Messages in this thread Patch in this message |  | | Date | Wed, 03 Dec 2025 16:52:15 -0000 | | From | "tip-bot2 for Peng Wang" <> | | Subject | [tip: sched/urgent] sched/fair: Clear ->h_load_next when unregistering a cgroup |
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The following commit has been merged into the sched/urgent branch of tip:
Commit-ID: f85fd15b0da76f08e2d5bb4179c54993f7e07853 Gitweb: https://git.kernel.org/tip/f85fd15b0da76f08e2d5bb4179c54993f7e07853 Author: Peng Wang <peng_wang@linux.alibaba.com> AuthorDate: Fri, 24 Oct 2025 15:23:16 +08:00 Committer: Ingo Molnar <mingo@kernel.org> CommitterDate: Wed, 03 Dec 2025 17:44:01 +01:00
sched/fair: Clear ->h_load_next when unregistering a cgroup
An invalid pointer dereference bug was reported on ARM64 CPUs, and has not yet been seen on x86. A partial oops looks like:
Call trace: update_cfs_rq_h_load+0x80/0xb0 wake_affine+0x158/0x168 select_task_rq_fair+0x364/0x3a8 try_to_wake_up+0x154/0x648 wake_up_q+0x68/0xd0 futex_wake_op+0x280/0x4c8 do_futex+0x198/0x1c0 __arm64_sys_futex+0x11c/0x198
See: https://lore.kernel.org/all/20251013071820.1531295-1-CruzZhao@linux.alibaba.com/
We found that the task_group corresponding to the problematic se is not in the parent task_group’s children list, indicating that h_load_next points to an invalid address. Consider the following cgroup and task hierarchy:
A / \ / \ B E / \ | / \ t2 C D | | t0 t1
Here follows a timing sequence that may be responsible for triggering the problem:
CPU X CPU Y CPU Z wakeup t0 set list A->B->C traverse A->B->C t0 exits destroy C wakeup t2 set list A->E wakeup t1 set list A->B->D traverse A->B->C panic
CPU Z sets ->h_load_next list to A->B->D, but due to weaker memory ordering on ARM64, Y may observe A->B before it sees B->D, then in this time window, it can traverse A->B->C and reach an invalid se.
We can avoid stale pointer accesses by clearing ->h_load_next when unregistering a cgroup.
Fixes: 685207963be9 ("sched: Move h_load calculation to task_h_load()") Suggested-by: Vincent Guittot <vincent.guittot@linaro.org> Co-developed-by: Cruz Zhao <CruzZhao@linux.alibaba.com> Signed-off-by: Cruz Zhao <CruzZhao@linux.alibaba.com> Signed-off-by: Peng Wang <peng_wang@linux.alibaba.com> Signed-off-by: Ingo Molnar <mingo@kernel.org> Reviewed-by: Vincent Guittot <vincent.guittot@linaro.org> Link: https://patch.msgid.link/bf93d41ff9f2da19ef2c1cfb505362e0b48c39de.1761290330.git.peng_wang@linux.alibaba.com --- kernel/sched/fair.c | 9 +++++++++ 1 file changed, 9 insertions(+)
diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c index 769d7b7..00a32c9 100644 --- a/kernel/sched/fair.c +++ b/kernel/sched/fair.c @@ -13687,6 +13687,8 @@ void unregister_fair_sched_group(struct task_group *tg) struct rq *rq = cpu_rq(cpu); if (se) { + struct cfs_rq *parent_cfs_rq = cfs_rq_of(se); + if (se->sched_delayed) { guard(rq_lock_irqsave)(rq); if (se->sched_delayed) { @@ -13696,6 +13698,13 @@ void unregister_fair_sched_group(struct task_group *tg) list_del_leaf_cfs_rq(cfs_rq); } remove_entity_load_avg(se); + + /* + * Clear parent's h_load_next if it points to the + * sched_entity being freed, to avoid stale pointer. + */ + if (READ_ONCE(parent_cfs_rq->h_load_next) == se) + WRITE_ONCE(parent_cfs_rq->h_load_next, NULL); } /*
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