[PATCH 12/67] xfs: fix 32-bit truncation in xfs_compute_rextslog

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From: "Darrick J. Wong" <djwong@xxxxxxxxxx>

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@xxxxxxxxxx>
Reviewed-by: Christoph Hellwig <hch@xxxxxx>
Signed-off-by: Carlos Maiolino <cem@xxxxxxxxxx>
 libxfs/xfs_rtbitmap.c | 8 +++++---
 1 file changed, 5 insertions(+), 3 deletions(-)

diff --git a/libxfs/xfs_rtbitmap.c b/libxfs/xfs_rtbitmap.c
index 90fe90288..726543abb 100644
--- 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.
 	xfs_rtbxlen_t		rtextents)
-	return rtextents ? xfs_highbit32(rtextents) : 0;
+	if (!rtextents)
+		return 0;
+	return xfs_highbit64(rtextents);

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