Re: [PATCH v3] net/sched: sch_qfq: Fix race condition on qfq_aggregate

[Xiang Mei <xmei5@asu.edu>]

On Thu, Jul 10, 2025 at 02:29:04PM -0700, Cong Wang wrote:
> On Thu, Jul 10, 2025 at 03:09:42AM -0700, Xiang Mei wrote:
> > A race condition can occur when 'agg' is modified in qfq_change_agg
> > (called during qfq_enqueue) while other threads access it
> > concurrently. For example, qfq_dump_class may trigger a NULL
> > dereference, and qfq_delete_class may cause a use-after-free.
> > 
> > This patch addresses the issue by:
> > 
> > 1. Moved qfq_destroy_class into the critical section.
> > 
> > 2. Added sch_tree_lock protection to qfq_dump_class and
> > qfq_dump_class_stats.
> > 
> > Fixes: 462dbc9101ac ("pkt_sched: QFQ Plus: fair-queueing service at DRR cost")
> > Signed-off-by: Xiang Mei <xmei5@asu.edu>
> 
> Reviewed-by: Cong Wang <xiyou.wangcong@gmail.com>
> 
> I am looking forward to your net-next patch to make it towards RCU. :)
> 
> Thanks.

Thanks so much for your help. I’ve learned a lot from you and the Linux 
kernel community.

I'll work on deliever an better patch after triage the left crashes.