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SubjectRe: rcu: Add might_sleep() check to synchronize_rcu()
On Fri, 23 Mar 2018, Steven Rostedt wrote:
> On Fri, 23 Mar 2018 22:33:29 +0100 (CET)
> [ 150.741223] [<ffffffff81290287>] synchronize_rcu+0x27/0x90
> [ 150.746908] [<ffffffff83588b35>] __l2tp_session_unhash+0x3d5/0x550
>
> Looks like __l2tp_session_unhash() is the real culprit here.

Yes. I reported that to netdev already.

> [ 150.753281] [<ffffffff8358891f>] ? __l2tp_session_unhash+0x1bf/0x550
> [ 150.759828] [<ffffffff8114596a>] ? __local_bh_enable_ip+0x6a/0xd0
> [ 150.766123] [<ffffffff8358ddb0>] ? l2tp_udp_encap_recv+0xd90/0xd90
> [ 150.772497] [<ffffffff83588e97>] l2tp_tunnel_closeall+0x1e7/0x3a0
> [ 150.778782] [<ffffffff835897be>] l2tp_tunnel_destruct+0x30e/0x5a0
> [ 150.785067] [<ffffffff8358965a>] ? l2tp_tunnel_destruct+0x1aa/0x5a0
> [ 150.791537] [<ffffffff835894b0>] ? l2tp_tunnel_del_work+0x460/0x460
> [ 150.797997] [<ffffffff82ee8053>] __sk_destruct+0x53/0x570
> [ 150.803588] [<ffffffff81293918>] rcu_process_callbacks+0x898/0x1300
> [ 150.810048] [<ffffffff812939f7>] ? rcu_process_callbacks+0x977/0x1300
> [ 150.816684] [<ffffffff82ee8000>] ? __sk_dst_check+0x240/0x240
> [ 150.822625] [<ffffffff838be5d6>] __do_softirq+0x206/0x951
> [ 150.828223] [<ffffffff81147315>] irq_exit+0x165/0x190
> [ 150.833557] [<ffffffff838bd1eb>] smp_apic_timer_interrupt+0x7b/0xa0
> [ 150.840018] [<ffffffff838b9470>] apic_timer_interrupt+0xa0/0xb0
> [ 150.846132] <EOI> [ 150.848166] [<ffffffff838b6756>] ? native_safe_halt+0x6/0x10
> [ 150.854036] [<ffffffff8123bf2d>] ? trace_hardirqs_on+0xd/0x10
> [ 150.859973] [<ffffffff838b5d85>] default_idle+0x55/0x360
> [ 150.865478] [<ffffffff8106be0a>] arch_cpu_idle+0xa/0x10
>
> I think you want this instead, as __l2tp_session_unhash is what looks
> like might be hiding the call to synchronize_rcu(). It's not called in
> all instances, and I don't think your patch would have triggered the
> issues before hand. You want this:
>
> diff --git a/net/l2tp/l2tp_core.c b/net/l2tp/l2tp_core.c
> index 194a7483bb93..857b494bee29 100644
> --- a/net/l2tp/l2tp_core.c
> +++ b/net/l2tp/l2tp_core.c
> @@ -1677,6 +1677,8 @@ void __l2tp_session_unhash(struct l2tp_session *session)
> {
> struct l2tp_tunnel *tunnel = session->tunnel;
>
> + might_sleep();
> +
> /* Remove the session from core hashes */
> if (tunnel) {
> /* Remove from the per-tunnel hash */

That too :)

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