgroup.h
View File

@ -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;

23
kernel/cgroup/cgroup.c
View File

@ -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;
}
}