[PATCH] Fix BLKPREP_KILL

[PATCH] Fix BLKPREP_KILL

From: Jens Axboe <axboe@suse.de>

Samuel Rydh wrote:

If a MODE_SENSE(6) command is sent to an IDE cd using the CDROM_SEND_PACKET
ioctl, then the kernel freezes solidly. To reproduce this, one can take the
SCSI cmd [1a 08 31 00 10 00] and a 16 byte data buffer.

After some bug hunting, I found out that the following is what happens:

- ide-cd recognizes that MODE_SENSE(6) isn't supported and tries
  to abort the request from ide_cdrom_prep_pc by returning BLKPREP_KILL.

- in elv_next_request(), the kill request is handled by
  the following code:

	while (end_that_request_first(rq, 0, rq->nr_sectors))
		;
	end_that_request_last(rq);

The while loop never exits. The end_that_request_first() doesn't do anything
since rq->nr_sectors is 0; it just returns "not-done" after handling those 0
bytes (rq->bio->bi_size is 16).