Dmitry Monakhov wrote:

->s_group_desc have to be zero filled because if sb_read() failed
we jump to following error path.
failed_mount2:
	for (i = 0; i < db_count; i++)
		brelse(sbi->s_group_desc[i]);<< Bad things may happen here

But the db_count is updated in the failure path to point to the number
of successful sb_read. 

-aneesh