netdev - Re: Crash due to mutex genl_lock called from RCU context

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Date:   Sat, 26 Nov 2016 22:28:21 -0800
From:   Cong Wang <xiyou.wangcong@...il.com>
To:     Eric Dumazet <eric.dumazet@...il.com>
Cc:     Subash Abhinov Kasiviswanathan <subashab@...eaurora.org>,
        Thomas Graf <tgraf@...g.ch>,
        Linux Kernel Network Developers <netdev@...r.kernel.org>
Subject: Re: Crash due to mutex genl_lock called from RCU context

On Sat, Nov 26, 2016 at 6:26 PM, Eric Dumazet <eric.dumazet@...il.com> wrote:
>
> Are you telling me inet_release() is called when we close() the first
> file descriptor ?
>
> fd1 = socket()
> fd2 = dup(fd1);
> close(fd2) -> release() ???

Sorry, I didn't express myself clearly, I meant your change,
if exclude the SOCK_RCU_FREE part, basically reverts this commit:

commit 3f660d66dfbc13ea4b61d3865851b348444c24b4
Author: Herbert Xu <herbert@...dor.apana.org.au>
Date:   Thu May 3 03:17:14 2007 -0700

    [NETLINK]: Kill CB only when socket is unused

IOW, ->release() is called when the last sock fd ref is gone, but ->destructor()
is called with the last sock ref is gone. They are very different.


>> I don't see why we need to get genl_lock in ->done() here, because we are
>> already the last sock using it and module ref protects the ops from being
>> removed via module, seems we are pretty safe without any lock.
>
> Well, at least this exposes a real bug in Thomas patch.
>
> Removing the lock might be done for net-next, not stable branches.

I am confused, what Subash reported is a kernel warning which can
surely be fixed by removing genl lock (if it is correct, I need to double
check), so why for net-next?