linux-next: zillions of lockdep whinges in include/net/sock.h:1408

[Valdis Kletnieks <Valdis.Kletnieks@vt.edu>]

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linux-next 20160420 is whining at an incredible rate - in 20 minutes of
uptime, I piled up some 41,000 hits from all over the place (cleaned up
to skip the CPU and PID so the list isn't quite so long):

% grep include/net/sock.h /var/log/messages | cut -f5- -d: |  sed -e 's/PID: [0-9]* /PID: (elided) /' -e 's/CPU: [0-3]/CPU: +/' | sort | uniq -c | sort -nr
  13468  CPU: + PID: (elided) at include/net/sock.h:1408 tcp_v6_rcv+0xc20/0xcb0
   9770  CPU: + PID: (elided) at include/net/sock.h:1408 udp_queue_rcv_skb+0x3ca/0x6d0
   7706  CPU: + PID: (elided) at include/net/sock.h:1408 sock_owned_by_user+0x91/0xa0
   2818  CPU: + PID: (elided) at include/net/sock.h:1408 udpv6_queue_rcv_skb+0x3b6/0x6d0
   1981  CPU: + PID: (elided) at include/net/sock.h:1408 tcp_write_timer+0xf2/0x110
   1954  CPU: + PID: (elided) at include/net/sock.h:1408 tcp_delack_timer+0x110/0x130
   1912  CPU: + PID: (elided) at include/net/sock.h:1408 tcp_keepalive_timer+0x136/0x2c0
    882  CPU: + PID: (elided) at include/net/sock.h:1408 tcp_close+0x226/0x4f0
    804  CPU: + PID: (elided) at include/net/sock.h:1408 tcp_tasklet_func+0x192/0x1e0
     28  CPU: + PID: (elided) at include/net/sock.h:1408 tcp_child_process+0x17a/0x350
      2  CPU: + PID: (elided) at include/net/sock.h:1408 tcp_v6_err+0x401/0x660
      2  CPU: + PID: (elided) at include/net/sock.h:1408 tcp_v6_err+0x1fd/0x660

Seems to be from this commit, which is apparently over-stringent or
isn't handling some case correctly:

commit fafc4e1ea1a4c1eb13a30c9426fb799f5efacbc3
Author: Hannes Frederic Sowa <hannes@stressinduktion.org>
Date:   Fri Apr 8 15:11:27 2016 +0200

    sock: tigthen lockdep checks for sock_owned_by_user

    sock_owned_by_user should not be used without socket lock held. It seems
    to be a common practice to check .owned before lock reclassification, so
    provide a little help to abstract this check away.

    Cc: linux-cifs@vger.kernel.org
    Cc: linux-bluetooth@vger.kernel.org
    Cc: linux-nfs@vger.kernel.org
    Signed-off-by: Hannes Frederic Sowa <hannes@stressinduktion.org>
    Signed-off-by: David S. Miller <davem@davemloft.net>


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