From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mx2.suse.de ([195.135.220.15]:36861 "EHLO mx2.suse.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751085AbbLBKfQ (ORCPT ); Wed, 2 Dec 2015 05:35:16 -0500 Date: Wed, 2 Dec 2015 11:35:12 +0100 From: Jan Kara To: Dan Williams Cc: linux-fsdevel@vger.kernel.org, linux-block@vger.kernel.org, linux-nvdimm@lists.01.org, Dave Chinner , Jens Axboe , Jan Kara , Tejun Heo Subject: Re: [PATCH 3/3] writeback: fix false positive WARN in __mark_inode_dirty Message-ID: <20151202103512.GA22125@quack.suse.cz> References: <20151201235836.36836.90416.stgit@dwillia2-desk3.jf.intel.com> <20151201235852.36836.87208.stgit@dwillia2-desk3.jf.intel.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20151201235852.36836.87208.stgit@dwillia2-desk3.jf.intel.com> Sender: linux-fsdevel-owner@vger.kernel.org List-ID: On Tue 01-12-15 15:58:52, Dan Williams wrote: > This warning was added as a debugging aid way back in commit > 500b067c5e6c "writeback: check for registered bdi in flusher add and > inode dirty" when we were switching over to per-bdi writeback. > > Once the block device has been torn down it's no longer useful to > complain about unregistered bdi's. Clear the writeback capability under > the the wb->list_lock(), so that __mark_inode_dirty has no opportunity > to race bdi_unregister() to this WARN() condition. > > Alternatively we could just delete the warning... > > Found this while testing block device remove from underneath an active > fs triggering traces like: > > WARNING: CPU: 6 PID: 2129 at fs/fs-writeback.c:2065 __mark_inode_dirty+0x261/0x350() > bdi-block not registered > [..] > Call Trace: > [] dump_stack+0x44/0x62 > [] warn_slowpath_common+0x82/0xc0 > [] warn_slowpath_fmt+0x5c/0x80 > [] __mark_inode_dirty+0x261/0x350 > [] generic_update_time+0x79/0xd0 > [] file_update_time+0xbd/0x110 > [] ext4_dax_fault+0x68/0x110 > [] __do_fault+0x4e/0xf0 > [] handle_mm_fault+0x5e7/0x1b50 > [] ? handle_mm_fault+0x51/0x1b50 > [] __do_page_fault+0x191/0x3f0 > [] trace_do_page_fault+0x4f/0x120 > [] do_async_page_fault+0x1a/0xa0 > [] async_page_fault+0x28/0x30 > > Cc: Jan Kara > Cc: Tejun Heo > Cc: Jens Axboe > Cc: Dave Chinner > Signed-off-by: Dan Williams OK, looks good to me. There is still a tiny race window where the warning could trigger but I don't think it's worth caring about. You can add: Reviewed-by: Jan Kara Honza > --- > mm/backing-dev.c | 7 +++++++ > 1 file changed, 7 insertions(+) > > diff --git a/mm/backing-dev.c b/mm/backing-dev.c > index 8ed2ffd963c5..24e61acf74a7 100644 > --- a/mm/backing-dev.c > +++ b/mm/backing-dev.c > @@ -343,10 +343,17 @@ static void wb_shutdown(struct bdi_writeback *wb) > { > /* Make sure nobody queues further work */ > spin_lock_bh(&wb->work_lock); > + > if (!test_and_clear_bit(WB_registered, &wb->state)) { > spin_unlock_bh(&wb->work_lock); > return; > } > + > + /* tell __mark_inode_dirty that writeback is no longer possible */ > + spin_lock(&wb->list_lock); > + wb->bdi->capabilities |= BDI_CAP_NO_WRITEBACK; > + spin_unlock(&wb->list_lock); > + > spin_unlock_bh(&wb->work_lock); > > /* > > -- Jan Kara SUSE Labs, CR