From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from bombadil.infradead.org ([65.50.211.133]:43643 "EHLO bombadil.infradead.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751484AbdISUli (ORCPT ); Tue, 19 Sep 2017 16:41:38 -0400 Date: Tue, 19 Sep 2017 13:41:35 -0700 From: Christoph Hellwig To: Waiman Long Cc: Christoph Hellwig , Jens Axboe , Steven Rostedt , Ingo Molnar , linux-kernel@vger.kernel.org, linux-fsdevel@vger.kernel.org, linux-block@vger.kernel.org, linux-nilfs@vger.kernel.org, cluster-devel@redhat.com, Bart Van Assche Subject: Re: [PATCH v6 1/2] blktrace: Fix potentail deadlock between delete & sysfs ops Message-ID: <20170919204135.GA7411@infradead.org> References: <1505760831-7747-1-git-send-email-longman@redhat.com> <1505760831-7747-2-git-send-email-longman@redhat.com> <20170919000155.GA30806@infradead.org> <20170919143811.GB15944@infradead.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: Sender: linux-fsdevel-owner@vger.kernel.org List-ID: On Tue, Sep 19, 2017 at 11:58:34AM -0400, Waiman Long wrote: > I was trying not to add a new mutex to a structure just for blktrace as > it is an optional feature that is enabled only if the > CONFIG_BLK_DEV_IO_TRACE config option is defined and it will only need > to be taken occasionally. So? Make the lock optional, too. > As filesystem freeze looks orthogonal to blktrace and the mutex also > looks to be used sparingly, I think it is a good match to overload it to > control blktrace as well. If the functionally is orthogonal that is a reason not to share a lock, not to the contrary. > I could modify the patch to use a mutex in the request_queue structure. > The current sysfs_lock mutex has about 74 references. So I am not > totally sure if it is safe to reuse. So the only option is to add > something like > > #ifdef CONFIG_BLK_DEV_IO_TRACE > struct mutex blktrace_mutex; > #endif > > to the request_queue structure. That structure is large enough that > adding a mutex won't increase the size much percentage-wise. Call it blk_trace mutex and move it right next to the blk_trace structure: ifdef CONFIG_BLK_DEV_IO_TRACE struct blk_trace *blk_trace; struct mutex blk_trace_mutex; #endif which makes it completely obvious to any read what you are protecting with it.