dm integrity: WARN_ON if variables representing journal usage get out of sync

If this WARN_ON triggers it speaks to programmer error, and likely
implies corruption, but no released kernel should trigger it.  This
WARN_ON serves to assist DM integrity developers as changes are
made/tested in the future.

BUG_ON is excessive for catching programmer error, if a user or
developer would like warnings to trigger a panic, they can enable that
via /proc/sys/kernel/panic_on_warn
Signed-off-by: Mikulas Patocka <mpatocka@redhat.com>
Signed-off-by: Mike Snitzer <snitzer@redhat.com>

drivers/md/dm-integrity.c

@@ -1729,6 +1729,8 @@ static void pad_uncommitted(struct dm_integrity_c *ic)
 		wraparound_section(ic, &ic->free_section);
 		ic->n_uncommitted_sections++;
 	}
+	WARN_ON(ic->journal_sections * ic->journal_section_entries !=
+		(ic->n_uncommitted_sections + ic->n_committed_sections) * ic->journal_section_entries + ic->free_sectors);
 }
 
 static void integrity_commit(struct work_struct *w)