xfs: don't stall cowblocks scan if we can't take locks

Don't stall the cowblocks scan on a locked inode if we possibly can.
We'd much rather the background scanner keep moving.
Signed-off-by: Darrick J. Wong <djwong@kernel.org>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Brian Foster <bfoster@redhat.com>

fs/xfs/xfs_icache.c

@@ -1605,17 +1605,31 @@ xfs_inode_free_cowblocks(
 	void			*args)
 {
 	struct xfs_eofblocks	*eofb = args;
+	bool			wait;
 	int			ret = 0;
 
+	wait = eofb && (eofb->eof_flags & XFS_EOF_FLAGS_SYNC);
+
 	if (!xfs_prep_free_cowblocks(ip))
 		return 0;
 
 	if (!xfs_inode_matches_eofb(ip, eofb))
 		return 0;
 
-	/* Free the CoW blocks */
-	xfs_ilock(ip, XFS_IOLOCK_EXCL);
-	xfs_ilock(ip, XFS_MMAPLOCK_EXCL);
+	/*
+	 * If the caller is waiting, return -EAGAIN to keep the background
+	 * scanner moving and revisit the inode in a subsequent pass.
+	 */
+	if (!xfs_ilock_nowait(ip, XFS_IOLOCK_EXCL)) {
+		if (wait)
+			return -EAGAIN;
+		return 0;
+	}
+	if (!xfs_ilock_nowait(ip, XFS_MMAPLOCK_EXCL)) {
+		if (wait)
+			ret = -EAGAIN;
+		goto out_iolock;
+	}
 
 	/*
 	 * Check again, nobody else should be able to dirty blocks or change
@@ -1625,6 +1639,7 @@ xfs_inode_free_cowblocks(
 		ret = xfs_reflink_cancel_cow_range(ip, 0, NULLFILEOFF, false);
 
 	xfs_iunlock(ip, XFS_MMAPLOCK_EXCL);
+out_iolock:
 	xfs_iunlock(ip, XFS_IOLOCK_EXCL);
 
 	return ret;