lkml.org 
[lkml]   [2020]   [Mar]   [23]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
From
SubjectRe: WARNING: ODEBUG bug in tcindex_destroy_work (3)
Date
Cong Wang <xiyou.wangcong@gmail.com> writes:
> On Sat, Mar 21, 2020 at 3:19 AM Thomas Gleixner <tglx@linutronix.de> wrote:
>> > ------------[ 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.

The workqueue is ordered, but look how the work is queued on the work
queue:

tcf_queue_work()
queue_rcu_work()
call_rcu(&rwork->rcu, rcu_work_rcufn);

So after the grace period elapses rcu_work_rcufn() queues it in the
actual work queue.

Now tcindex_destroy() is invoked via tcf_proto_destroy() which can be
invoked from preemtible context. Now assume the following:

CPU0
tcf_queue_work()
tcf_queue_work(&r->rwork, tcindex_destroy_rexts_work);

-> Migration

CPU1
tcf_queue_work(&p->rwork, tcindex_destroy_work);

So your RCU callbacks can be placed on different CPUs which obviously
has no ordering guarantee at all. See also:

https://mirrors.edge.kernel.org/pub/linux/kernel/people/paulmck/Answers/RCU/RCUCBordering.html

Disabling preemption would "fix" it today, but that documentation
explicitely says that it is an implementation detail, but not
guaranteed by design.

Thanks,

tglx

\
 
 \ /
  Last update: 2020-03-23 22:14    [W:0.130 / U:21.792 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site