linux-kernel - Re: [PATCH v2 9/9] netfilter: Replace smp_read_barrier_depends() with lockless

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <1416614703.20938.0.camel@edumazet-glaptop2.roam.corp.google.com>
Date:	Fri, 21 Nov 2014 16:05:03 -0800
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	Pranith Kumar <bobby.prani@...il.com>
Cc:	Pablo Neira Ayuso <pablo@...filter.org>,
	Patrick McHardy <kaber@...sh.net>,
	Jozsef Kadlecsik <kadlec@...ckhole.kfki.hu>,
	"David S. Miller" <davem@...emloft.net>,
	Alexey Kuznetsov <kuznet@....inr.ac.ru>,
	James Morris <jmorris@...ei.org>,
	Hideaki YOSHIFUJI <yoshfuji@...ux-ipv6.org>,
	netfilter-devel@...r.kernel.org, coreteam@...filter.org,
	"open list:NETWORKING [IPv4/..." <netdev@...r.kernel.org>,
	open list <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v2 9/9] netfilter: Replace smp_read_barrier_depends()
 with lockless_dereference()


On Fri, 2014-11-21 at 16:57 -0500, Pranith Kumar wrote:

> Hi Eric,
> 
> Thanks for looking at this patch.
> 
> I've been scratching my head since morning trying to find out what was
> so obviously wrong with this patch. Alas, I don't see what you do.
> 
> Could you point it out and show me how incompetent I am, please?
> 
> Thanks!

Well, even it the code is _not_ broken, I don't see any value with this
patch.

If I use git blame on current code, line containing
smp_read_barrier_depends() exactly points to the relevant commit [1]

After your change, it will point to some cleanup, which makes little
sense to me, considering you did not change the smp_wmb() in
xt_replace_table().

I, as a netfilter contributor would like to keep current code as is,
because it is how I feel safe with it.

We have a proliferation of interfaces, but this does not help to
understand the issues and code maintenance.

smp_read_barrier_depends() better documents the read barrier than 
lockless_dereference().

The point of having a lock or not is irrelevant here.

[1]
http://git.kernel.org/cgit/linux/kernel/git/davem/net.git/commit/?id=b416c144f46af1a30ddfa4e4319a8f077381ad63




--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/