[PATCH block#for-2.6.31] block: fix an oops on BLKPREP_KILL

[James Bottomley <James.Bottomley@HansenPartnership.com>]

Doing a bit of torture testing, I ran across a BUG in the block
subsystem (at blk-core.c:2048): the test for if the request is queued.

It turns out the trigger was a BLKPREP_KILL coming out of the SCSI prep
function.  Currently for BLKPREP_KILL requests, we send them straight
into __blk_end_request_all() with an error, but they've never been
dequeued, so they trip the bug.  Fix this by starting requests before
killing them.

Signed-off-by: James Bottomley <James.Bottomley@HansenPartnership.com>

---

diff --git a/block/blk-core.c b/block/blk-core.c
index 8b3b74e..9a0568c 100644
--- a/block/blk-core.c
+++ b/block/blk-core.c
@@ -1789,6 +1789,7 @@ struct request *blk_peek_request(struct request_queue *q)
 			break;
 		} else if (ret == BLKPREP_KILL) {
 			rq->cmd_flags |= REQ_QUIET;
+			blk_start_request(rq);
 			__blk_end_request_all(rq, -EIO);
 		} else {
 			printk(KERN_ERR "%s: bad return=%d\n", __func__, ret);