Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S933086AbcDYRvV (ORCPT ); Mon, 25 Apr 2016 13:51:21 -0400 Received: from mail-yw0-f175.google.com ([209.85.161.175]:35575 "EHLO mail-yw0-f175.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S932191AbcDYRvU (ORCPT ); Mon, 25 Apr 2016 13:51:20 -0400 Date: Mon, 25 Apr 2016 13:51:15 -0400 From: Tejun Heo To: Roman Penyaev Cc: Jens Axboe , linux-block@vger.kernel.org, linux-kernel@vger.kernel.org, David Howells Subject: Re: [PATCH 1/1] [RFC] workqueue: fix ghost PENDING flag while doing MQ IO Message-ID: <20160425175115.GC7822@mtj.duckdns.org> References: <1461597771-25352-1-git-send-email-roman.penyaev@profitbricks.com> <20160425154847.GZ7822@mtj.duckdns.org> <20160425170304.GB7822@mtj.duckdns.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.5.24 (2015-08-30) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 785 Lines: 27 Hello, Roman. On Mon, Apr 25, 2016 at 07:39:52PM +0200, Roman Penyaev wrote: > Ok, that's clear now. Thanks. I was confused also by a spin lock, which > is being released just after clear pending: > > set_work_pool_and_clear_pending(work, pool->id); > spin_unlock_irq(&pool->lock); > ... > worker->current_func(work); > > But seems memory operations of execution can leak-in and appear before > pended bit is cleared and spin lock is released. > (according to Documentation/memory-barriers.txt, (6) RELEASE operations) Yeap, release doesn't prevent following reads from creeping ahead of it. > Tejun, do you need an updated patch for that? With a proper smp_mb()? Yes, can you please also add comment explaining what the mb is interlocking? Thanks a lot! -- tejun