netdev - Question about the barrier() in hlist_nulls_for_each_entry

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Date: Fri, 21 Jul 2023 02:53:53 +0800
From: Alan Huang <mmpgouride@...il.com>
To: linux-kernel@...r.kernel.org,
 netdev@...r.kernel.org,
 rcu@...r.kernel.org
Cc: "Paul E. McKenney" <paulmck@...nel.org>,
 Eric Dumazet <edumazet@...gle.com>,
 roman.gushchin@...ux.dev
Subject: Question about the barrier() in hlist_nulls_for_each_entry_rcu()

Hi,

I noticed a commit c87a124a5d5e(“net: force a reload of first item in hlist_nulls_for_each_entry_rcu”)
and a related discussion [1].

After reading the whole discussion, it seems like that ptr->field was cached by gcc even with the deprecated
ACCESS_ONCE(), so my question is:

	Is that a compiler bug? If so, has this bug been fixed today, ten years later? 

	What about READ_ONCE(ptr->field)?

[1] https://lore.kernel.org/all/1369699930.3301.494.camel@edumazet-glaptop/

Thanks,
Alan