releases/2.6.31.1/block-don-t-assume-device-has-a-request-list-backing-in-nr_requests-store.patch

From b8a9ae779f2c7049071034661e09cb7e1e82250c Mon Sep 17 00:00:00 2001
From: Jens Axboe <jens.axboe@oracle.com>
Date: Fri, 11 Sep 2009 22:44:29 +0200
Subject: block: don't assume device has a request list backing in nr_requests store

From: Jens Axboe <jens.axboe@oracle.com>

commit b8a9ae779f2c7049071034661e09cb7e1e82250c upstream.

Stacked devices do not. For now, just error out with -EINVAL. Later
we could make the limit apply on stacked devices too, for throttling
reasons.

This fixes

5a54cd13353bb3b88887604e2c980aa01e314309

and should go into 2.6.31 stable as well.

Signed-off-by: Jens Axboe <jens.axboe@oracle.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>

---
 block/blk-sysfs.c |    7 ++++++-
 1 file changed, 6 insertions(+), 1 deletion(-)

--- a/block/blk-sysfs.c
+++ b/block/blk-sysfs.c
@@ -40,7 +40,12 @@ queue_requests_store(struct request_queu
 {
 	struct request_list *rl = &q->rq;
 	unsigned long nr;
-	int ret = queue_var_store(&nr, page, count);
+	int ret;
+
+	if (!q->request_fn)
+		return -EINVAL;
+
+	ret = queue_var_store(&nr, page, count);
 	if (nr < BLKDEV_MIN_RQ)
 		nr = BLKDEV_MIN_RQ;