From mboxrd@z Thu Jan 1 00:00:00 1970 From: Jeff Layton Subject: Re: [PATCH] skip I_CLEAR state inodes Date: Tue, 2 Jun 2009 06:27:29 -0400 Message-ID: <20090602062729.03bdbe99@tupile.poochiereds.net> 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-Transfer-Encoding: 7bit Cc: Eric Sandeen , Andrew Morton , LKML , Jan Kara , Masayoshi MIZUMA , "linux-fsdevel@vger.kernel.org" , "viro@zeniv.linux.org.uk" , Nick Piggin To: Wu Fengguang Return-path: Received: from mx2.redhat.com ([66.187.237.31]:55636 "EHLO mx2.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752941AbZFBK1y (ORCPT ); Tue, 2 Jun 2009 06:27:54 -0400 In-Reply-To: <20090602085523.GC7161@localhost> Sender: linux-fsdevel-owner@vger.kernel.org List-ID: On Tue, 2 Jun 2009 16:55:23 +0800 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? > Yes, I think so. __sync_single_inode clears I_SYNC but doesn't wake up the wait queue until the end of the function. So I think it's possible (though unlikely) that another thread can race in and change the state to I_CLEAR before the I_FREEING check. > > 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)) { > /* > @@ -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); Acked-by: Jeff Layton