rbd: read image size for discard check safely

In rbd_img_request_fill() the image size is only checked to determine
whether we can truncate an object instead of zeroing it for discard
requests. Take rbd_dev->header_rwsem while reading the image size, and
move this read into the discard check, so that non-discard ops don't
need to take the semaphore in this function.

Signed-off-by: Josh Durgin <josh.durgin@inktank.com>

1 files changed, 12 insertions, 6 deletions

diff --git a/drivers/block/rbd.c b/drivers/block/rbd.c
index e2f7a708e20d..31ace3dd33e4 100644
--- a/drivers/block/rbd.c
+++ b/drivers/block/rbd.c
@@ -2332,7 +2332,6 @@ static int rbd_img_request_fill(struct rbd_img_request *img_request,
                 (int)type, data_desc);
 
         img_offset = img_request->offset;
-        img_end = rbd_dev->header.image_size;
         resid = img_request->length;
         rbd_assert(resid > 0);
 
@@ -2397,13 +2396,20 @@ static int rbd_img_request_fill(struct rbd_img_request *img_request,
                         if (!offset && (length == object_size)
                                 && (!img_request_layered_test(img_request) ||
                                         (rbd_dev->parent_overlap <=
-                                                obj_request->img_offset)))
+                                                obj_request->img_offset))) {
                                 opcode = CEPH_OSD_OP_DELETE;
-                        else if ((offset + length == object_size) ||
-                                (obj_request->img_offset + length == img_end))
+                        } else if ((offset + length == object_size)) {
                                 opcode = CEPH_OSD_OP_TRUNCATE;
-                        else
-                                opcode = CEPH_OSD_OP_ZERO;
+                        } else {
+                                down_read(&rbd_dev->header_rwsem);
+                                img_end = rbd_dev->header.image_size;
+                                up_read(&rbd_dev->header_rwsem);
+
+                                if (obj_request->img_offset + length == img_end)
+                                        opcode = CEPH_OSD_OP_TRUNCATE;
+                                else
+                                        opcode = CEPH_OSD_OP_ZERO;
+                        }
                 } else if (img_request_write_test(img_request)) {
                         op_type = OBJ_OP_WRITE;
                         opcode = CEPH_OSD_OP_WRITE;