On Fri, Jan 24, 2020 at 3:40 AM Michal Koutný <mkoutny@xxxxxxxx> wrote: > > 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 c03cd7738a83 ("cgroup: Include dying > leaders with live threads in PROCS iterations") but it may be reviewed > later. > > Reported-by: Suren Baghdasaryan <surenb@xxxxxxxxxx> > Fixes: c03cd7738a83 ("cgroup: Include dying leaders with live threads in PROCS iterations") > Signed-off-by: Michal Koutný <mkoutny@xxxxxxxx> > --- > include/linux/cgroup.h | 1 + > kernel/cgroup/cgroup.c | 23 ++++++++++++++++------- > 2 files changed, 17 insertions(+), 7 deletions(-) > > diff --git a/include/linux/cgroup.h b/include/linux/cgroup.h > index d7ddebd0cdec..e75d2191226b 100644 > --- a/include/linux/cgroup.h > +++ b/include/linux/cgroup.h > @@ -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; > diff --git a/kernel/cgroup/cgroup.c b/kernel/cgroup/cgroup.c > index 735af8f15f95..a6e3619e013b 100644 > --- a/kernel/cgroup/cgroup.c > +++ b/kernel/cgroup/cgroup.c > @@ -4404,12 +4404,16 @@ 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; > @@ -4467,10 +4471,14 @@ static void css_task_iter_advance(struct css_task_iter *it) > 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 { > @@ -4489,11 +4497,12 @@ static void css_task_iter_advance(struct css_task_iter *it) > 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; > } > } > -- > 2.24.1 > Tested-by: Suren Baghdasaryan <surenb@xxxxxxxxxx> Thanks!