From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755009Ab2JISiE (ORCPT ); Tue, 9 Oct 2012 14:38:04 -0400 Received: from mx1.redhat.com ([209.132.183.28]:30363 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752871Ab2JISiB (ORCPT ); Tue, 9 Oct 2012 14:38:01 -0400 Date: Tue, 9 Oct 2012 11:37:53 -0700 From: Zach Brown To: Kent Overstreet Cc: linux-bcache@vger.kernel.org, linux-kernel@vger.kernel.org, dm-devel@redhat.com, tytso@mit.edu Subject: Re: [PATCH 5/5] aio: Refactor aio_read_evt, use cmxchg(), fix bug Message-ID: <20121009183753.GP26187@lenny.home.zabbo.net> References: <1349764760-21093-1-git-send-email-koverstreet@google.com> <1349764760-21093-5-git-send-email-koverstreet@google.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <1349764760-21093-5-git-send-email-koverstreet@google.com> User-Agent: Mutt/1.5.21 (2010-09-15) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Mon, Oct 08, 2012 at 11:39:20PM -0700, Kent Overstreet wrote: > Bunch of cleanup Ugh. That's way too much noisy change for one patch with no description. Break it up into functional pieces and actually describe them. > events off the ringbuffer without racing with io_getevents(). Are you sure this is safe in the presence of wrapping indices? It's been a very long time since I've looked at this, but I could never convince myself that it was safe. What I'm worried about is cmpxchg()s caller sampling, say, and index of 0, having another task GO NUTS and wrap that index all the way around back to 0, and then having that initial cmpchg() caller see the wrapped 0 index and think that's nothing's changed in the interim. Is this a problem? (I wish I could find the comment I wrote in a very old patch to tear out the mapped ring entirely.. It was a great list of its design mistakes.) - z