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SubjectRe: INFO: rcu detected stall in wg_packet_tx_worker
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.

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