Hi all, While reading through the realtime geometry support code in xfsprogs, I noticed a discrepancy between the sb_rextslog computation used when writing out the superblock during mkfs and the validation code used in xfs_repair. This discrepancy would lead to system failure for a runt rt volume having more than 1 rt block but zero rt extents in length. Most people aren't going to configure a 1M extent size for their 360k rt floppy disk volume, but I did! In the process of studying that code, it occurred to me that there is a second bug in the computation -- the use of highbit32 for a 64-bit value means that the upper 32 bits are not considered in the search for a high bit. This causes the creation of a realtime summary file that is the wrong length. If rextents is a multiple of U32_MAX then this will appear to work fine because highbit32 returns -1 for an input of 0; but for all other cases the rt summary is undersized, leading to failures. Fix the first problem by standardizing the computation with a helper in libxfs; and the second problem by correcting the computation. This will cause any existing rt volumes larger than 2^32 blocks to fail validation but they probably were already crashing anyway. v2: pick up review tags If you're going to start using this code, I strongly recommend pulling from my git trees, which are linked below. This has been lightly tested with fstests. Enjoy! Comments and questions are, as always, welcome. --D kernel git tree: https://git.kernel.org/cgit/linux/kernel/git/djwong/xfs-linux.git/log/?h=fix-rtmount-overflows-6.8 --- fs/xfs/libxfs/xfs_rtbitmap.c | 14 ++++++++++++++ fs/xfs/libxfs/xfs_rtbitmap.h | 16 ++++++++++++++++ fs/xfs/libxfs/xfs_sb.c | 6 ++++-- fs/xfs/xfs_rtalloc.c | 6 ++++-- 4 files changed, 38 insertions(+), 4 deletions(-)
