From: Alan Huang <mmpgouride@gmail.com>
To: Eric Dumazet <edumazet@google.com>
Cc: linux-kernel@vger.kernel.org, netdev@vger.kernel.org,
rcu@vger.kernel.org, "Paul E. McKenney" <paulmck@kernel.org>,
roman.gushchin@linux.dev
Subject: Re: Question about the barrier() in hlist_nulls_for_each_entry_rcu()
Date: Fri, 21 Jul 2023 03:59:33 +0800 [thread overview]
Message-ID: <E9CF24C7-3080-4720-B540-BAF03068336B@gmail.com> (raw)
In-Reply-To: <CANn89iKJWw7zUP-E_d=Yhaz=Qw0R3Ae7ULaGgrtsi1yf2pfpGg@mail.gmail.com>
> 2023年7月21日 03:22，Eric Dumazet <edumazet@google.com> 写道：
>
> On Thu, Jul 20, 2023 at 8:54 PM Alan Huang <mmpgouride@gmail.com> wrote:
>>
>> 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)?
>
> Make sure sparse is happy.
It caused a problem without barrier(), and the deprecated ACCESS_ONCE() didn’t help:
https://lore.kernel.org/all/519D19DA.50400@yandex-team.ru/
So, my real question is: With READ_ONCE(ptr->field), are there still some unusual cases where gcc
decides not to reload ptr->field?
>
> Do you have a patch for review ?
Possibly next month. :)
>
>
>>
>>
>> [1] https://lore.kernel.org/all/1369699930.3301.494.camel@edumazet-glaptop/
>>
>> Thanks,
>> Alan
next prev parent reply other threads:[~2023-07-20 20:00 UTC|newest]
Thread overview: 26+ messages / expand[flat|nested] mbox.gz Atom feed top
2023-07-20 18:53 Question about the barrier() in hlist_nulls_for_each_entry_rcu() Alan Huang
2023-07-20 19:22 ` Eric Dumazet
2023-07-20 19:59 ` Alan Huang [this message]
2023-07-20 21:11 ` Eric Dumazet
2023-07-21 14:31 ` Alan Huang
2023-07-21 14:47 ` Eric Dumazet
2023-07-21 15:21 ` Alan Huang
2023-07-21 12:54 ` Joel Fernandes
2023-07-21 14:27 ` Alan Huang
2023-07-21 15:21 ` Joel Fernandes
2023-07-21 15:54 ` Alan Huang
2023-07-21 16:00 ` Joel Fernandes
2023-07-21 15:59 ` David Laight
2023-07-21 17:14 ` Joel Fernandes
2023-07-21 20:08 ` Alan Huang
2023-07-21 20:40 ` Alan Huang
2023-07-21 21:25 ` Alan Huang
2023-07-22 13:32 ` Alan Huang
2023-07-22 14:06 ` David Laight
2023-07-22 15:00 ` Alan Huang
2023-07-31 20:09 ` Paul E. McKenney
2023-08-03 13:40 ` Alan Huang
2023-08-03 13:53 ` Paul E. McKenney
2023-08-03 14:39 ` David Laight
2023-07-21 11:51 ` David Laight
2023-07-21 15:55 ` Alan Huang
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=E9CF24C7-3080-4720-B540-BAF03068336B@gmail.com \
--to=mmpgouride@gmail.com \
--cc=edumazet@google.com \
--cc=linux-kernel@vger.kernel.org \
--cc=netdev@vger.kernel.org \
--cc=paulmck@kernel.org \
--cc=rcu@vger.kernel.org \
--cc=roman.gushchin@linux.dev \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox