Messages in this thread Patch in this message | | | From | Sargun Dhillon <> | Date | Wed, 9 Jan 2019 14:42:27 -0800 | Subject | Re: Crash in list_add_leaf_cfs_rq due to bad tmp_alone_branch |
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On Wed, Jan 9, 2019 at 2:14 PM Sargun Dhillon <sargun@sargun.me> wrote: > > I picked up c40f7d74c741a907cfaeb73a7697081881c497d0 sched/fair: Fix > infinite loop in update_blocked_averages() by reverting a9e7f6544b9c > and put it on top of 4.19.13. In addition to this, I uninlined > list_add_leaf_cfs_rq for debugging. > > This revealed a new bug that we didn't get to because we kept getting > crashes from the previous issue. When we are running with cgroups that > are rapidly changing, with CFS bandwidth control, and in addition > using the cpusets cgroup, we see this crash. Specifically, it seems to > occur with cgroups that are throttled and we change the allowed > cpuset. >
This patch from Gabriel should fix the problem:
[PATCH] sched/fair: Reset tmp_alone_branch on cfs_rq delete
When a child cfs_rq is added to the leaf cfs_rq list before its parent tmp_alone_branch is set to point to the child in preparation for the parent being added.
If the child is deleted before the parent is added then tmp_alone_branch points to a freed cfs_rq. Any future reference to tmp_alone_branch will result in a use after free.
Signed-off-by: Gabriel Hartmann <gabriel.hartmann@gmail.com> Reported-by: Sargun Dhillon <sargun@sargun.me> --- kernel/sched/fair.c | 5 +++++ 1 file changed, 5 insertions(+)
diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c index 7137bc343b4a..0987629cbb76 100644 --- a/kernel/sched/fair.c +++ b/kernel/sched/fair.c @@ -347,6 +347,11 @@ static inline void list_add_leaf_cfs_rq(struct cfs_rq *cfs_rq) static inline void list_del_leaf_cfs_rq(struct cfs_rq *cfs_rq) { if (cfs_rq->on_list) { + struct rq *rq = rq_of(cfs_rq); + + if (rq->tmp_alone_branch == &cfs_rq->leaf_cfs_rq_list) + rq->tmp_alone_branch = &rq->leaf_cfs_rq_list; + list_del_rcu(&cfs_rq->leaf_cfs_rq_list); cfs_rq->on_list = 0; }
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