From 653c60b633a9019a54a80d64b5ed33ecb214823c Mon Sep 17 00:00:00 2001 From: Dave Chinner Date: Mon, 23 Feb 2015 21:43:37 +1100 Subject: xfs: introduce mmap/truncate lock Right now we cannot serialise mmap against truncate or hole punch sanely. ->page_mkwrite is not able to take locks that the read IO path normally takes (i.e. the inode iolock) because that could result in lock inversions (read - iolock - page fault - page_mkwrite - iolock) and so we cannot use an IO path lock to serialise page write faults against truncate operations. Instead, introduce a new lock that is used *only* in the ->page_mkwrite path that is the equivalent of the iolock. The lock ordering in a page fault is i_mmaplock -> page lock -> i_ilock, and so in truncate we can i_iolock -> i_mmaplock and so lock out new write faults during the process of truncation. Because i_mmap_lock is outside the page lock, we can hold it across all the same operations we hold the i_iolock for. The only difference is that we never hold the i_mmaplock in the normal IO path and so do not ever have the possibility that we can page fault inside it. Hence there are no recursion issues on the i_mmap_lock and so we can use it to serialise page fault IO against inode modification operations that affect the IO path. This patch introduces the i_mmaplock infrastructure, lockdep annotations and initialisation/destruction code. Use of the new lock will be in subsequent patches. Signed-off-by: Dave Chinner Reviewed-by: Brian Foster Signed-off-by: Dave Chinner --- fs/xfs/xfs_super.c | 2 ++ 1 file changed, 2 insertions(+) (limited to 'fs/xfs/xfs_super.c') diff --git a/fs/xfs/xfs_super.c b/fs/xfs/xfs_super.c index 8fcc4ccc5c79..50c6fd3bd362 100644 --- a/fs/xfs/xfs_super.c +++ b/fs/xfs/xfs_super.c @@ -986,6 +986,8 @@ xfs_fs_inode_init_once( atomic_set(&ip->i_pincount, 0); spin_lock_init(&ip->i_flags_lock); + mrlock_init(&ip->i_mmaplock, MRLOCK_ALLOW_EQUAL_PRI|MRLOCK_BARRIER, + "xfsino", ip->i_ino); mrlock_init(&ip->i_lock, MRLOCK_ALLOW_EQUAL_PRI|MRLOCK_BARRIER, "xfsino", ip->i_ino); } -- cgit v1.2.3