From: Herbert Xu <herbert@gondor.apana.org.au>
To: "Paul E. McKenney" <paulmck@linux.vnet.ibm.com>
Cc: "David S. Miller" <davem@davemloft.net>,
netdev@vger.kernel.org, Stephen Hemminger <shemminger@vyatta.com>
Subject: Re: [PATCH 6/13] bridge: Add core IGMP snooping support
Date: Sat, 6 Mar 2010 09:17:18 +0800 [thread overview]
Message-ID: <20100306011718.GA12812@gondor.apana.org.au> (raw)
In-Reply-To: <20100305234327.GJ6764@linux.vnet.ibm.com>
On Fri, Mar 05, 2010 at 03:43:27PM -0800, Paul E. McKenney wrote:
>
> Cool!!! You use a pair of list_head structures, so that a given
> element can be in both the old and the new hash table simultaneously.
> Of course, an RCU grace period must elapse between consecutive resizings.
> Which appears to be addressed.
Thanks :) I will try to extend this to other existing hash tables
where the number of updates can be limited like it is here.
> The teardown needs an rcu_barrier_bh() rather than the current
> synchronize_rcu_bh(), please see below.
All the call_rcu_bh's are done under multicast_lock. The first
check taken after taking the multicast_lock is whether we've
started the tear-down. So where it currently calls synchronize()
it should already be the case that no call_rcu_bh's are still
running.
> Also, I don't see how the teardown code is preventing new readers from
> finding the data structures before they are being passed to call_rcu_bh().
> You can't safely start the RCU grace period until -after- all new readers
> have been excluded. (But I could easily be missing something here.)
I understand. However, AFAICS whatever it is that we are destroying
is taken off the reader's visible data structure before call_rcu_bh.
Do you have a particular case in mind where this is not the case?
> The br_multicast_del_pg() looks to need rcu_read_lock_bh() and
> rcu_read_unlock_bh() around its loop, if I understand the pointer-walking
> scheme correctly.
Any function that modifies the data structure is done under the
multicast_lock, including br_multicast_del_pg.
> Hmmm... Where is the read-side code? Wherever it is, it cannot safely
> dereference the ->old pointer.
Right, the old pointer is merely there to limit rehashings to one
per window. So it isn't used by the read-side.
The read-side is the data path (non-IGMP multicast packets). The
sole entry point is br_mdb_get().
Cheers,
--
Visit Openswan at http://www.openswan.org/
Email: Herbert Xu ~{PmV>HI~} <herbert@gondor.apana.org.au>
Home Page: http://gondor.apana.org.au/~herbert/
PGP Key: http://gondor.apana.org.au/~herbert/pubkey.txt
next prev parent reply other threads:[~2010-03-06 1:17 UTC|newest]
Thread overview: 81+ messages / expand[flat|nested] mbox.gz Atom feed top
2010-02-26 15:34 [RFC] [1/13] bridge: Add IGMP snooping support Herbert Xu
2010-02-26 15:35 ` [PATCH 1/13] bridge: Do br_pass_frame_up after other ports Herbert Xu
2010-02-26 15:35 ` [PATCH 2/13] bridge: Allow tail-call on br_pass_frame_up Herbert Xu
2010-02-27 11:14 ` David Miller
2010-02-27 15:36 ` Herbert Xu
2010-02-26 15:35 ` [PATCH 3/13] bridge: Avoid unnecessary clone on forward path Herbert Xu
2010-02-26 15:35 ` [PATCH 4/13] bridge: Use BR_INPUT_SKB_CB on xmit path Herbert Xu
2010-02-26 15:35 ` [PATCH 5/13] bridge: Split may_deliver/deliver_clone out of br_flood Herbert Xu
2010-02-26 15:35 ` [PATCH 6/13] bridge: Add core IGMP snooping support Herbert Xu
2010-02-26 15:35 ` [PATCH 7/13] bridge: Add multicast forwarding functions Herbert Xu
2010-02-26 15:35 ` [PATCH 8/13] bridge: Add multicast start/stop hooks Herbert Xu
