xfs: don't take the MMAPLOCK when scrubbing file metadata

The MMAPLOCK stabilizes mappings in a file's pagecache.  Therefore, we
do not need it to check directories, symlinks, extended attributes, or
file-based metadata.  Reduce its usage to the one case that requires it,
which is when we want to scrub the data fork of a regular file.

Signed-off-by: Darrick J. Wong <djwong@kernel.org>
Reviewed-by: Dave Chinner <dchinner@redhat.com>

Author: Darrick J. Wong

fs/xfs/scrub/bmap.c

@@ -38,8 +38,8 @@ xchk_setup_inode_bmap(
 	if (error)
 		goto out;
 
-	sc->ilock_flags = XFS_IOLOCK_EXCL | XFS_MMAPLOCK_EXCL;
-	xfs_ilock(sc->ip, sc->ilock_flags);
+	sc->ilock_flags = XFS_IOLOCK_EXCL;
+	xfs_ilock(sc->ip, XFS_IOLOCK_EXCL);
 
 	/*
 	 * We don't want any ephemeral data fork updates sitting around
@@ -50,6 +50,9 @@ xchk_setup_inode_bmap(
 	    sc->sm->sm_type == XFS_SCRUB_TYPE_BMBTD) {
 		struct address_space	*mapping = VFS_I(sc->ip)->i_mapping;
 
+		sc->ilock_flags |= XFS_MMAPLOCK_EXCL;
+		xfs_ilock(sc->ip, XFS_MMAPLOCK_EXCL);
+
 		inode_dio_wait(VFS_I(sc->ip));
 
 		/*

fs/xfs/scrub/common.c

@@ -988,7 +988,11 @@ xchk_irele(
 	xfs_irele(ip);
 }
 
-/* Set us up to scrub a file's contents. */
+/*
+ * Set us up to scrub metadata mapped by a file's fork.  Callers must not use
+ * this to operate on user-accessible regular file data because the MMAPLOCK is
+ * not taken.
+ */
 int
 xchk_setup_inode_contents(
 	struct xfs_scrub	*sc,
@@ -1000,9 +1004,10 @@ xchk_setup_inode_contents(
 	if (error)
 		return error;
 
-	/* Got the inode, lock it and we're ready to go. */
-	sc->ilock_flags = XFS_IOLOCK_EXCL | XFS_MMAPLOCK_EXCL;
+	/* Lock the inode so the VFS cannot touch this file. */
+	sc->ilock_flags = XFS_IOLOCK_EXCL;
 	xfs_ilock(sc->ip, sc->ilock_flags);
+
 	error = xchk_trans_alloc(sc, resblks);
 	if (error)
 		goto out;

fs/xfs/scrub/inode.c

@@ -32,7 +32,7 @@ xchk_prepare_iscrub(
 {
 	int			error;
 
-	sc->ilock_flags = XFS_IOLOCK_EXCL | XFS_MMAPLOCK_EXCL;
+	sc->ilock_flags = XFS_IOLOCK_EXCL;
 	xfs_ilock(sc->ip, sc->ilock_flags);
 
 	error = xchk_trans_alloc(sc, 0);