From f9114eba1eb08ee75fd0f1eee780f0290fb3c043 Mon Sep 17 00:00:00 2001 From: David Chinner Date: Wed, 17 Sep 2008 16:51:21 +1000 Subject: [PATCH] [XFS] Prevent lockdep false positives when locking two inodes. If we call xfs_lock_two_inodes() to grab both the iolock and the ilock, then drop the ilocks on both inodes, then grab them again (as xfs_swap_extents() does) then lockdep will report a locking order problem. This is a false positive. To avoid this, disallow xfs_lock_two_inodes() fom locking both inode locks at once - force calers to make two separate calls. This means that nested dropping and regaining of the ilocks will retain the same lockdep subclass and so lockdep will not see anything wrong with this code. SGI-PV: 986238 SGI-Modid: xfs-linux-melb:xfs-kern:31999a Signed-off-by: David Chinner Signed-off-by: Christoph Hellwig Signed-off-by: Peter Leckie Signed-off-by: Lachlan McIlroy --- fs/xfs/xfs_dfrag.c | 9 ++++++++- fs/xfs/xfs_vnodeops.c | 8 ++++++++ 2 files changed, 16 insertions(+), 1 deletion(-) diff --git a/fs/xfs/xfs_dfrag.c b/fs/xfs/xfs_dfrag.c index 760f4c5b5160..75b0cd4da0ea 100644 --- a/fs/xfs/xfs_dfrag.c +++ b/fs/xfs/xfs_dfrag.c @@ -149,7 +149,14 @@ xfs_swap_extents( sbp = &sxp->sx_stat; - xfs_lock_two_inodes(ip, tip, lock_flags); + /* + * we have to do two separate lock calls here to keep lockdep + * happy. If we try to get all the locks in one call, lock will + * report false positives when we drop the ILOCK and regain them + * below. + */ + xfs_lock_two_inodes(ip, tip, XFS_IOLOCK_EXCL); + xfs_lock_two_inodes(ip, tip, XFS_ILOCK_EXCL); locked = 1; /* Verify that both files have the same format */ diff --git a/fs/xfs/xfs_vnodeops.c b/fs/xfs/xfs_vnodeops.c index aa238c8fbd7a..98a0aecafddc 100644 --- a/fs/xfs/xfs_vnodeops.c +++ b/fs/xfs/xfs_vnodeops.c @@ -1838,6 +1838,12 @@ xfs_lock_inodes( #endif } +/* + * xfs_lock_two_inodes() can only be used to lock one type of lock + * at a time - the iolock or the ilock, but not both at once. If + * we lock both at once, lockdep will report false positives saying + * we have violated locking orders. + */ void xfs_lock_two_inodes( xfs_inode_t *ip0, @@ -1848,6 +1854,8 @@ xfs_lock_two_inodes( int attempts = 0; xfs_log_item_t *lp; + if (lock_mode & (XFS_IOLOCK_SHARED|XFS_IOLOCK_EXCL)) + ASSERT((lock_mode & (XFS_ILOCK_SHARED|XFS_ILOCK_EXCL)) == 0); ASSERT(ip0->i_ino != ip1->i_ino); if (ip0->i_ino > ip1->i_ino) { -- GitLab