rbd: fix copyup completion race
For write/discard obj_requests that involved a copyup method call, the
opcode of the first op is CEPH_OSD_OP_CALL and the ->callback is
rbd_img_obj_copyup_callback(). The latter frees copyup pages, sets
->xferred and delegates to rbd_img_obj_callback(), the "normal" image
object callback, for reporting to block layer and putting refs.
rbd_osd_req_callback() however treats CEPH_OSD_OP_CALL as a trivial op,
which means obj_request is marked done in rbd_osd_trivial_callback(),
*before* ->callback is invoked and rbd_img_obj_copyup_callback() has
a chance to run. Marking obj_request done essentially means giving
rbd_img_obj_callback() a license to end it at any moment, so if another
obj_request from the same img_request is being completed concurrently,
rbd_img_obj_end_request() may very well be called on such prematurally
marked done request:
<obj_request-1/2 reply>
handle_reply()
rbd_osd_req_callback()
rbd_osd_trivial_callback()
rbd_obj_request_complete()
rbd_img_obj_copyup_callback()
rbd_img_obj_callback()
<obj_request-2/2 reply>
handle_reply()
rbd_osd_req_callback()
rbd_osd_trivial_callback()
for_each_obj_request(obj_request->img_request) {
rbd_img_obj_end_request(obj_request-1/2)
rbd_img_obj_end_request(obj_request-2/2) <--
}
Calling rbd_img_obj_end_request() on such a request leads to trouble,
in particular because its ->xfferred is 0. We report 0 to the block
layer with blk_update_request(), get back 1 for "this request has more
data in flight" and then trip on
rbd_assert(more ^ (which == img_request->obj_request_count));
with rhs (which == ...) being 1 because rbd_img_obj_end_request() has
been called for both requests and lhs (more) being 1 because we haven't
got a chance to set ->xfferred in rbd_img_obj_copyup_callback() yet.
To fix this, leverage that rbd wants to call class methods in only two
cases: one is a generic method call wrapper (obj_request is standalone)
and the other is a copyup (obj_request is part of an img_request). So
make a dedicated handler for CEPH_OSD_OP_CALL and directly invoke
rbd_img_obj_copyup_callback() from it if obj_request is part of an
img_request, similar to how CEPH_OSD_OP_READ handler invokes
rbd_img_obj_request_read_callback().
Since rbd_img_obj_copyup_callback() is now being called from the OSD
request callback (only), it is renamed to rbd_osd_copyup_callback().
Cc: Alex Elder <elder@linaro.org>
Cc: stable@vger.kernel.org # 3.10+, needs backporting for < 3.18
Signed-off-by: Ilya Dryomov <idryomov@gmail.com>
Reviewed-by: Alex Elder <elder@linaro.org>
diff --git a/drivers/block/rbd.c b/drivers/block/rbd.c
index d94529d..bc67a93 100644
--- a/drivers/block/rbd.c
+++ b/drivers/block/rbd.c
@@ -523,6 +523,7 @@
# define rbd_assert(expr) ((void) 0)
#endif /* !RBD_DEBUG */
+static void rbd_osd_copyup_callback(struct rbd_obj_request *obj_request);
static int rbd_img_obj_request_submit(struct rbd_obj_request *obj_request);
static void rbd_img_parent_read(struct rbd_obj_request *obj_request);
static void rbd_dev_remove_parent(struct rbd_device *rbd_dev);
@@ -1818,6 +1819,16 @@
obj_request_done_set(obj_request);
}
+static void rbd_osd_call_callback(struct rbd_obj_request *obj_request)
+{
+ dout("%s: obj %p\n", __func__, obj_request);
+
+ if (obj_request_img_data_test(obj_request))
+ rbd_osd_copyup_callback(obj_request);
+ else
+ obj_request_done_set(obj_request);
+}
+
static void rbd_osd_req_callback(struct ceph_osd_request *osd_req,
struct ceph_msg *msg)
{
@@ -1866,6 +1877,8 @@
rbd_osd_discard_callback(obj_request);
break;
case CEPH_OSD_OP_CALL:
+ rbd_osd_call_callback(obj_request);
+ break;
case CEPH_OSD_OP_NOTIFY_ACK:
case CEPH_OSD_OP_WATCH:
rbd_osd_trivial_callback(obj_request);
@@ -2530,13 +2543,15 @@
}
static void
-rbd_img_obj_copyup_callback(struct rbd_obj_request *obj_request)
+rbd_osd_copyup_callback(struct rbd_obj_request *obj_request)
{
struct rbd_img_request *img_request;
struct rbd_device *rbd_dev;
struct page **pages;
u32 page_count;
+ dout("%s: obj %p\n", __func__, obj_request);
+
rbd_assert(obj_request->type == OBJ_REQUEST_BIO ||
obj_request->type == OBJ_REQUEST_NODATA);
rbd_assert(obj_request_img_data_test(obj_request));
@@ -2563,9 +2578,7 @@
if (!obj_request->result)
obj_request->xferred = obj_request->length;
- /* Finish up with the normal image object callback */
-
- rbd_img_obj_callback(obj_request);
+ obj_request_done_set(obj_request);
}
static void
@@ -2650,7 +2663,6 @@
/* All set, send it off. */
- orig_request->callback = rbd_img_obj_copyup_callback;
osdc = &rbd_dev->rbd_client->client->osdc;
img_result = rbd_obj_request_submit(osdc, orig_request);
if (!img_result)