From: Christoph Lameter <cl@linux-foundation.org>
To: paulmck@linux.vnet.ibm.com
Cc: Evgeniy Polyakov <johnpol@2ka.mipt.ru>,
Corey Minyard <minyard@acm.org>,
David Miller <davem@davemloft.net>,
dada1@cosmosbay.com, linux-kernel@vger.kernel.org,
netdev@vger.kernel.org, shemminger@vyatta.com
Subject: Re: [PATCH 3/3] Convert the UDP hash lock to RCU
Date: Tue, 07 Oct 2008 09:45:43 -0500 [thread overview]
Message-ID: <48EB7617.3060304@linux-foundation.org> (raw)
In-Reply-To: <20081007143346.GA6384@linux.vnet.ibm.com>
Paul E. McKenney wrote:
> But care is required -- SLAB_DESTROY_BY_RCU permits objects to be freed
> and reallocated while a reader holds a reference. The only guarantee is
> that the -type- of the data structure will not change while a reader holds
> a reference. With something like UDP, this might well be sufficient.
Right so after the hash lookup operation you are not assured that the object
has not been freed or even reallocated for a different purpose. So after
finding the pointer to the object two things need to happen (under rcu_lock):
1. Verify that the object is still in use
2. Verify that the object is matching the hash
If not then the operation needs to be redone because we have a stale hash pointer.
next prev parent reply other threads:[~2008-10-07 14:54 UTC|newest]
Thread overview: 36+ messages / expand[flat|nested] mbox.gz Atom feed top
2008-10-06 18:50 [PATCH 3/3] Convert the UDP hash lock to RCU Corey Minyard
2008-10-06 21:22 ` Eric Dumazet
2008-10-06 21:40 ` David Miller
2008-10-06 23:08 ` Corey Minyard
2008-10-07 8:37 ` Evgeniy Polyakov
2008-10-07 14:16 ` Christoph Lameter
2008-10-07 14:29 ` Evgeniy Polyakov
2008-10-07 14:38 ` Christoph Lameter
2008-10-07 14:33 ` Paul E. McKenney
2008-10-07 14:45 ` Christoph Lameter [this message]
2008-10-07 15:07 ` Eric Dumazet
2008-10-07 15:07 ` Paul E. McKenney
2008-10-07 5:24 ` Eric Dumazet
2008-10-07 8:54 ` Benny Amorsen
2008-10-07 12:59 ` Eric Dumazet
2008-10-07 14:07 ` Stephen Hemminger
2008-10-07 20:55 ` David Miller
2008-10-07 21:20 ` Stephen Hemminger
2008-10-08 13:55 ` Eric Dumazet
2008-10-08 18:45 ` David Miller
2008-10-07 16:43 ` Corey Minyard
2008-10-07 18:26 ` David Miller
2008-10-08 8:35 ` Eric Dumazet
2008-10-08 16:38 ` David Miller
2008-10-07 8:31 ` Peter Zijlstra
2008-10-07 14:36 ` Paul E. McKenney
2008-10-07 18:29 ` David Miller
2008-10-06 22:07 ` Corey Minyard
2008-10-07 8:17 ` Peter Zijlstra
2008-10-07 9:24 ` Eric Dumazet
2008-10-07 14:15 ` Christoph Lameter
2008-10-07 14:38 ` Paul E. McKenney
2008-10-07 14:50 ` Eric Dumazet
2008-10-07 15:05 ` Paul E. McKenney
2008-10-07 15:09 ` Peter Zijlstra
2008-10-07 15:23 ` Christoph Lameter
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