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Date: Tue, 07 Oct 2008 09:45:43 -0500 From: Christoph Lameter <cl@...ux-foundation.org> To: paulmck@...ux.vnet.ibm.com CC: Evgeniy Polyakov <johnpol@....mipt.ru>, Corey Minyard <minyard@....org>, David Miller <davem@...emloft.net>, dada1@...mosbay.com, linux-kernel@...r.kernel.org, netdev@...r.kernel.org, shemminger@...tta.com Subject: Re: [PATCH 3/3] Convert the UDP hash lock to RCU 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. -- To unsubscribe from this list: send the line "unsubscribe netdev" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
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