xfs: truncate transaction does not modify the inobt

[ Upstream commit a606ebdb ]

The truncate transaction does not ever modify the inode btree, but
includes an associated log reservation. Update
xfs_calc_itruncate_reservation() to remove the reservation
associated with inobt updates.

[Amir:	This commit was merged for kernel v4.16 and a twin commit was
	merged for xfsprogs v4.16. As a result, a small xfs filesystem
	formatted with features -m rmapbt=1,reflink=1 using mkfs.xfs
	version >= v4.16 cannot be mounted with kernel < v4.16.

	For example, xfstests generic/17{1,2,3} format a small fs and
	when trying to mount it, they fail with an assert on this very
	demonic line:

 XFS (vdc): Log size 3075 blocks too small, minimum size is 3717 blocks
 XFS (vdc): AAIEEE! Log failed size checks. Abort!
 XFS: Assertion failed: 0, file: src/linux/fs/xfs/xfs_log.c, line: 666

	The simple solution for stable kernels is to apply this patch,
	because mkfs.xfs v4.16 is already in the wild, so we have to
	assume that xfs filesystems with a "too small" log exist.
	Regardless, xfsprogs maintainers should also consider reverting
	the twin patch to stop creating those filesystems for the sake
	of users with unpatched kernels.]
Signed-off-by: Brian Foster <bfoster@redhat.com>
Reviewed-by: Dave Chinner <dchinner@redhat.com>
Reviewed-by: Darrick J. Wong <darrick.wong@oracle.com>
Signed-off-by: Darrick J. Wong <darrick.wong@oracle.com>
Cc: <stable@vger.kernel.org> # v4.9+
Signed-off-by: Amir Goldstein <amir73il@gmail.com>
Reviewed-by: Darrick J . Wong <darrick.wong@oracle.com>
Signed-off-by: Sasha Levin <sashal@kernel.org>

fs/xfs/libxfs/xfs_trans_resv.c

@@ -232,8 +232,6 @@ xfs_calc_write_reservation(
  *    the super block to reflect the freed blocks: sector size
  *    worst case split in allocation btrees per extent assuming 4 extents:
  *		4 exts * 2 trees * (2 * max depth - 1) * block size
- *    the inode btree: max depth * blocksize
- *    the allocation btrees: 2 trees * (max depth - 1) * block size
  */
 STATIC uint
 xfs_calc_itruncate_reservation(
@@ -245,12 +243,7 @@ xfs_calc_itruncate_reservation(
 				      XFS_FSB_TO_B(mp, 1))),
 		    (xfs_calc_buf_res(9, mp->m_sb.sb_sectsize) +
 		     xfs_calc_buf_res(xfs_allocfree_log_count(mp, 4),
-				      XFS_FSB_TO_B(mp, 1)) +
-		    xfs_calc_buf_res(5, 0) +
-		    xfs_calc_buf_res(xfs_allocfree_log_count(mp, 1),
-				     XFS_FSB_TO_B(mp, 1)) +
-		    xfs_calc_buf_res(2 + mp->m_ialloc_blks +
-				     mp->m_in_maxlevels, 0)));
+				      XFS_FSB_TO_B(mp, 1))));
 }
 
 /*