Just curious - bio.c query

[utzoo!decvax!duke!chico!harpo!floyd!cmcl2!salkind]

In both physio() and swap(), the test

	if (bp->b_flags&B_WANTED)
		wakeup((caddr_t)bp);

runs at spl6().  Why does it have to run at spl6()?  In brelse() and
iodone() the same test does not run at spl6().

					Thanks in advance,
					Lou Salkind