netdev - Re: [Patch net] smc: use RCU version of lower netdev searching

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Message-ID: <e0842025-5e21-4755-8e60-1832e9cfe672@linux.alibaba.com>
Date: Sat, 14 Sep 2024 10:28:15 +0800
From: "D. Wythe" <alibuda@...ux.alibaba.com>
To: Cong Wang <xiyou.wangcong@...il.com>
Cc: netdev@...r.kernel.org, Cong Wang <cong.wang@...edance.com>,
 syzbot+c75d1de73d3b8b76272f@...kaller.appspotmail.com,
 Wenjia Zhang <wenjia@...ux.ibm.com>, Jan Karcher <jaka@...ux.ibm.com>,
 Tony Lu <tonylu@...ux.alibaba.com>, Wen Gu <guwen@...ux.alibaba.com>
Subject: Re: [Patch net] smc: use RCU version of lower netdev searching

On 9/14/24 8:53 AM, Cong Wang wrote:
> On Thu, Sep 12, 2024 at 02:20:47PM +0800, D. Wythe wrote:
>>
>>
>> On 9/12/24 8:04 AM, Cong Wang wrote:
>>> From: Cong Wang <cong.wang@...edance.com>
>>>
>>> Both netdev_walk_all_lower_dev() and netdev_lower_get_next() have a
>>> RCU version, which are netdev_walk_all_lower_dev_rcu() and
>>> netdev_next_lower_dev_rcu(). Switching to the RCU version would
>>> eliminate the need for RTL lock, thus could amend the deadlock
>>> complaints from syzbot. And it could also potentially speed up its
>>> callers like smc_connect().
>>>
>>> Reported-by: syzbot+c75d1de73d3b8b76272f@...kaller.appspotmail.com
>>> Closes: https://syzkaller.appspot.com/bug?extid=c75d1de73d3b8b76272f
>>> Cc: Wenjia Zhang <wenjia@...ux.ibm.com>
>>> Cc: Jan Karcher <jaka@...ux.ibm.com>
>>> Cc: "D. Wythe" <alibuda@...ux.alibaba.com>
>>> Cc: Tony Lu <tonylu@...ux.alibaba.com>
>>> Cc: Wen Gu <guwen@...ux.alibaba.com>
>>> Signed-off-by: Cong Wang <cong.wang@...edance.com>
>>
>>
>> Haven't looked at your code yet, but the issue you fixed doesn't exist.
>> The real reason is that we lacks some lockdep annotations for
>> IPPROTO_SMC.
> 
> If you look at the code, it is not about sock lock annotations, it is
> about RTNL lock which of course has annotations.
> 

If so, please explain the deadlock issue mentioned in sysbot and
how it triggers deadlocks.

> And you don't even need to bother sock lock annotations for this specific
> case at all (I can't say any other case).
> 
> Thanks.