block: WARN in __blk_put_request() for potential bio leak

Put a WARN_ON in __blk_put_request if it is about to
leak bio(s). This is a serious bug that can happen in error
handling code paths.

For this to work I have fixed a couple of places in block/ where
request->bio != NULL ownership was not honored. And a small cleanup
at sg_io() while at it.

Signed-off-by: Boaz Harrosh <bharrosh@panasas.com>
Signed-off-by: Jens Axboe <jens.axboe@oracle.com>

block/blk-core.c

@@ -1062,6 +1062,9 @@ void __blk_put_request(struct request_queue *q, struct request *req)
 
 	elv_completed_request(q, req);
 
+	/* this is a bio leak */
+	WARN_ON(req->bio != NULL);
+
 	/*
 	 * Request may not have originated from ll_rw_blk. if not,
 	 * it didn't come out of our reserved rq pools

block/blk-merge.c

@@ -403,6 +403,8 @@ static int attempt_merge(struct request_queue *q, struct request *req,
 	if (blk_rq_cpu_valid(next))
 		req->cpu = next->cpu;
 
+	/* owner-ship of bio passed from next to req */
+	next->bio = NULL;
 	__blk_put_request(q, next);
 	return 1;
 }

block/scsi_ioctl.c

@@ -214,21 +214,10 @@ static int blk_fill_sghdr_rq(struct request_queue *q, struct request *rq,
 	return 0;
 }
 
-/*
- * unmap a request that was previously mapped to this sg_io_hdr. handles
- * both sg and non-sg sg_io_hdr.
- */
-static int blk_unmap_sghdr_rq(struct request *rq, struct sg_io_hdr *hdr)
-{
-	blk_rq_unmap_user(rq->bio);
-	blk_put_request(rq);
-	return 0;
-}
-
 static int blk_complete_sghdr_rq(struct request *rq, struct sg_io_hdr *hdr,
 				 struct bio *bio)
 {
-	int r, ret = 0;
+	int ret = 0;
 
 	/*
 	 * fill in all the output members
@@ -253,12 +242,10 @@ static int blk_complete_sghdr_rq(struct request *rq, struct sg_io_hdr *hdr,
 			ret = -EFAULT;
 	}
 
-	rq->bio = bio;
-	r = blk_unmap_sghdr_rq(rq, hdr);
-	if (ret)
-		r = ret;
+	blk_rq_unmap_user(bio);
+	blk_put_request(rq);
 
-	return r;
+	return ret;
 }
 
 static int sg_io(struct request_queue *q, struct gendisk *bd_disk,