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Date:   Wed, 26 Feb 2020 16:42:38 -0400
From:   Jason Gunthorpe <jgg@ziepe.ca>
To:     syzbot <syzbot+55de90ab5f44172b0c90@syzkaller.appspotmail.com>
Cc:     chuck.lever@oracle.com, dledford@redhat.com, leon@kernel.org,
        linux-kernel@vger.kernel.org, linux-rdma@vger.kernel.org,
        netdev@vger.kernel.org, parav@mellanox.com,
        syzkaller-bugs@googlegroups.com, willy@infradead.org,
        Bernard Metzler <bmt@zurich.ibm.com>
Subject: Re: possible deadlock in cma_netdev_callback
Message-ID: <20200226204238.GC31668@ziepe.ca>
References: <000000000000153fac059f740693@google.com>
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On Tue, Feb 25, 2020 at 09:39:10PM -0800, syzbot wrote:
> Hello,
> 
> syzbot found the following crash on:
> 
> HEAD commit:    6132c1d9 net: core: devlink.c: Hold devlink->lock from the..
> git tree:       net
> console output: https://syzkaller.appspot.com/x/log.txt?x=16978909e00000
> kernel config:  https://syzkaller.appspot.com/x/.config?x=3b8906eb6a7d6028
> dashboard link: https://syzkaller.appspot.com/bug?extid=55de90ab5f44172b0c90
> compiler:       gcc (GCC) 9.0.0 20181231 (experimental)
> syz repro:      https://syzkaller.appspot.com/x/repro.syz?x=12808281e00000
> C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=134ca6fde00000
> 
> IMPORTANT: if you fix the bug, please add the following tag to the commit:
> Reported-by: syzbot+55de90ab5f44172b0c90@syzkaller.appspotmail.com
> 
> iwpm_register_pid: Unable to send a nlmsg (client = 2)
> infiniband syz1: RDMA CMA: cma_listen_on_dev, error -98
> netlink: 'syz-executor639': attribute type 1 has an invalid length.
> 8021q: adding VLAN 0 to HW filter on device bond1
> bond1: (slave gretap1): making interface the new active one
> ======================================================
> WARNING: possible circular locking dependency detected
> 5.6.0-rc2-syzkaller #0 Not tainted
> syz-executor639/9689 is trying to acquire lock:
> ffffffff8a5d2a60 (lock#3){+.+.}, at: cma_netdev_callback+0xc6/0x380 drivers/infiniband/core/cma.c:4605
> 
> but task is already holding lock:
> ffffffff8a74da00 (rtnl_mutex){+.+.}, at: rtnl_lock net/core/rtnetlink.c:72 [inline]
> ffffffff8a74da00 (rtnl_mutex){+.+.}, at: rtnetlink_rcv_msg+0x405/0xaf0 net/core/rtnetlink.c:5433
>

Bernard, this is a siw bug too, it is not allowed to get RTNL in
siw_create_listen() (though this is probably for silly reasons and
could be fixed)

It is not easy to get this into the lockdep, I'll send a different
patch too

Jason