rbd: decrement obj request count when deleting

Decrement the obj_request_count value when deleting an object
request from its image request's list.  Rearrange a few lines
in the surrounding code.

This resolves:
    http://tracker.ceph.com/issues/3940

Signed-off-by: Alex Elder <elder@inktank.com>
Reviewed-by: Josh Durgin <josh.durgin@inktank.com>

1 files changed, 12 insertions, 4 deletions

diff --git a/drivers/block/rbd.c b/drivers/block/rbd.c
index fc1a045cee4d..d3d15d06abc0 100644
--- a/drivers/block/rbd.c
+++ b/drivers/block/rbd.c
@@ -1063,22 +1063,29 @@ static void rbd_img_request_put(struct rbd_img_request *img_request)
 static inline void rbd_img_obj_request_add(struct rbd_img_request *img_request,
                                         struct rbd_obj_request *obj_request)
 {
+        rbd_assert(obj_request->img_request == NULL);
+
         rbd_obj_request_get(obj_request);
         obj_request->img_request = img_request;
-        list_add_tail(&obj_request->links, &img_request->obj_requests);
-        obj_request->which = img_request->obj_request_count++;
+        obj_request->which = img_request->obj_request_count;
         rbd_assert(obj_request->which != BAD_WHICH);
+        img_request->obj_request_count++;
+        list_add_tail(&obj_request->links, &img_request->obj_requests);
 }
 
 static inline void rbd_img_obj_request_del(struct rbd_img_request *img_request,
                                         struct rbd_obj_request *obj_request)
 {
         rbd_assert(obj_request->which != BAD_WHICH);
-        obj_request->which = BAD_WHICH;
+
         list_del(&obj_request->links);
+        rbd_assert(img_request->obj_request_count > 0);
+        img_request->obj_request_count--;
+        rbd_assert(obj_request->which == img_request->obj_request_count);
+        obj_request->which = BAD_WHICH;
         rbd_assert(obj_request->img_request == img_request);
-        obj_request->callback = NULL;
         obj_request->img_request = NULL;
+        obj_request->callback = NULL;
         rbd_obj_request_put(obj_request);
 }
 
@@ -1472,6 +1479,7 @@ static void rbd_img_request_destroy(struct kref *kref)
 
         for_each_obj_request_safe(img_request, obj_request, next_obj_request)
                 rbd_img_obj_request_del(img_request, obj_request);
+        rbd_assert(img_request->obj_request_count == 0);
 
         if (img_request->write_request)
                 ceph_put_snap_context(img_request->snapc);