From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: with ECARTIS (v1.0.0; list xfs); Tue, 05 Jun 2007 22:38:01 -0700 (PDT) Received: from larry.melbourne.sgi.com (larry.melbourne.sgi.com [134.14.52.130]) by oss.sgi.com (8.12.10/8.12.10/SuSE Linux 0.7) with SMTP id l565btWt017471 for ; Tue, 5 Jun 2007 22:37:57 -0700 Date: Wed, 6 Jun 2007 15:37:48 +1000 From: David Chinner Subject: review: prevent log tail-pushing unmount deadlock Message-ID: <20070606053748.GV86004887@sgi.com> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline Sender: xfs-bounce@oss.sgi.com Errors-to: xfs-bounce@oss.sgi.com List-Id: xfs To: xfs-dev Cc: xfs-oss When we are unmounting the filesystem, we flush all the inodes to disk. Unfortunately, if we have an inode cluster that has just been freed and marked stale sitting in an incore log buffer (i.e. hasn't been flushed to disk), it will be holding all the flush locks on the inodes in that cluster. xfs_iflush_all() which is called during unmount walks all the inodes trying to reclaim them, and it doing so calls xfs_finish_reclaim() on each inode. If the inode is dirty, if grabs the flush lock and flushes it. Unfortunately, find dirty inodes that already have their flush lock held and so we sleep. At this point in the unmount process, we are running single-threaded. There is nothing more that can push on the log to force the transaction holding the inode flush locks to disk and hence we deadlock. The fix is to issue a log force before flushing the inodes on unmount so that all the flush locks will be released before we start flushing the inodes. Recently discovered during testing with filestreams enabled. Cheers, Dave. -- Dave Chinner Principal Engineer SGI Australian Software Group --- fs/xfs/xfs_mount.c | 11 +++++++++++ 1 file changed, 11 insertions(+) Index: 2.6.x-xfs-new/fs/xfs/xfs_mount.c =================================================================== --- 2.6.x-xfs-new.orig/fs/xfs/xfs_mount.c 2007-04-19 13:47:41.272642686 +1000 +++ 2.6.x-xfs-new/fs/xfs/xfs_mount.c 2007-04-19 13:49:53.643581957 +1000 @@ -1162,6 +1162,17 @@ xfs_unmountfs(xfs_mount_t *mp, struct cr int64_t fsid; #endif + /* + * We can potentially deadlock here if we have an inode cluster + * that has been freed has it's buffer still pinned in memory because + * the transaction is still sitting in a iclog. The stale inodes + * on that buffer will have their flush locks held until the + * transaction hits the disk and the callbacks run. the inode + * flush takes the flush lock unconditionally and with nothing to + * push out the iclog we will never get that unlocked. hence we + * need to force the log first. + */ + xfs_log_force(mp, (xfs_lsn_t)0, XFS_LOG_FORCE | XFS_LOG_SYNC); xfs_iflush_all(mp); XFS_QM_DQPURGEALL(mp, XFS_QMOPT_QUOTALL | XFS_QMOPT_UMOUNTING);