Hi!
> tst_test.c:1161: INFO: Testing on vfat
> tst_mkfs.c:90: INFO: Formatting /dev/loop0 with vfat opts='' extra opts=''
> mkfs.vfat: unable to open /dev/loop0: Device or resource busy
> tst_mkfs.c:101: BROK: mkfs.vfat:1: tst_test.c failed with 741

This looks like mkfs.vfat got EBUSY after the loop device was
succesfully umounted.

We do run the test in a loop for several filesystems and the loop
generally does:

next:
	mkfs
	mount
	test
	umount
	goto next;

-- 
Cyril Hrubis
chrubis@suse.cz