netdev - Re: [Patch net] rtnetlink: use rwsem to protect rtnl_af

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Message-ID: <68687fbb-d433-0f7a-9a3b-59f497ce6563@gmail.com>
Date:   Sat, 8 May 2021 17:22:21 +0900
From:   Taehee Yoo <ap420073@...il.com>
To:     Cong Wang <xiyou.wangcong@...il.com>
Cc:     Linux Kernel Network Developers <netdev@...r.kernel.org>,
        Cong Wang <cong.wang@...edance.com>,
        syzbot <syzbot+7d941e89dd48bcf42573@...kaller.appspotmail.com>
Subject: Re: [Patch net] rtnetlink: use rwsem to protect rtnl_af_ops list

On 5/7/21 6:30 AM, Cong Wang wrote:
 > On Thu, May 6, 2021 at 5:26 AM Taehee Yoo <ap420073@...il.com> wrote:
 >>
 >> On 5/6/21 8:36 AM, Cong Wang wrote:
 >>   > From: Cong Wang <cong.wang@...edance.com>
 >>   >
 >>
 >> Hi Cong,
 >> Thank you so much for fixing it!
 >>
 >>   > We use RTNL lock and RCU read lock to protect the global
 >>   > list rtnl_af_ops, however, this forces the af_ops readers
 >>   > being in atomic context while iterating this list,
 >>   > particularly af_ops->set_link_af(). This was not a problem
 >>   > until we begin to take mutex lock down the path in
 >>   > __ipv6_dev_mc_dec().
 >>   >
 >>   > Convert RTNL+RCU to rwsemaphore, so that we can block on
 >>   > the reader side while still allowing parallel readers.
 >>   >
 >>   > Reported-and-tested-by:
 >> syzbot+7d941e89dd48bcf42573@...kaller.appspotmail.com
 >>   > Fixes: 63ed8de4be81 ("mld: add mc_lock for protecting per-interface
 >> mld data")
 >>   > Cc: Taehee Yoo <ap420073@...il.com>
 >>   > Signed-off-by: Cong Wang <cong.wang@...edance.com>
 >>
 >> I have been testing this patch and I found a warning
 >
 > Ah, good catch! I clearly missed that code path.
 >
 > Can you help test the attached patch? syzbot is happy with it at least,
 > my CI bot is down so I can't run selftests for now.
 >

Hi Cong,
I have tested the attached patch with the syzbot reproducer and my own 
reproducer.
I couldn't find any problems such as warnings and other splats.
Thanks a lot!
Taehee