xfs: check min blks for random debug mode sparse allocations

The inode allocator enables random sparse inode chunk allocations in
DEBUG mode to facilitate testing. Sparse inode allocations are not
always possible, however, depending on the fs geometry. For example,
there is no possibility for a sparse inode allocation on filesystems
where the block size is large enough to fit one or more inode chunks
within a single block.

Fix up the DEBUG mode sparse inode allocation logic to trigger random
sparse allocations only when the geometry of the fs allows it.

Signed-off-by: Brian Foster <bfoster@redhat.com>
Reviewed-by: Dave Chinner <dchinner@redhat.com>
Signed-off-by: Dave Chinner <david@fromorbit.com>

fs/xfs/libxfs/xfs_ialloc.c

@@ -606,20 +606,20 @@ xfs_ialloc_ag_alloc(
 	uint16_t	allocmask = (uint16_t) -1; /* init. to full chunk */
 	struct xfs_inobt_rec_incore rec;
 	struct xfs_perag *pag;
-
 	int		do_sparse = 0;
 
-#ifdef DEBUG
-	/* randomly do sparse inode allocations */
-	if (xfs_sb_version_hassparseinodes(&tp->t_mountp->m_sb))
-		do_sparse = prandom_u32() & 1;
-#endif
-
 	memset(&args, 0, sizeof(args));
 	args.tp = tp;
 	args.mp = tp->t_mountp;
 	args.fsbno = NULLFSBLOCK;
 
+#ifdef DEBUG
+	/* randomly do sparse inode allocations */
+	if (xfs_sb_version_hassparseinodes(&tp->t_mountp->m_sb) &&
+	    args.mp->m_ialloc_min_blks < args.mp->m_ialloc_blks)
+		do_sparse = prandom_u32() & 1;
+#endif
+
 	/*
 	 * Locking will ensure that we don't have two callers in here
 	 * at one time.
@@ -768,6 +768,7 @@ xfs_ialloc_ag_alloc(
 			return error;
 
 		newlen = args.len << args.mp->m_sb.sb_inopblog;
+		ASSERT(newlen <= XFS_INODES_PER_CHUNK);
 		allocmask = (1 << (newlen / XFS_INODES_PER_HOLEMASK_BIT)) - 1;
 	}