From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1757168Ab1JSRa7 (ORCPT ); Wed, 19 Oct 2011 13:30:59 -0400 Received: from mail-yw0-f46.google.com ([209.85.213.46]:47141 "EHLO mail-yw0-f46.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1755300Ab1JSRa6 (ORCPT ); Wed, 19 Oct 2011 13:30:58 -0400 Date: Wed, 19 Oct 2011 10:30:53 -0700 From: Tejun Heo To: Vivek Goyal Cc: axboe@kernel.dk, linux-kernel@vger.kernel.org, ctalbott@google.com Subject: Re: [PATCH 07/10] block: reorganize throtl_get_tg() and blk_throtl_bio() Message-ID: <20111019173053.GG25124@google.com> References: <1318998384-22525-1-git-send-email-tj@kernel.org> <1318998384-22525-8-git-send-email-tj@kernel.org> <20111019145622.GE1140@redhat.com> <20111019170625.GD25124@google.com> <20111019171917.GA4026@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20111019171917.GA4026@redhat.com> User-Agent: Mutt/1.5.20 (2009-06-14) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Hello, On Wed, Oct 19, 2011 at 01:19:17PM -0400, Vivek Goyal wrote: > > Currently, the code has different opportunistic checks which can catch > > most of those cases but unfortunatly I think it just makes the bugs > > more obscure. > > > > That said, we probably should be switching to internal lock once > > clenaup is complete. > > So even switching to internal lock is racy. Christoph suggeted to break down > this sharing of queue lock and driver lock and suggested always use > internal queue lock and modify drivers to use their own lock and manage it. > It makes sense though it might be lot of work to fix drivers. Hmmmm, yeah, right, switching itself would be racy. Maybe not sharing is the solution, I don't know. There's a way to make the switching safe tho. Sth like the following. lock_queue(q, flags) { spinlock_t *lock; local_irq_save(flags); lock = rcu_dereference_sched(q->queue_lock); spin_lock(lock); } and on cleanup, do synchronize_sched() after lock switching. But yeah it still stinks. Thanks. -- tejun