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SubjectRe: INFO: rcu detected stall in wg_packet_tx_worker
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On 4/26/20 1:26 PM, Eric Dumazet wrote:
>
>
> On 4/26/20 12:42 PM, Jason A. Donenfeld wrote:
>> On Sun, Apr 26, 2020 at 1:40 PM Eric Dumazet <eric.dumazet@gmail.com> wrote:
>>>
>>>
>>>
>>> On 4/26/20 10:57 AM, syzbot wrote:
>>>> syzbot has bisected this bug to:
>>>>
>>>> commit e7096c131e5161fa3b8e52a650d7719d2857adfd
>>>> Author: Jason A. Donenfeld <Jason@zx2c4.com>
>>>> Date: Sun Dec 8 23:27:34 2019 +0000
>>>>
>>>> net: WireGuard secure network tunnel
>>>>
>>>> bisection log: https://syzkaller.appspot.com/x/bisect.txt?x=15258fcfe00000
>>>> start commit: b2768df2 Merge branch 'for-linus' of git://git.kernel.org/..
>>>> git tree: upstream
>>>> final crash: https://syzkaller.appspot.com/x/report.txt?x=17258fcfe00000
>>>> console output: https://syzkaller.appspot.com/x/log.txt?x=13258fcfe00000
>>>> kernel config: https://syzkaller.appspot.com/x/.config?x=b7a70e992f2f9b68
>>>> dashboard link: https://syzkaller.appspot.com/bug?extid=0251e883fe39e7a0cb0a
>>>> userspace arch: i386
>>>> syz repro: https://syzkaller.appspot.com/x/repro.syz?x=15f5f47fe00000
>>>> C reproducer: https://syzkaller.appspot.com/x/repro.c?x=11e8efb4100000
>>>>
>>>> Reported-by: syzbot+0251e883fe39e7a0cb0a@syzkaller.appspotmail.com
>>>> Fixes: e7096c131e51 ("net: WireGuard secure network tunnel")
>>>>
>>>> For information about bisection process see: https://goo.gl/tpsmEJ#bisection
>>>>
>>>
>>> I have not looked at the repro closely, but WireGuard has some workers
>>> that might loop forever, cond_resched() might help a bit.
>>
>> I'm working on this right now. Having a bit difficult of a time
>> getting it to reproduce locally...
>>
>> The reports show the stall happening always at:
>>
>> static struct sk_buff *
>> sfq_dequeue(struct Qdisc *sch)
>> {
>> struct sfq_sched_data *q = qdisc_priv(sch);
>> struct sk_buff *skb;
>> sfq_index a, next_a;
>> struct sfq_slot *slot;
>>
>> /* No active slots */
>> if (q->tail == NULL)
>> return NULL;
>>
>> next_slot:
>> a = q->tail->next;
>> slot = &q->slots[a];
>>
>> Which is kind of interesting, because it's not like that should block
>> or anything, unless there's some kasan faulting happening.
>>
>
> I am not really sure WireGuard is involved, the repro does not rely on it anyway.
>

Yes, do not spend too much time on this.

syzbot found its way into crazy qdisc settings these last days.

( I sent a patch yesterday for choke qdisc, it seems similar checks are needed in sfq )

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