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

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Message-ID: <ZuTehlEoyi4PPmQA@pop-os.localdomain>
Date: Fri, 13 Sep 2024 17:53:26 -0700
From: Cong Wang <xiyou.wangcong@...il.com>
To: "D. Wythe" <alibuda@...ux.alibaba.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 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.

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.