netdev - BUG: held lock freed! - request_sock_queue::rskq

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Message-ID: <CAOi1vP9b78Y7-ddcZna2xM+vST6iuw+RmRL+BxR3HQZKbaa0ZA@mail.gmail.com>
Date:	Thu, 11 Feb 2016 23:43:34 +0100
From:	Ilya Dryomov <idryomov@...il.com>
To:	Eric Dumazet <edumazet@...gle.com>
Cc:	netdev <netdev@...r.kernel.org>,
	"David S. Miller" <davem@...emloft.net>,
	Ceph Development <ceph-devel@...r.kernel.org>
Subject: BUG: held lock freed! - request_sock_queue::rskq_lock

Hi Eric,

I'm hitting the following splat (attached in full):

kernel: =========================
kernel: [ BUG: held lock freed! ]
kernel: 4.5.0-rc1-ceph-00026-g5e0a311 #1 Not tainted
kernel: -------------------------
kernel: swapper/5/0 is freeing memory
ffff880035c9d200-ffff880035c9dbff, with a lock still held there!
kernel: (&(&queue->rskq_lock)->rlock){+.-...}, at:
[<ffffffff816f6a88>] inet_csk_reqsk_queue_add+0x28/0xa0
kernel: 4 locks held by swapper/5/0:
kernel: #0:  (rcu_read_lock){......}, at: [<ffffffff8169ef6b>]
netif_receive_skb_internal+0x4b/0x1f0
kernel: #1:  (rcu_read_lock){......}, at: [<ffffffff816e977f>]
ip_local_deliver_finish+0x3f/0x380
kernel: #2:  (slock-AF_INET){+.-...}, at: [<ffffffff81685ffb>]
sk_clone_lock+0x19b/0x440
kernel: #3:  (&(&queue->rskq_lock)->rlock){+.-...}, at:
[<ffffffff816f6a88>] inet_csk_reqsk_queue_add+0x28/0xa0

The first couple of occurrences were on 4.4-rc2, a couple of recent ones
on 4.5-rc1.  I'm suspecting your ebb516af60e1 ("tcp/dccp: fix race at
listener dismantle phase") and/or a bunch of related commits before it,
authored in the first half of Oct 2015.

The spinlock that lockdep complains about is embedded in
inet_connection_sock, which I think is getting freed in
inet_child_forget(), called from inet_csk_reqsk_queue_add():

inet_csk_complete_hashdance
  inet_csk_reqsk_queue_add
    spin_lock(&queue->rskq_lock)
    inet_child_forget
      reqsk_put
        reqsk_free
          sock_put(req->rsk_listener)
          # rsk_listener is sk that queue is embedded in #

Your comment in inet_csk_complete_hashdance()

                /* Warning: caller must not call reqsk_put(req);
                 * child stole last reference on it.
                 */

suggests that there is only one reference to req at that point in time
and yet ebb516af60e1 added a reqsk_put() to that path: there was one in
inet_csk_listen_stop() before, but not in inet_csk_reqsk_queue_add().

This is from a quick and dirty git blame analysis, so don't shout if
all of it is wrong...

Thanks,

                Ilya

View attachment "rskq_lock.txt" of type "text/plain" (5867 bytes)