Re: WARNING: ODEBUG bug in tcindex_destroy_work (3)

[Cong Wang]

On Sat, Mar 21, 2020 at 3:19 AM Thomas Gleixner <tglx@xxxxxxxxxxxxx> wrote:
>
> syzbot <syzbot+46f513c3033d592409d2@xxxxxxxxxxxxxxxxxxxxxxxxx> writes:
> > syzbot has found a reproducer for the following crash on:
> >
> > HEAD commit:    74522e7b net: sched: set the hw_stats_type in pedit loop
> > git tree:       net-next
> > console output: https://syzkaller.appspot.com/x/log.txt?x=14c85173e00000
> > kernel config:  https://syzkaller.appspot.com/x/.config?x=b5acf5ac38a50651
> > dashboard link: https://syzkaller.appspot.com/bug?extid=46f513c3033d592409d2
> > compiler:       gcc (GCC) 9.0.0 20181231 (experimental)
> > syz repro:      https://syzkaller.appspot.com/x/repro.syz?x=17bfff65e00000
> >
> > IMPORTANT: if you fix the bug, please add the following tag to the commit:
> > Reported-by: syzbot+46f513c3033d592409d2@xxxxxxxxxxxxxxxxxxxxxxxxx
> >
> > ------------[ cut here ]------------
> > ODEBUG: free active (active state 0) object type: work_struct hint: tcindex_destroy_rexts_work+0x0/0x20 net/sched/cls_tcindex.c:143
> ...
> >  __debug_check_no_obj_freed lib/debugobjects.c:967 [inline]
> >  debug_check_no_obj_freed+0x2e1/0x445 lib/debugobjects.c:998
> >  kfree+0xf6/0x2b0 mm/slab.c:3756
> >  tcindex_destroy_work+0x2e/0x70 net/sched/cls_tcindex.c:231
>
> So this is:
>
>         kfree(p->perfect);
>
> Looking at the place which queues that work:
>
> tcindex_destroy()
>
>    if (p->perfect) {
>         if (tcf_exts_get_net(&r->exts))
>             tcf_queue_work(&r-rwork, tcindex_destroy_rexts_work);
>         else
>             __tcindex_destroy_rexts(r)
>    }
>
>    .....
>
>    tcf_queue_work(&p->rwork, tcindex_destroy_work);
>
> So obviously if tcindex_destroy_work() runs before
> tcindex_destroy_rexts_work() then the above happens.

We use an ordered workqueue for tc filters, so these two
works are executed in the same order as they are queued.

Thanks.