netdev - Re: Question about the barrier() in hlist_nulls_for_each_entry

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Message-Id: <FA8E8B15-A0B4-4EE1-B01E-FB1532103E17@gmail.com>
Date: Fri, 21 Jul 2023 23:55:07 +0800
From: Alan Huang <mmpgouride@...il.com>
To: David Laight <David.Laight@...LAB.COM>
Cc: "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
 "netdev@...r.kernel.org" <netdev@...r.kernel.org>,
 "rcu@...r.kernel.org" <rcu@...r.kernel.org>,
 "Paul E. McKenney" <paulmck@...nel.org>,
 Eric Dumazet <edumazet@...gle.com>,
 "roman.gushchin@...ux.dev" <roman.gushchin@...ux.dev>
Subject: Re: Question about the barrier() in hlist_nulls_for_each_entry_rcu()

> 2023年7月21日 19:51，David Laight <David.Laight@...LAB.COM> 写道：
> 
> From: Alan Huang
>> Sent: 20 July 2023 19:54
>> 
>> I noticed a commit c87a124a5d5e(“net: force a reload of first item in hlist_nulls_for_each_entry_rcu”)
>> and a related discussion [1].
> 
> Hmmm... that was all about the retry loop in ipv4/udp.c
> 
> AFAICT that retry got deleted by ca065d0c.
> 
> That also changes the list from hlist_nulls_xxx to hlist_xxx.
> (I'm not sure of the difference)
> 
> This might be why we're seeing unexpected 'port unreachable' messages?
> 
> Quite why that has just started happening is another issue.
> Most of the UDP sockets we create aren't 'connected' so I don't
> believe they get moved between hash chains - just deleted.
> The deletion should leave the hash chain intact.

Thanks for the information! :)

> 
> David
> 
> -
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