Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1760498AbZFBLhr (ORCPT ); Tue, 2 Jun 2009 07:37:47 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1757990AbZFBLhh (ORCPT ); Tue, 2 Jun 2009 07:37:37 -0400 Received: from cantor2.suse.de ([195.135.220.15]:60454 "EHLO mx2.suse.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1755965AbZFBLhg (ORCPT ); Tue, 2 Jun 2009 07:37:36 -0400 Date: Tue, 2 Jun 2009 13:37:36 +0200 From: Jan Kara To: Wu Fengguang Cc: Eric Sandeen , Andrew Morton , LKML , Jan Kara , Masayoshi MIZUMA , "linux-fsdevel@vger.kernel.org" , "viro@zeniv.linux.org.uk" , Nick Piggin Subject: Re: [PATCH] skip I_CLEAR state inodes Message-ID: <20090602113736.GB15010@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> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20090602085523.GC7161@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: 3808 Lines: 97 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. > /* > @@ -518,7 +518,7 @@ void generic_sync_sb_inodes(struct super > if (current_is_pdflush() && !writeback_acquire(bdi)) > break; > > - BUG_ON(inode->i_state & I_FREEING); > + BUG_ON(inode->i_state & (I_FREEING | I_CLEAR)); > __iget(inode); > pages_skipped = wbc->pages_skipped; > __writeback_single_inode(inode, wbc); Looking at this code, it looks a bit suspicious. What prevents this s_io list scan to race with inode freeing? In particular generic_forget_inode() can drop inode_lock to write the inode and in the mean time generic_sync_sb_inodes() can come, get a reference to the inode and start it's writeback... Subsequent iput() would then call generic_forget_inode() on the inode again. So shouldn't we skip I_FREEING|I_CLEAR|I_WILL_FREE|I_NEW inodes in this scan like we do for later in the function for another scan? 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/