From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from relay.sgi.com (relay2.corp.sgi.com [137.38.102.29]) by oss.sgi.com (Postfix) with ESMTP id 166D47F4E for ; Mon, 22 Jul 2013 17:56:44 -0500 (CDT) Received: from cuda.sgi.com (cuda2.sgi.com [192.48.176.25]) by relay2.corp.sgi.com (Postfix) with ESMTP id 0101F304051 for ; Mon, 22 Jul 2013 15:56:43 -0700 (PDT) Received: from ipmail07.adl2.internode.on.net (ipmail07.adl2.internode.on.net [150.101.137.131]) by cuda.sgi.com with ESMTP id YwIm5Sj6u2TCLJGi for ; Mon, 22 Jul 2013 15:56:42 -0700 (PDT) Date: Tue, 23 Jul 2013 08:56:40 +1000 From: Dave Chinner Subject: Re: [PATCH] xfs: di_flushiter considered harmful Message-ID: <20130722225640.GB19986@dastard> References: <1374488304-13044-1-git-send-email-david@fromorbit.com> <20130722110732.GA365@x4> MIME-Version: 1.0 Content-Disposition: inline In-Reply-To: <20130722110732.GA365@x4> List-Id: XFS Filesystem from SGI List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Errors-To: xfs-bounces@oss.sgi.com Sender: xfs-bounces@oss.sgi.com To: Markus Trippelsdorf Cc: xfs@oss.sgi.com On Mon, Jul 22, 2013 at 01:07:32PM +0200, Markus Trippelsdorf wrote: > On 2013.07.22 at 20:18 +1000, Dave Chinner wrote: > > From: Dave Chinner > > > > When we made all inode updates transactional, we no longer needed > > the log recovery detection for inodes being newer on disk than the > > transaction being replayed - it was redundant as replay of the log > > would always result in the latest version of the inode woul dbe on > > disk. It was redundant, but left in place because it wasn't > > considered to be a problem. > > > > However, with the new "don't read inodes on create" optimisation, > > flushiter has come back to bite us. Essentially, the optimisation > > made always initialises flushiter to zero in the create transaction, > > and so if we then crash and run recovery and the inode already on > > disk has a non-zero flushiter it will skip recovery of that inode. > > As a result, log recovery does the wrong thing and we end up with a > > corrupt filesystem. > > > > Because we have to support old kernel to new kernl upgrades, we > > can't just get rid of the flushiter support in log recovery as we > > might be upgrading from a kernel that doesn't have fully transaction > > inode updates. Unfortunately, for v4 superblocks there is no way to > > guarantee that log recovery knows about this fact. > > > > We cannot add a new inode format flag to say it's a "special inode > > create" because it won't be understood by older kernels and so > > recovery could do the wrong thing on downgrade. We cannot specially > > detect the combination of zero mode/non-zero flushiter on disk to > > non-zero mode, zero flushiter in the log item during recovery > > because wrapping of the flushiter can result in false detection. > > > > Hence that makes this "don't use flushiter" optimisation limited to > > a disk format that guarantees that we don't need it. And that means > > the only fix here is to limit the "no read IO on create" > > optimisation to version 5 superblocks.... > > I think your patch misses the following part: > > @@ -1054,17 +1056,15 @@ xfs_iread( > > /* shortcut IO on inode allocation if possible */ > if ((iget_flags & XFS_IGET_CREATE) && > - !(mp->m_flags & XFS_MOUNT_IKEEP)) { > + !(mp->m_flags & XFS_MOUNT_IKEEP) && > + xfs_sb_version_hascrc(&mp->m_sb)) { > /* initialise the on-disk inode core */ > memset(&ip->i_d, 0, sizeof(ip->i_d)); > ip->i_d.di_magic = XFS_DINODE_MAGIC; > ip->i_d.di_gen = prandom_u32(); > - if (xfs_sb_version_hascrc(&mp->m_sb)) { > - ip->i_d.di_version = 3; > - ip->i_d.di_ino = ip->i_ino; > - uuid_copy(&ip->i_d.di_uuid, &mp->m_sb.sb_uuid); > - } else > - ip->i_d.di_version = 2; > + ip->i_d.di_version = 3; > + ip->i_d.di_ino = ip->i_ino; > + uuid_copy(&ip->i_d.di_uuid, &mp->m_sb.sb_uuid); > return 0; > } Sure, it's dead code so doesn't affect the behaviour of the patch. I'll update it, but I need you to reproduce the problem in a simple manner as Mark did with this patch in place so I can find out what the real problem you are seeing is.... Cheers, Dave. -- Dave Chinner david@fromorbit.com _______________________________________________ xfs mailing list xfs@oss.sgi.com http://oss.sgi.com/mailman/listinfo/xfs