xfs: prevent metadata files from being inactivated

Files containing metadata (quota records, rt bitmap and summary info)
are fully managed by the filesystem, which means that all resource
cleanup must be explicit, not automatic. This means that they should
never be subjected automatic to post-eof truncation, nor should they be
freed automatically even if the link count drops to zero.

In other words, xfs_inactive() should leave these files alone. Add the
necessary predicate functions to make this happen. This adds a second
layer of prevention for the kinds of fs corruption that was fixed by
commit f4c32e87de7d. If we ever decide to support removing metadata
files, we should make all those metadata updates explicit.

Rearrange the order of #includes to fix compiler errors, since
xfs_mount.h is supposed to be included before xfs_inode.h

Followup-to: f4c32e87de7d ("xfs: fix realtime bitmap/summary file truncation when growing rt volume")
Signed-off-by: Darrick J. Wong <[e-mail]>
Reviewed-by: Christoph Hellwig <[e-mail]>

fs/xfs/libxfs/xfs_iext_tree.c

···
 #include "xfs_format.h"
 #include "xfs_bit.h"
 #include "xfs_log_format.h"
-#include "xfs_inode.h"
 #include "xfs_trans_resv.h"
 #include "xfs_mount.h"
+#include "xfs_inode.h"
 #include "xfs_trace.h"
 
 /*

fs/xfs/xfs_inode.c

···
 	if (mp->m_flags & XFS_MOUNT_RDONLY)
 		return;
 
+	/* Metadata inodes require explicit resource cleanup. */
+	if (xfs_is_metadata_inode(ip))
+		return;
+
 	/* Try to clean out the cow blocks if there are any. */
 	if (xfs_inode_has_cow_data(ip))
 		xfs_reflink_cancel_cow_range(ip, 0, NULLFILEOFF, true);

fs/xfs/xfs_inode.h

···
 	return ip->i_d.di_flags2 & XFS_DIFLAG2_REFLINK;
 }
 
+static inline bool xfs_is_metadata_inode(struct xfs_inode *ip)
+{
+	struct xfs_mount	*mp = ip->i_mount;
+
+	return ip == mp->m_rbmip || ip == mp->m_rsumip ||
+		xfs_is_quota_inode(&mp->m_sb, ip->i_ino);
+}
+
 /*
  * Check if an inode has any data in the COW fork.  This might be often false
  * even for inodes with the reflink flag when there is no pending COW operation.

fs/xfs/xfs_xattr.c

···
 #include "xfs_format.h"
 #include "xfs_log_format.h"
 #include "xfs_da_format.h"
+#include "xfs_trans_resv.h"
+#include "xfs_mount.h"
 #include "xfs_inode.h"
 #include "xfs_attr.h"
 #include "xfs_acl.h"