From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753542Ab1J0Aez (ORCPT ); Wed, 26 Oct 2011 20:34:55 -0400 Received: from mga09.intel.com ([134.134.136.24]:20440 "EHLO mga09.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751313Ab1J0Aez (ORCPT ); Wed, 26 Oct 2011 20:34:55 -0400 X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="4.67,351,1309762800"; d="scan'208";a="67922223" Subject: Re: Multi-partition block layer behaviour From: Shaohua Li To: Tiju Jacob Cc: "linux-kernel@vger.kernel.org" In-Reply-To: References: Content-Type: text/plain; charset="UTF-8" Date: Thu, 27 Oct 2011 08:42:41 +0800 Message-ID: <1319676161.22361.148.camel@sli10-conroe> Mime-Version: 1.0 X-Mailer: Evolution 2.32.2 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed, 2011-10-26 at 18:10 +0800, Tiju Jacob wrote: > >> 1. When an I/O request is made to the filesystem, process 'A' acquires > >> a mutex FS lock and a mutex block driver lock. > >> > >> 2. Process 'B' tries to acquire the mutex FS lock, which is not > >> available. Hence, it goes to sleep. Due to the new plugging mechanism, > >> before going to sleep, shcedule() is invoked which disables preemption > >> and the context becomes atomic. In schedule(), the newly added > >> blk_flush_plug_list() is invoked which unplugs the block driver. > >> > >> 3) During unplug operation the block driver tries to acquire the mutex > >> lock which fails, because the lock was held by process 'A'. Previous > >> invocation of scheudle() in step 2 has already made the context as > >> atomic, hence the error "Schedule while atomic" occured. > > if blk_flush_plug_list() is called in schedule(), it will use > > blk_run_queue_async > > to unplug the queue. This runs in a workqueue. So how could this happen? > > > > The call stack goes as follows: > > From schedule() it calls blk_schedule_flush_plug() and > blk_flush_plug_list() gets invoked. > > In blk_flush_plug_list() queue_unplugged() does not get invoked. Hence > blk_run_queue_async is not called. > Instead __elv_add_request() is invoked with ELEVATOR_INSERT_SORT_MERGE > flag and the flag gets reassigned to ELEVATOR_INSERT_BACK. > > In ELEVATOR_INSERT_BACK, __blk_run_queue() gets invoked and calls request_fn(). This doesn't make sense. why the flag is changed from ELEVATOR_INSERT_SORT_MERGE to ELEVATOR_INSERT_BACK? can you post a full log? or did your driver have something special?