Date: Wed, 15 Mar 2017 07:30:19 -0400
From: Sowmini Varadhan <sowmini.varadhan@oracle.com>
To: Dmitry Vyukov <dvyukov@google.com>
Cc: Herbert Xu <herbert@gondor.apana.org.au>,
        David Miller <davem@davemloft.net>, linux-crypto@vger.kernel.org,
        LKML <linux-kernel@vger.kernel.org>,
        Eric Dumazet <edumazet@google.com>,
        Cong Wang <xiyou.wangcong@gmail.com>, netdev <netdev@vger.kernel.org>,
        santosh.shilimkar@oracle.com, rds-devel@oss.oracle.com,
        syzkaller <syzkaller@googlegroups.com>
Subject: Re: crypto: deadlock between crypto_alg_sem/rtnl_mutex/genl_mutex
Message-ID: <20170315113019.GA28050@oracle.com>
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On (03/15/17 10:08), Dmitry Vyukov wrote:
> After I've applied the patch these reports stopped to happen, and I
> have not seem any other reports that look relevant.
> However, it there was one, but it looks like a different issue and it
> was probably masked by massive amounts of original deadlock reports:

Yes, this looks like a valid deadlock.

I think there may be some ->dumpit callbacks that take the rtnl_lock
and do not unlock it before return, e.g., I see nl80211_dump_interface()
doing this at 

   2612         rtnl_lock();
   2613         if (!cb->args[2]) {
     :
   2619                 ret = nl80211_dump_wiphy_parse(skb, cb, &state);
   2620                 if (ret)
   2621                         return ret;

afaict, nl80211_dump_wiphy_parse does not itself do rtnl_unlock on error.


If that's the case then we'd run into the circular locking dependancy
flagged by lockdep. 

Disclaimer: I did not check every single ->dumpit, there may be more
than one of these..