netdev - Re: [PATCH]ipv6: multicast: In mld_send_cr function moving read lock to second for loop

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Message-Id: <20180818.135819.1279366350823380240.davem@davemloft.net>
Date:   Sat, 18 Aug 2018 13:58:19 -0700 (PDT)
From:   David Miller <davem@...emloft.net>
To:     guru2018@...il.com
Cc:     netdev@...r.kernel.org, kuznet@....inr.ac.ru,
        yoshfuji@...ux-ipv6.org
Subject: Re: [PATCH]ipv6: multicast: In mld_send_cr function moving read
 lock to second for loop

From: Guruswamy Basavaiah <guru2018@...il.com>
Date: Fri, 17 Aug 2018 18:01:41 +0530

> @@ -1860,7 +1860,6 @@ static void mld_send_cr(struct inet6_dev *idev)
>      struct sk_buff *skb = NULL;
>      int type, dtype;
> 
> -    read_lock_bh(&idev->lock);
>      spin_lock(&idev->mc_lock);
> 
>      /* deleted MCA's */

This will lead to deadlocks, idev->mc_lock must be taken with _bh().

I have zero confidence in this change, did you do any stress testing
with lockdep enabled?  It would have caught this quickly.