From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755428Ab0KIWsS (ORCPT ); Tue, 9 Nov 2010 17:48:18 -0500 Received: from smtp1.linux-foundation.org ([140.211.169.13]:57771 "EHLO smtp1.linux-foundation.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754424Ab0KIWsP (ORCPT ); Tue, 9 Nov 2010 17:48:15 -0500 Date: Tue, 9 Nov 2010 14:47:28 -0800 From: Andrew Morton To: Wu Fengguang Cc: Jan Kara , linux-fsdevel@vger.kernel.org, linux-mm@kvack.org, Johannes Weiner , Christoph Hellwig , Jan Engelhardt , LKML Subject: Re: [PATCH 5/5] writeback: check skipped pages on WB_SYNC_ALL Message-Id: <20101109144728.d405453d.akpm@linux-foundation.org> In-Reply-To: <20101108231727.275529265@intel.com> References: <20101108230916.826791396@intel.com> <20101108231727.275529265@intel.com> X-Mailer: Sylpheed 2.4.8 (GTK+ 2.12.9; x86_64-pc-linux-gnu) Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue, 09 Nov 2010 07:09:21 +0800 Wu Fengguang wrote: > In WB_SYNC_ALL mode, filesystems are not expected to skip dirty pages on > temporal lock contentions or non fatal errors, otherwise sync() will > return without actually syncing the skipped pages. Add a check to > catch possible redirty_page_for_writepage() callers that violate this > expectation. > > I'd recommend to keep this check in -mm tree for some time and fixup the > possible warnings before pushing it to upstream. > > Signed-off-by: Wu Fengguang > --- > fs/fs-writeback.c | 1 + > 1 file changed, 1 insertion(+) > > --- linux-next.orig/fs/fs-writeback.c 2010-11-07 22:01:06.000000000 +0800 > +++ linux-next/fs/fs-writeback.c 2010-11-07 22:01:15.000000000 +0800 > @@ -527,6 +527,7 @@ static int writeback_sb_inodes(struct su > * buffers. Skip this inode for now. > */ > redirty_tail(inode); > + WARN_ON_ONCE(wbc->sync_mode == WB_SYNC_ALL); > } > spin_unlock(&inode_lock); > iput(inode); This is quite kernel-developer-unfriendly. Suppose the warning triggers. Now some poor schmuck looks at the warning and doesn't have a *clue* why it was added. He has to run off and grovel through git trees finding changelogs, which is a real pain if the code has been trivially altered since it was first added. As a general rule, a kernel developer should be able to look at a warning callsite and then work out why the warning was emitted! IOW, you owe us a code comment, please.