Subject: Re: [PATCH v2] rcu: fix a race in hlist_nulls_for_each_entry_rcu macro

From: "Paul E. McKenney" <[email-masked]>
Date: Sun, 2 Jun 2013 20:48:13 -0700

On Sun, Jun 02, 2013 at 08:12:49PM -0700, Eric Dumazet wrote:
> On Sun, 2013-06-02 at 19:58 -0700, David Miller wrote:
> > From: Eric Dumazet <[email-masked]>
> > 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 <[email-masked]>
> > >> 
> > >> 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.

One reason for the longer-than-usual response delays is my current timezone,
IST.  ;-)  Back to PDT on the 10th.

							Thanx, Paul