block: don't assume device has a request list backing in nr_requests store

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.

Cc: stable@kernel.org
Signed-off-by: Jens Axboe <jens.axboe@oracle.com>

1 files changed, 6 insertions, 1 deletions

diff --git a/block/blk-sysfs.c b/block/blk-sysfs.c
index d3aa2aadb3e0..b78c9c3e2670 100644
--- a/block/blk-sysfs.c
+++ b/block/blk-sysfs.c
@@ -40,7 +40,12 @@ queue_requests_store(struct request_queue *q, const char *page, size_t count)
 {
         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;