Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753237AbZFCOAd (ORCPT ); Wed, 3 Jun 2009 10:00:33 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1756046AbZFCOAI (ORCPT ); Wed, 3 Jun 2009 10:00:08 -0400 Received: from cantor2.suse.de ([195.135.220.15]:39314 "EHLO mx2.suse.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1755911AbZFCOAG (ORCPT ); Wed, 3 Jun 2009 10:00:06 -0400 Date: Wed, 3 Jun 2009 16:00:06 +0200 From: Jan Kara To: Wu Fengguang Cc: Jan Kara , Eric Sandeen , Andrew Morton , LKML , Masayoshi MIZUMA , "linux-fsdevel@vger.kernel.org" , "viro@zeniv.linux.org.uk" , Nick Piggin Subject: Re: [PATCH] skip I_CLEAR state inodes Message-ID: <20090603140005.GB5650@duck.suse.cz> References: <20090318170237.8F6C.61FB500B@jp.fujitsu.com> <20090323103846.GA16577@localhost> <20090324155655.2684.61FB500B@jp.fujitsu.com> <20090324074457.GA7745@localhost> <20090324120502.GC23439@duck.suse.cz> <20090324124001.GA25326@localhost> <4A244A5B.7070605@sandeen.net> <20090602085523.GC7161@localhost> <20090602113736.GB15010@duck.suse.cz> <20090603133202.GA5738@localhost> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20090603133202.GA5738@localhost> User-Agent: Mutt/1.5.17 (2007-11-01) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 4085 Lines: 94 On Wed 03-06-09 21:32:02, Wu Fengguang wrote: > [reply the easy part first] > On Tue, Jun 02, 2009 at 07:37:36PM +0800, Jan Kara wrote: > > On Tue 02-06-09 16:55:23, Wu Fengguang wrote: > > > On Tue, Jun 02, 2009 at 05:38:35AM +0800, Eric Sandeen wrote: > > > > Wu Fengguang wrote: > > > > > Add I_CLEAR tests to drop_pagecache_sb(), generic_sync_sb_inodes() and > > > > > add_dquot_ref(). > > > > > > > > > > clear_inode() will switch inode state from I_FREEING to I_CLEAR, > > > > > and do so _outside_ of inode_lock. So any I_FREEING testing is > > > > > incomplete without the testing of I_CLEAR. > > > > > > > > > > Masayoshi MIZUMA first discovered the bug in drop_pagecache_sb() and > > > > > Jan Kara reminds fixing the other two cases. Thanks! > > > > > > > > Is there a reason it's not done for __sync_single_inode as well? > > > > > > It missed the glance because it don't have an obvious '|' in the line ;) > > > > > > > Jeff Layton asked the question and I'm following it up :) > > > > > > > > __sync_single_inode currently only tests I_FREEING, but I think we are > > > > safe because __sync_single_inode sets I_SYNC, and clear_inode waits for > > > > I_SYNC to be cleared before it changes I_STATE. > > > > > > But I_SYNC is removed just before the I_FREEING test, so we still have > > > a small race window? > > > > > > > On the other hand, testing I_CLEAR here probably would be safe anyway, > > > > and it'd be bonus points for consistency? > > > > > > So let's add the I_CLEAR test? > > > > > > > Same basic question for generic_sync_sb_inodes, which has a > > > > BUG_ON(inode->i_state & I_FREEING), seems like this could check I_CLWAR > > > > as well? > > > > > > Yes, we can add I_CLEAR here to catch more error condition. > > > > > > Thanks, > > > Fengguang > > > > > > --- > > > skip I_CLEAR state inodes in writeback routines > > > > > > The I_FREEING test in __sync_single_inode() is racy because > > > clear_inode() can set i_state to I_CLEAR between the clear of I_SYNC > > > and the test of I_FREEING. > > > > > > Also extend the coverage of BUG_ON(I_FREEING) to I_CLEAR. > > > > > > Reported-by: Jeff Layton > > > Reported-by: Eric Sandeen > > > Signed-off-by: Wu Fengguang > > > --- > > > fs/fs-writeback.c | 4 ++-- > > > 1 file changed, 2 insertions(+), 2 deletions(-) > > > > > > --- linux.orig/fs/fs-writeback.c > > > +++ linux/fs/fs-writeback.c > > > @@ -316,7 +316,7 @@ __sync_single_inode(struct inode *inode, > > > spin_lock(&inode_lock); > > > WARN_ON(inode->i_state & I_NEW); > > > inode->i_state &= ~I_SYNC; > > > - if (!(inode->i_state & I_FREEING)) { > > > + if (!(inode->i_state & (I_FREEING | I_CLEAR))) { > > > if (!(inode->i_state & I_DIRTY) && > > > mapping_tagged(mapping, PAGECACHE_TAG_DIRTY)) { > > Is the whole if needed? I had an impression that everyone calling > > __sync_single_inode() should better take care it does not race with inode > > freeing... So WARN_ON would be more appropriate IMHO. > > The caller doesn't matter here, because we temporarily dropped inode_lock > in __sync_single_inode() ? But the problem is basically what I described in the part you cut from the email - if the caller of __sync_single_inode() does not have a reference to the inode or some other means of protecting inode from being released, then we have a problem because e.g. __writeback_single_inode() can sleep and before I_SYNC is set, all the clear_inode() can finish and we end up calling do_writepages() on invalidated mapping. So in my opinion everybody calling __writeback_single_inode() and thus __sync_single_inode() should do an equivalent of igrab() or be sure inode cannot be freed e.g. because we have a file open. Honza -- Jan Kara SUSE Labs, CR -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/