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Date: Tue, 14 Mar 2017 09:41:22 -0700 From: Cong Wang <xiyou.wangcong@...il.com> To: Eric Dumazet <edumazet@...gle.com> Cc: Dmitry Vyukov <dvyukov@...gle.com>, Eric Dumazet <eric.dumazet@...il.com>, David Miller <davem@...emloft.net>, Alexey Kuznetsov <kuznet@....inr.ac.ru>, James Morris <jmorris@...ei.org>, Hideaki YOSHIFUJI <yoshfuji@...ux-ipv6.org>, Patrick McHardy <kaber@...sh.net>, netdev <netdev@...r.kernel.org>, LKML <linux-kernel@...r.kernel.org>, Jamal Hadi Salim <jhs@...atatu.com>, syzkaller <syzkaller@...glegroups.com> Subject: Re: net: deadlock between ip_expire/sch_direct_xmit On Tue, Mar 14, 2017 at 7:56 AM, Eric Dumazet <edumazet@...gle.com> wrote: > On Tue, Mar 14, 2017 at 7:46 AM, Dmitry Vyukov <dvyukov@...gle.com> wrote: > >> I am confused. Lockdep has observed both of these stacks: >> >> CPU0 CPU1 >> ---- ---- >> lock(&(&q->lock)->rlock); >> lock(_xmit_ETHER#2); >> lock(&(&q->lock)->rlock); >> lock(_xmit_ETHER#2); >> >> >> So it somehow happened. Or what do you mean? >> > > Lockdep said " possible circular locking dependency detected " . > It is not an actual deadlock, but lockdep machinery firing. > > For a dead lock to happen, this would require that he ICMP message > sent by ip_expire() is itself fragmented and reassembled. > This cannot be, because ICMP messages are not candidates for > fragmentation, but lockdep can not know that of course... It doesn't have to be ICMP, as long as get the same hash for the inet_frag_queue, we will need to take the same lock and deadlock will happen. hash = ipqhashfn(iph->id, iph->saddr, iph->daddr, iph->protocol); So it is really up to this hash function.
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