2010-02-26 15:35 ` [PATCH 9/13] bridge: Add multicast data-path hooks Herbert Xu
2010-02-26 15:35 ` [PATCH 10/13] bridge: Add multicast_router sysfs entries Herbert Xu
2010-02-27 0:42 ` Stephen Hemminger
2010-02-27 11:29 ` David Miller
2010-02-27 15:53 ` Herbert Xu
2010-03-09 12:25 ` Herbert Xu
2010-03-09 12:26 ` Herbert Xu
2010-02-26 15:35 ` [PATCH 11/13] bridge: Add multicast_snooping sysfs toggle Herbert Xu
2010-02-26 15:35 ` [PATCH 12/13] bridge: Add hash elasticity/max sysfs entries Herbert Xu
2010-02-26 15:35 ` [PATCH 13/13] bridge: Add multicast count/interval " Herbert Xu
2010-02-28 5:40 ` [1/13] bridge: Add IGMP snooping support Herbert Xu
2010-02-28 5:41 ` [PATCH 1/13] bridge: Do br_pass_frame_up after other ports Herbert Xu
2010-02-28 5:41 ` [PATCH 2/13] bridge: Allow tail-call on br_pass_frame_up Herbert Xu
2010-02-28 5:41 ` [PATCH 3/13] bridge: Avoid unnecessary clone on forward path Herbert Xu
2010-02-28 5:41 ` [PATCH 4/13] bridge: Use BR_INPUT_SKB_CB on xmit path Herbert Xu
2010-02-28 5:41 ` [PATCH 5/13] bridge: Split may_deliver/deliver_clone out of br_flood Herbert Xu
2010-02-28 5:41 ` [PATCH 6/13] bridge: Add core IGMP snooping support Herbert Xu
2010-03-05 23:43 ` Paul E. McKenney
2010-03-06 1:17 ` Herbert Xu [this message]
2010-03-06 5:06 ` Paul E. McKenney
2010-03-06 6:56 ` Herbert Xu
2010-03-06 7:03 ` Herbert Xu
2010-03-07 23:31 ` David Miller
2010-03-06 7:07 ` Herbert Xu
2010-03-07 23:31 ` David Miller
2010-03-06 15:00 ` Paul E. McKenney
2010-03-06 15:19 ` Paul E. McKenney
2010-03-06 19:00 ` Paul E. McKenney
2010-03-07 2:45 ` Herbert Xu
2010-03-07 3:11 ` Paul E. McKenney
2010-03-08 18:50 ` Arnd Bergmann
2010-03-09 3:15 ` Paul E. McKenney
2010-03-11 18:49 ` Arnd Bergmann
2010-03-14 23:01 ` Paul E. McKenney
2010-03-09 21:12 ` Arnd Bergmann
2010-03-10 2:14 ` Paul E. McKenney
2010-03-10 9:41 ` Arnd Bergmann
2010-03-10 10:39 ` Eric Dumazet
2010-03-10 10:49 ` Herbert Xu
2010-03-10 13:13 ` Paul E. McKenney
2010-03-10 14:07 ` Herbert Xu
2010-03-10 16:26 ` Paul E. McKenney
2010-03-10 16:35 ` David Miller
2010-03-10 17:56 ` Arnd Bergmann
2010-03-10 21:25 ` Paul E. McKenney
2010-03-10 13:27 ` Arnd Bergmann
2010-03-10 13:39 ` Arnd Bergmann
2010-03-10 13:19 ` Paul E. McKenney
2010-03-10 13:30 ` Arnd Bergmann
2010-03-10 13:57 ` Paul E. McKenney
2010-02-28 5:41 ` [PATCH 7/13] bridge: Add multicast forwarding functions Herbert Xu
2010-02-28 5:41 ` [PATCH 8/13] bridge: Add multicast start/stop hooks Herbert Xu
2010-02-28 5:41 ` [PATCH 9/13] bridge: Add multicast data-path hooks Herbert Xu
2010-04-27 17:13 ` [PATCH net-next] bridge: use is_multicast_ether_addr Stephen Hemminger
2010-04-27 19:53 ` David Miller
2010-02-28 5:41 ` [PATCH 10/13] bridge: Add multicast_router sysfs entries Herbert Xu
2010-04-27 17:13 ` [PATCH net-next] bridge: multicast router list manipulation Stephen Hemminger
2010-04-27 19:54 ` David Miller
2010-04-27 23:11 ` Michał Mirosław
2010-04-27 23:25 ` Stephen Hemminger
2010-04-27 23:28 ` David Miller
2010-04-27 23:44 ` Stephen Hemminger
2010-04-27 23:51 ` David Miller
2010-04-27 23:27 ` David Miller
2010-04-28 1:51 ` Herbert Xu
2010-02-28 5:41 ` [PATCH 11/13] bridge: Add multicast_snooping sysfs toggle Herbert Xu
2010-02-28 5:41 ` [PATCH 12/13] bridge: Add hash elasticity/max sysfs entries Herbert Xu
2010-02-28 5:41 ` [PATCH 13/13] bridge: Add multicast count/interval " Herbert Xu
2010-02-28 8:52 ` [1/13] bridge: Add IGMP snooping support David Miller
2010-03-01 2:08 ` Herbert Xu
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