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

[Cong Wang <xiyou.wangcong@gmail.com>]

On Sat, Sep 14, 2024 at 10:28:15AM +0800, D. Wythe wrote:
> 
> 
> 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@bytedance.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@syzkaller.appspotmail.com
> > > > Closes: https://syzkaller.appspot.com/bug?extid=c75d1de73d3b8b76272f
> > > > Cc: Wenjia Zhang <wenjia@linux.ibm.com>
> > > > Cc: Jan Karcher <jaka@linux.ibm.com>
> > > > Cc: "D. Wythe" <alibuda@linux.alibaba.com>
> > > > Cc: Tony Lu <tonylu@linux.alibaba.com>
> > > > Cc: Wen Gu <guwen@linux.alibaba.com>
> > > > Signed-off-by: Cong Wang <cong.wang@bytedance.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.

Sure, but what questions do you have here? To me, the lockdep output is
self-explained. Please kindly let me know if you have any troubles
understanding it, I am always happy to help.

Thanks.