From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-2.5 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_PASS,USER_AGENT_MUTT autolearn=ham autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id CF8F6C28CF6 for ; Wed, 1 Aug 2018 23:20:01 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 50FF320862 for ; Wed, 1 Aug 2018 23:20:01 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 50FF320862 Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=ZenIV.linux.org.uk Authentication-Results: mail.kernel.org; spf=none smtp.mailfrom=linux-kernel-owner@vger.kernel.org Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1732272AbeHBBIJ (ORCPT ); Wed, 1 Aug 2018 21:08:09 -0400 Received: from zeniv.linux.org.uk ([195.92.253.2]:43136 "EHLO ZenIV.linux.org.uk" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726723AbeHBBIJ (ORCPT ); Wed, 1 Aug 2018 21:08:09 -0400 Received: from viro by ZenIV.linux.org.uk with local (Exim 4.87 #1 (Red Hat Linux)) id 1fl0PM-00039x-G9; Wed, 01 Aug 2018 23:19:56 +0000 Date: Thu, 2 Aug 2018 00:19:56 +0100 From: Al Viro To: Christoph Hellwig Cc: Avi Kivity , linux-aio@kvack.org, linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH 2/4] aio: add a iocb refcount Message-ID: <20180801231956.GS30522@ZenIV.linux.org.uk> References: <20180730071544.23998-1-hch@lst.de> <20180730071544.23998-3-hch@lst.de> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20180730071544.23998-3-hch@lst.de> User-Agent: Mutt/1.9.1 (2017-09-22) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Mon, Jul 30, 2018 at 09:15:42AM +0200, Christoph Hellwig wrote: > This is needed to prevent races caused by the way the ->poll API works. > To avoid introducing overhead for other users of the iocbs we initialize > it to zero and only do refcount operations if it is non-zero in the > completion path. refcount_t looks like a bad match - you, AFAICS, have count 0 for everything except poll, while for poll you start with 2. That looks like if (iocb->shared && test_and_clear_bit(0, &iocb->shared)) return; kill the sucker in your iocb_put() and initializing it to 1 in poll. No?