Fix request-notification holdoff in blkback. New code is

more correct and clearer in intent.

Signed-off-by: Keir Fraser <keir@xensource.com>

diff --git a/linux-2.6-xen-sparse/drivers/xen/blkback/blkback.c b/linux-2.6-xen-sparse/drivers/xen/blkback/blkback.c
index f689dd0662ffbf7ca6469cd5e159621a91de72fa..fcc6c12de4d8b57aa33d83bf5f5751c3fec3ae9c 100644 (file)
--- a/linux-2.6-xen-sparse/drivers/xen/blkback/blkback.c
+++ b/linux-2.6-xen-sparse/drivers/xen/blkback/blkback.c
@@ -483,23 +483,22 @@ static void make_response(blkif_t *blkif, unsigned long id,
        blkif_back_ring_t *blk_ring = &blkif->blk_ring;
        int notify;
 
-       /* Place on the response ring for the relevant domain. */ 
        spin_lock_irqsave(&blkif->blk_ring_lock, flags);
+
+       /* Place on the response ring for the relevant domain. */ 
        resp = RING_GET_RESPONSE(blk_ring, blk_ring->rsp_prod_pvt);
        resp->id        = id;
        resp->operation = op;
        resp->status    = st;
        blk_ring->rsp_prod_pvt++;
        RING_PUSH_RESPONSES_AND_CHECK_NOTIFY(blk_ring, notify);
-       spin_unlock_irqrestore(&blkif->blk_ring_lock, flags);
 
        /*
          * Tail check for pending requests. Allows frontend to avoid
          * notifications if requests are already in flight (lower overheads
          * and promotes batching).
          */
-       mb();
-       if (!__on_blkdev_list(blkif)) {
+       if (blk_ring->rsp_prod_pvt == blk_ring->req_cons) {
                int more_to_do;
                RING_FINAL_CHECK_FOR_REQUESTS(blk_ring, more_to_do);
                if (more_to_do) {
@@ -508,6 +507,8 @@ static void make_response(blkif_t *blkif, unsigned long id,
                }
        }
 
+       spin_unlock_irqrestore(&blkif->blk_ring_lock, flags);
+
        if (notify)
                notify_remote_via_irq(blkif->irq);
 }