[PATCH v2] virtio_blk: fix defaults for max_hw_sectors and max_segment_size

[Mike Snitzer <snitzer@redhat.com>]

virtio_blk incorrectly established -1U as the default for these
queue_limits.  Set these limits to sane default values to avoid crashing
the kernel.  But the virtio-blk protocol should probably be extended to
allow proper stacking of the disk's limits from the host.

This change fixes a crash that can occur if the max_sectors_kb is
modified to even be half of virtio_blk's advertised max_hw_sectors_kb:

  # cat /sys/block/vdb/queue/max_sectors_kb
  512
  # cat /sys/block/vdb/queue/max_hw_sectors_kb
  2147483647
  # echo 1073741824 > /sys/block/vdb/queue/max_sectors_kb

Attempting to mkfs.xfs against /dev/vdb will result in hitting
fs/direct-io.c:dio_send_cur_page()'s BUG_ON.

While fixing the blk_queue_max_hw_sectors(q, -1U) call it was
immediately apparent that the blk_queue_max_segment_size(q, -1U) also
should be fixed.

Signed-off-by: Mike Snitzer <snitzer@redhat.com>
Cc: stable@vger.kernel.org
---
 drivers/block/virtio_blk.c |    9 ++++++---
 1 files changed, 6 insertions(+), 3 deletions(-)

v2: revise header to simplify the scope of the problem explanation

diff --git a/drivers/block/virtio_blk.c b/drivers/block/virtio_blk.c
index c6a27d5..68efbdc 100644
--- a/drivers/block/virtio_blk.c
+++ b/drivers/block/virtio_blk.c
@@ -674,8 +674,11 @@ static int virtblk_probe(struct virtio_device *vdev)
 	/* No need to bounce any requests */
 	blk_queue_bounce_limit(q, BLK_BOUNCE_ANY);
 
-	/* No real sector limit. */
-	blk_queue_max_hw_sectors(q, -1U);
+	/*
+	 * Limited by disk's max_hw_sectors in host, but
+	 * without that info establish a sane default.
+	 */
+	blk_queue_max_hw_sectors(q, BLK_DEF_MAX_SECTORS);
 
 	/* Host can optionally specify maximum segment size and number of
 	 * segments. */
@@ -684,7 +687,7 @@ static int virtblk_probe(struct virtio_device *vdev)
 	if (!err)
 		blk_queue_max_segment_size(q, v);
 	else
-		blk_queue_max_segment_size(q, -1U);
+		blk_queue_max_segment_size(q, BLK_MAX_SEGMENT_SIZE);
 
 	/* Host can optionally specify the block size of the device */
 	err = virtio_cread_feature(vdev, VIRTIO_BLK_F_BLK_SIZE,
-- 
1.7.4.4