From mboxrd@z Thu Jan 1 00:00:00 1970 From: William Allen Simpson Subject: Re: [net-next-2.6 PATCH RFC] TCPCT part 1d: generate Responder Cookie Date: Thu, 05 Nov 2009 07:45:24 -0500 Message-ID: <4AF2C8E4.9020202@gmail.com> References: <4AEAC763.4070200@gmail.com> <4AED86AD.6010906@gmail.com> <4AEDCD7C.2010403@gmail.com> <4AF0B0D2.4030905@gmail.com> <20091104214844.GA6714@linux.vnet.ibm.com> <4AF2C266.1010603@gmail.com> Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit Cc: Eric Dumazet , Linux Kernel Developers , Linux Kernel Network Developers To: paulmck@linux.vnet.ibm.com Return-path: In-Reply-To: <4AF2C266.1010603@gmail.com> Sender: linux-kernel-owner@vger.kernel.org List-Id: netdev.vger.kernel.org William Allen Simpson wrote: > Yes. Just shuffling the pointers without ever freeing anything. So, > there's nothing for call_rcu() to do, and nothing else to synchronize > (only the pointers). This assumes that after _unlock_ any CPU cache > with an old pointer->expires will hit the _lock_ code, and that will > update *both* ->expires and the other array elements concurrently? > Reiterating, I've not found Documentation showing that this code works: + unsigned long jiffy = jiffies; + + if (unlikely(time_after(jiffy, tcp_secret_generating->expires))) { + spin_lock_bh(&tcp_secret_locker); + if (!time_after(jiffy, tcp_secret_generating->expires)) { + /* refreshed by another */ + spin_unlock_bh(&tcp_secret_locker); + memcpy(&xvp->cookie_bakery[0], + &tcp_secret_generating->secrets[0], + sizeof(tcp_secret_generating->secrets)); + } else { How is it ensured that an old tcp_secret_generating or an old ->expires, followed by a spin_lock, has updated both? And even when both are updated, then every word of the ->secrets array has also been updated in the local cache? Is this a property of spin_lock()? Or spin_unlock()?