From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1756869Ab2GQVgp (ORCPT ); Tue, 17 Jul 2012 17:36:45 -0400 Received: from mail-pb0-f46.google.com ([209.85.160.46]:56754 "EHLO mail-pb0-f46.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1756828Ab2GQVgk (ORCPT ); Tue, 17 Jul 2012 17:36:40 -0400 Date: Tue, 17 Jul 2012 14:36:43 -0700 From: Olof Johansson To: tj@kernel.org Cc: axboe@kernel.dk, linux-kernel@vger.kernel.org, vgoyal@redhat.com, torvalds@linux-foundation.org Subject: [REGRESSION] [PATCH] block: uninitialized ioc->nr_tasks triggers WARN_ON Message-ID: <20120717213643.GA24726@quad.lixom.net> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline User-Agent: Mutt/1.5.21 (2010-09-15) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Hi, I'm using the old-fashioned 'dump' backup tool, and I noticed that it spews the below warning as of 3.5-rc1 and later (3.4 is fine): [ 10.886893] ------------[ cut here ]------------ [ 10.886904] WARNING: at include/linux/iocontext.h:140 copy_process+0x1488/0x1560() [ 10.886905] Hardware name: Bochs [ 10.886906] Modules linked in: [ 10.886908] Pid: 2430, comm: dump Not tainted 3.5.0-rc7+ #27 [ 10.886908] Call Trace: [ 10.886911] [] warn_slowpath_common+0x7a/0xb0 [ 10.886912] [] warn_slowpath_null+0x15/0x20 [ 10.886913] [] copy_process+0x1488/0x1560 [ 10.886914] [] do_fork+0xb4/0x340 [ 10.886918] [] ? recalc_sigpending+0x1a/0x50 [ 10.886919] [] ? __set_task_blocked+0x32/0x80 [ 10.886920] [] ? __set_current_blocked+0x3a/0x60 [ 10.886923] [] sys_clone+0x23/0x30 [ 10.886925] [] stub_clone+0x13/0x20 [ 10.886927] [] ? system_call_fastpath+0x16/0x1b [ 10.886928] ---[ end trace 32a14af7ee6a590b ]--- Reproducing is easy, I can hit it on a KVM system with a very basic config (x86_64 make defconfig + enable the drivers needed). To hit it, just install dump (on debian/ubuntu, not sure what the package might be called on Fedora), and: dump -o -f /tmp/foo / You'll see the warning in dmesg once it forks off the I/O process and starts dumping filesystem contents. I bisected it down to the following commit: commit f6e8d01bee036460e03bd4f6a79d014f98ba712e Author: Tejun Heo Date: Mon Mar 5 13:15:26 2012 -0800 block: add io_context->active_ref Currently ioc->nr_tasks is used to decide two things - whether an ioc is done issuing IOs and whether it's shared by multiple tasks. This patch separate out the first into ioc->active_ref, which is acquired and released using {get|put}_io_context_active() respectively. This will be used to associate bio's with a given task. This patch doesn't introduce any visible behavior change. Signed-off-by: Tejun Heo Cc: Vivek Goyal Signed-off-by: Jens Axboe It seems like the init of ioc->nr_tasks was removed in that patch, so it starts out at 0 instead of 1. Tejun, is the right thing here to add back the init, or should something else be done? The below patch removes the warning, but I haven't done any more extensive testing on it. Signed-off-by: Olof Johansson diff --git a/block/blk-ioc.c b/block/blk-ioc.c index 893b800..fab4cdd 100644 --- a/block/blk-ioc.c +++ b/block/blk-ioc.c @@ -244,6 +244,7 @@ int create_task_io_context(struct task_struct *task, gfp_t gfp_flags, int node) /* initialize */ atomic_long_set(&ioc->refcount, 1); + atomic_set(&ioc->nr_tasks, 1); atomic_set(&ioc->active_ref, 1); spin_lock_init(&ioc->lock); INIT_RADIX_TREE(&ioc->icq_tree, GFP_ATOMIC | __GFP_HIGH);