From: Tejun Heo tj@kernel.org
commit cee0c33c546a93957a52ae9ab6bebadbee765ec5 upstream.
b636fd38dc40 ("cgroup: Implement css_task_iter_skip()") introduced css_task_iter_skip() which is used to fix task iterations skipping dying threadgroup leaders with live threads. Skipping is implemented as a subportion of full advancing but css_task_iter_next() forgot to fully advance a skipped iterator before determining the next task to visit causing it to return invalid task pointers.
Fix it by making css_task_iter_next() fully advance the iterator if it has been skipped since the previous iteration.
Signed-off-by: Tejun Heo tj@kernel.org Reported-by: syzbot Link: http://lkml.kernel.org/r/00000000000097025d058a7fd785@google.com Fixes: b636fd38dc40 ("cgroup: Implement css_task_iter_skip()") Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org
--- kernel/cgroup/cgroup.c | 4 ++++ 1 file changed, 4 insertions(+)
--- a/kernel/cgroup/cgroup.c +++ b/kernel/cgroup/cgroup.c @@ -4197,6 +4197,10 @@ struct task_struct *css_task_iter_next(s
spin_lock_irq(&css_set_lock);
+ /* @it may be half-advanced by skips, finish advancing */ + if (it->flags & CSS_TASK_ITER_SKIPPED) + css_task_iter_advance(it); + if (it->task_pos) { it->cur_task = list_entry(it->task_pos, struct task_struct, cg_list);