From mboxrd@z Thu Jan 1 00:00:00 1970 Date: Mon, 13 Mar 2006 07:40:48 +0100 From: Nick Piggin Subject: Re: [patch 1/3] radix tree: RCU lockless read-side Message-ID: <20060313064047.GA2090@wotan.suse.de> References: <20060207021822.10002.30448.sendpatchset@linux.site> <20060207021831.10002.84268.sendpatchset@linux.site> <661de9470603110022i25baba63w4a79eb543c5db626@mail.gmail.com> <44128EDA.6010105@yahoo.com.au> <661de9470603121904h7e83579boe3b26013f771c0f2@mail.gmail.com> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <661de9470603121904h7e83579boe3b26013f771c0f2@mail.gmail.com> Sender: owner-linux-mm@kvack.org Return-Path: To: Balbir Singh Cc: Nick Piggin , Nick Piggin , Linux Kernel , Linux Memory Management List-ID: On Mon, Mar 13, 2006 at 08:34:53AM +0530, Balbir Singh wrote: > 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. > OK, I reread what you wrote and I misunderstood you earlier I guess. slot->slots[i] does dereference the pointer at the ith entry of slots, but &slot->slots[i] does not, it will return the same thing as slot->slots+i, which only dereferences 'slot' (which we've established to be safe). Even if &slot->slots[i] did, for some silly compiler, dereference the pointer, we never actually see it or use it so it should be harmless. Nick -- 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