Merge tag 'xfs-4.17-fixes-2' of git://git.kernel.org/pub/scm/fs/xfs/xfs-linux

Pull xfs fixes from Darrick Wong:
 "I've got one more bug fix for xfs for 4.17-rc4, which caps the amount
  of data we try to handle in one dedupe request so that userspace can't
  livelock the kernel.

  This series has been run through a full xfstests run during the week
  and through a quick xfstests run against this morning's master, with
  no ajor failures reported.

  Summary:

  - Cap the maximum length of a deduplication request at MAX_RW_COUNT/2
    to avoid kernel livelock due to excessively large IO requests"

* tag 'xfs-4.17-fixes-2' of git://git.kernel.org/pub/scm/fs/xfs/xfs-linux:
  xfs: cap the length of deduplication requests

fs/xfs/xfs_file.c

@@ -880,8 +880,18 @@ xfs_file_dedupe_range(
 	struct file	*dst_file,
 	u64		dst_loff)
 {
+	struct inode	*srci = file_inode(src_file);
+	u64		max_dedupe;
 	int		error;
 
+	/*
+	 * Since we have to read all these pages in to compare them, cut
+	 * it off at MAX_RW_COUNT/2 rounded down to the nearest block.
+	 * That means we won't do more than MAX_RW_COUNT IO per request.
+	 */
+	max_dedupe = (MAX_RW_COUNT >> 1) & ~(i_blocksize(srci) - 1);
+	if (len > max_dedupe)
+		len = max_dedupe;
 	error = xfs_reflink_remap_range(src_file, loff, dst_file, dst_loff,
 				     len, true);
 	if (error)