netdev - WARN_ON in commit 0ffdaf5 "net/sock: add WARN_ON(parent->sk) in sock

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Date:   Fri, 4 Aug 2017 19:13:18 +0800
From:   Guoqing Jiang <gqjiang@...e.com>
To:     sowmini.varadhan@...cle.com, davem@...emloft.net
Cc:     netdev@...r.kernel.org, Guoqing Jiang <gqjiang@...e.com>
Subject: WARN_ON in commit 0ffdaf5 "net/sock: add WARN_ON(parent->sk) in
 sock_graft()"

HI,

With commit 0ffdaf5b41cf4435ece14d1d3e977ce69012a20d "net/sock: add 
WARN_ON(parent->sk) in sock_graft()",
I can see the WARN_ON is triggered easily by dlm subsystem.

tcp_accept_from_sock() in  fs/dlm/lowcomms.c has the following snippet:

1.    result = sock_create_kern(&init_net, dlm_local_addr[0]->ss_family,
                                       SOCK_STREAM, IPPROTO_TCP, &newsock);
         sk is set by the path "sock_create_kern -> __sock_creat -> 
pf->create => inet_create -> sock_init_data"
     ...
2.    result = con->sock->ops->accept(con->sock, newsock, O_NONBLOCK, true);
         Then sock_graft is called by "con->sock->ops->accept => 
inet_accept -> sock_graft "

Does it mean call accept() after the just created socket is not a 
acceptable behavior? Any comment will be appreciate, thanks.

Regards,
Guoqing