From mboxrd@z Thu Jan 1 00:00:00 1970 From: Peter Zijlstra Subject: Re: [PATCH 3/3] Convert the UDP hash lock to RCU Date: Tue, 07 Oct 2008 10:17:59 +0200 Message-ID: <1223367480.26330.7.camel@lappy.programming.kicks-ass.net> References: <20081006185026.GA10383@minyard.local> <48EA8197.6080502@cosmosbay.com> Mime-Version: 1.0 Content-Type: text/plain Content-Transfer-Encoding: 7bit Cc: minyard@acm.org, Linux Kernel , netdev@vger.kernel.org, shemminger@vyatta.com, paulmck@linux.vnet.ibm.com To: Eric Dumazet Return-path: In-Reply-To: <48EA8197.6080502@cosmosbay.com> Sender: linux-kernel-owner@vger.kernel.org List-Id: netdev.vger.kernel.org On Mon, 2008-10-06 at 23:22 +0200, Eric Dumazet wrote: > Or just add SLAB_DESTROY_BY_RCU to slab creation in proto_register() > for "struct proto udp_prot/udpv6_prot" so that kmem_cache_free() > done in sk_prot_free() can defer freeing to RCU... Be careful!, SLAB_DESTROY_BY_RCU just means the slab page gets RCU-freed, this means that slab object pointers stay pointing to valid memory, but it does _NOT_ mean those slab objects themselves remain valid. The slab allocator is free to re-use those objects at any time - irrespective of the rcu-grace period. Therefore you will have to be able to validate that the object you point to is indeed the object you expect, otherwise strange and wonderful things will happen.