From mboxrd@z Thu Jan 1 00:00:00 1970 Received: by zproxy.gmail.com with SMTP id l1so1193235nzf for ; Sun, 12 Mar 2006 19:04:53 -0800 (PST) Message-ID: <661de9470603121904h7e83579boe3b26013f771c0f2@mail.gmail.com> Date: Mon, 13 Mar 2006 08:34:53 +0530 From: "Balbir Singh" Subject: Re: [patch 1/3] radix tree: RCU lockless read-side In-Reply-To: <44128EDA.6010105@yahoo.com.au> MIME-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 8BIT Content-Disposition: inline References: <20060207021822.10002.30448.sendpatchset@linux.site> <20060207021831.10002.84268.sendpatchset@linux.site> <661de9470603110022i25baba63w4a79eb543c5db626@mail.gmail.com> <44128EDA.6010105@yahoo.com.au> Sender: owner-linux-mm@kvack.org Return-Path: To: Nick Piggin Cc: Nick Piggin , Linux Kernel , Linux Memory Management List-ID: On 3/11/06, Nick Piggin wrote: > Balbir Singh wrote: > > > > > >> if (slot->slots[i]) { > >>- results[nr_found++] = slot->slots[i]; > >>+ results[nr_found++] = &slot->slots[i]; > >> if (nr_found == max_items) > >> goto out; > >> } > > > > > > A quick clarification - Shouldn't accesses to slot->slots[i] above be > > protected using rcu_derefence()? > > > > I think we're safe here -- this is the _address_ of the pointer. > However, when dereferencing this address in _gang_lookup, > I think we do need rcu_dereference indeed. > Yes, I saw the address operator, but we still derefence "slots" to get the address. > Note that _gang_lookup_slot doesn't do this for us, however -- > the caller must do that when dereferencing the pointer to the > item (eg. see page_cache_get_speculative in 2/3). Oh! I did not get that far. Will look at the rest of the series > > That said, I'm not 100% sure I have the rcu memory barriers in > the right places (well I'm sure I don't, given the _gang_lookup > bug you exposed!). Hmm... Let me look at rcu_torture module and see if I can figure it out or read the documentation again. > > Thanks, > Nick > Warm Regards, Balbir -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: email@kvack.org