linux-kernel - Re: [PATCH v2] rcu: fix a race in hlist_nulls_for_each_entry

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Message-ID: <20130603060557.GD29614@linux.vnet.ibm.com>
Date:	Sun, 2 Jun 2013 23:05:57 -0700
From:	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
To:	David Miller <davem@...emloft.net>
Cc:	eric.dumazet@...il.com, klamm@...dex-team.ru, brouer@...hat.com,
	dipankar@...ibm.com, zhmurov@...dex-team.ru,
	linux-kernel@...r.kernel.org, netdev@...r.kernel.org,
	kuznet@....inr.ac.ru, jmorris@...ei.org, yoshfuji@...ux-ipv6.org,
	kaber@...sh.net, David.Laight@...LAB.COM
Subject: Re: [PATCH v2] rcu: fix a race in hlist_nulls_for_each_entry_rcu
 macro

On Sun, Jun 02, 2013 at 08:49:15PM -0700, David Miller wrote:
> From: "Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
> Date: Sun, 2 Jun 2013 20:42:54 -0700
> 
> > On Sun, Jun 02, 2013 at 08:27:03PM -0700, David Miller wrote:
> >> From: Eric Dumazet <eric.dumazet@...il.com>
> >> Date: Sun, 02 Jun 2013 20:12:49 -0700
> >> 
> >> > On Sun, 2013-06-02 at 19:58 -0700, David Miller wrote:
> >> >> From: Eric Dumazet <eric.dumazet@...il.com>
> >> >> Date: Sun, 02 Jun 2013 16:31:35 -0700
> >> >> 
> >> >> > On Thu, 2013-05-30 at 12:25 +0400, Roman Gushchin wrote:
> >> >> >> On 29.05.2013 23:06, Eric Dumazet wrote:
> >> >> >> > On Wed, 2013-05-29 at 14:09 +0400, Roman Gushchin wrote:
> >> >> >> >
> >> >> >> > True, these lookup functions are usually structured the same around the
> >> >> >> > hlist_nulls_for_each_entry_rcu() loop.
> >> >> >> >
> >> >> >> > A barrier() right before the loop seems to be a benefit, the size of
> >> >> >> > assembly code is reduced by 48 bytes.
> >> >> >> >
> >> >> >> > And its one of the documented way to handle this kind of problems
> >> >> >> > (Documentation/atomic_ops.txt line 114)
> >> >> >> >
> >> >> >> > I guess we should amend this documentation, eventually.
> >> >> >> >
> >> >> >> > Thanks, please add you "Signed-off-by" if you agree with the patch.
> >> >> >> >
> >> >> >> 
> >> >> >> Signed-off-by: Roman Gushchin <klamm@...dex-team.ru>
> >> >> >> 
> >> >> >> Many thanks to you, Paul E. McKenney and David Laight for your
> >> >> >> patches, help and participation in this discussion.
> >> >> > 
> >> >> > Thanks to you !
> >> >> > 
> >> >> > David, is there any problem with the patch ?
> >> >> > 
> >> >> > http://patchwork.ozlabs.org/patch/247360/ says "Not applicable", please
> >> >> > tell me what is needed to get it merged.
> >> >> 
> >> >> It's not a networking patch, it's a patch for generic RCU upstream.
> >> >> So it either goes through Paul McKenney, or directly via Linus on
> >> >> linux-kernel.
> >> > 
> >> > Well, whole discussion went on linux kernel, and you were the original
> >> > committer of this patch five years ago.
> >> > 
> >> > http://git.kernel.org/cgit/linux/kernel/git/davem/net-next.git/commit/?id=bbaffaca4810de1a25e32ecaf836eeaacc7a3d11
> >> > 
> >> > So please Paul or David make sure the patch goes in.
> >> > 
> >> > My only concern is that Paul seems quite busy these days.
> >> 
> >> Ok I can take it then, no problem.
> > 
> > Or if you would like to take it:
> > 
> > Acked-by: Paul E. McKenney <paulmck@...ux.vnet.ibm.com>
> 
> Let's end this deadlock by me taking it :-)

You got it!  ;-)

							Thanx, Paul

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