From: "Paul E. McKenney" <paulmck@linux•vnet.ibm.com>
To: James Chapman <jchapman@katalix•com>
Cc: Stephen Hemminger <shemminger@vyatta•com>, netdev@vger•kernel.org
Subject: Re: [PATCH v3 10/12] l2tp: Add L2TP ethernet pseudowire support
Date: Fri, 2 Apr 2010 08:24:02 -0700 [thread overview]
Message-ID: <20100402152402.GA6017@linux.vnet.ibm.com> (raw)
In-Reply-To: <20100331173836.GG2461@linux.vnet.ibm.com>
On Wed, Mar 31, 2010 at 10:38:36AM -0700, Paul E. McKenney wrote:
> On Wed, Mar 31, 2010 at 10:35:29AM +0100, James Chapman wrote:
> > Stephen Hemminger wrote:
> > > On Tue, 30 Mar 2010 17:18:19 +0100
> > > James Chapman <jchapman@katalix•com> wrote:
> > >
> > >> +struct l2tp_eth_net {
> > >> + struct list_head l2tp_eth_dev_list;
> > >> + rwlock_t l2tp_eth_lock;
> > >> +};
> > >
> > > Reader/write locks are discouraged because they are slower than
> > > spin locks. If you have lots of readers use RCU, if reading
> > > is infrequent just use a spin lock.
> >
> > Ok. In doing the conversion of the rwlocks in l2tp_core.c, I'm finding
> > that some list access primitives don't have rcu equivalents, namely
> > list_is_last(), list_for_each_entry_safe(). Is this intentional? Should
> > I add the missing ones in a separate patch?
>
> The list_is_last() is RCU-safe already, since the ->next pointer is
> only compared, never dereferenced. I suggest adding a comment to its
> header stating that it is RCU-safe.
>
> Feel free to create a list_for_each_entry_safe_rcu(), and I will be
> happy to review it.
Right. When using RCU, list_for_each_entry_safe_rcu() is not needed,
because destruction of the element you removed doesn't happen until the
end of a subsequent grace period. By which time you will be done with
your RCU read-side critical section.
So you can just use list_for_each_entry_rcu(), you do not need a new
list_for_each_entry_safe_rcu().
But you did have me going for a bit!!! ;-)
Thanx, Paul
next prev parent reply other threads:[~2010-04-02 15:24 UTC|newest]
Thread overview: 32+ messages / expand[flat|nested] mbox.gz Atom feed top
2010-03-30 16:17 [PATCH v3 00/12] l2tp: Introduce L2TPv3 support James Chapman
2010-03-30 16:17 ` [PATCH v3 01/12] l2tp: Relocate pppol2tp driver to new net/l2tp directory James Chapman
2010-03-30 16:17 ` [PATCH v3 02/12] l2tp: Split pppol2tp patch into separate l2tp and ppp parts James Chapman
2010-03-30 16:17 ` [PATCH v3 03/12] ppp: Add ppp_dev_name() exported function James Chapman
2010-03-30 16:17 ` [PATCH v3 04/12] l2tp: Add ppp device name to L2TP ppp session data James Chapman
2010-03-30 16:29 ` Stephen Hemminger
2010-03-31 7:43 ` James Chapman
2010-03-31 8:46 ` David Miller
2010-03-31 23:08 ` Stephen Hemminger
2010-04-01 7:19 ` James Chapman
2010-04-01 7:30 ` Eric Dumazet
2010-04-01 8:55 ` James Chapman
2010-04-01 7:34 ` David Miller
2010-04-01 8:59 ` James Chapman
2010-04-01 9:04 ` David Miller
2010-03-30 16:17 ` [PATCH v3 05/12] l2tp: Add L2TPv3 protocol support James Chapman
2010-03-30 16:17 ` [PATCH v3 06/12] l2tp: Update PPP-over-L2TP driver to work over L2TPv3 James Chapman
2010-03-30 16:18 ` [PATCH v3 07/12] l2tp: Add L2TPv3 IP encapsulation (no UDP) support James Chapman
2010-03-30 16:18 ` [PATCH v3 08/12] netlink: Export genl_lock() API for use by modules James Chapman
2010-03-30 16:18 ` [PATCH v3 09/12] l2tp: Add netlink control API for L2TP James Chapman
2010-03-31 8:59 ` Patrick McHardy
2010-03-30 16:18 ` [PATCH v3 10/12] l2tp: Add L2TP ethernet pseudowire support James Chapman
2010-03-30 16:30 ` Stephen Hemminger
2010-03-30 16:30 ` Stephen Hemminger
2010-03-30 16:32 ` Stephen Hemminger
2010-03-31 9:35 ` James Chapman
2010-03-31 17:38 ` Paul E. McKenney
2010-04-02 15:24 ` Paul E. McKenney [this message]
2010-04-02 15:58 ` Eric Dumazet
2010-04-02 16:21 ` Paul E. McKenney
2010-03-30 16:18 ` [PATCH v3 11/12] l2tp: Add support for static unmanaged L2TPv3 tunnels James Chapman
2010-03-30 16:18 ` [PATCH v3 12/12] l2tp: Update documentation James Chapman
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=20100402152402.GA6017@linux.vnet.ibm.com \
--to=paulmck@linux$(echo .)vnet.ibm.com \
--cc=jchapman@katalix$(echo .)com \
--cc=netdev@vger$(echo .)kernel.org \
--cc=shemminger@vyatta$(echo .)com \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
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