xfs: fix 32-bit truncation in xfs_compute_rextslog

Source kernel commit: cf8f0e6c1429be7652869059ea44696b72d5b726

It's quite reasonable that some customer somewhere will want to
configure a realtime volume with more than 2^32 extents.  If they try to
do this, the highbit32() call will truncate the upper bits of the
xfs_rtbxlen_t and produce the wrong value for rextslog.  This in turn
causes the rsumlevels to be wrong, which results in a realtime summary
file that is the wrong length.  Fix that.

Signed-off-by: Darrick J. Wong <djwong@kernel.org>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Bill O'Donnell <bodonnel@redhat.com>

diff --git a/libxfs/xfs_rtbitmap.c b/libxfs/xfs_rtbitmap.c
index 90fe9028887ae164f0a6712ff471658ca1db3c9f..726543abb51a78dc772cb25ac0e09ea5c42f5bb0 100644 (file)
--- a/libxfs/xfs_rtbitmap.c
+++ b/libxfs/xfs_rtbitmap.c
@@ -1130,14 +1130,16 @@ xfs_rtbitmap_blockcount(
 
 /*
  * Compute the maximum level number of the realtime summary file, as defined by
- * mkfs.  The use of highbit32 on a 64-bit quantity is a historic artifact that
- * prohibits correct use of rt volumes with more than 2^32 extents.
+ * mkfs.  The historic use of highbit32 on a 64-bit quantity prohibited correct
+ * use of rt volumes with more than 2^32 extents.
  */
 uint8_t
 xfs_compute_rextslog(
        xfs_rtbxlen_t           rtextents)
 {
-       return rtextents ? xfs_highbit32(rtextents) : 0;
+       if (!rtextents)
+               return 0;
+       return xfs_highbit64(rtextents);
 }
 
 /*