From 67be29011d7db2985d1c1f57474932d20705dab7 Mon Sep 17 00:00:00 2001
From: Dave Chinner <dchinner@redhat.com>
Date: Tue, 13 Jul 2010 17:50:50 +1000
Subject: [PATCH] --- yaml --- r: 208271 b: refs/heads/master c:
 f10d9f617a65905c556c3b37c9b9646ae7d04ed7 h: refs/heads/master i:   208269:
 815e2c84d8def140dffdb74011fded5dd9c5720c   208267:
 b49e44d764630c856100e39ec758f56d3d5788b9   208263:
 ae77c21a92af1b70f381bc5a50cb0e18e0dcc711   208255:
 5a6b796dd32a947fbe521c109bb62ae7620884ba v: v3

---
 [refs]                    | 2 +-
 trunk/block/blk-barrier.c | 9 +++++++++
 2 files changed, 10 insertions(+), 1 deletion(-)

diff --git a/[refs] b/[refs]
index 51fa7f6fd71d..d091c75ce561 100644
--- a/[refs]
+++ b/[refs]
@@ -1,2 +1,2 @@
 ---
-refs/heads/master: 2669b19fa4debcdd6a660ace1a124c0900f113e6
+refs/heads/master: f10d9f617a65905c556c3b37c9b9646ae7d04ed7
diff --git a/trunk/block/blk-barrier.c b/trunk/block/blk-barrier.c
index eefbde835308..557f69360b6a 100644
--- a/trunk/block/blk-barrier.c
+++ b/trunk/block/blk-barrier.c
@@ -310,6 +310,15 @@ int blkdev_issue_flush(struct block_device *bdev, gfp_t gfp_mask,
 	if (!q)
 		return -ENXIO;
 
+	/*
+	 * some block devices may not have their queue correctly set up here
+	 * (e.g. loop device without a backing file) and so issuing a flush
+	 * here will panic. Ensure there is a request function before issuing
+	 * the barrier.
+	 */
+	if (!q->make_request_fn)
+		return -ENXIO;
+
 	bio = bio_alloc(gfp_mask, 0);
 	bio->bi_end_io = bio_end_empty_barrier;
 	bio->bi_bdev = bdev;