[PATCH 11/15] rbd: drop state_mutex in __rbd_img_handle_request()

[Hannes Reinecke <hare@xxxxxxx>]

The use of READ_ONCE/WRITE_ONCE for the image request state allows
us to drop the state_mutex in __rbd_img_handle_request().

Signed-off-by: Hannes Reinecke <hare@xxxxxxx>
---
 drivers/block/rbd.c | 26 +++++++++-----------------
 1 file changed, 9 insertions(+), 17 deletions(-)

diff --git a/drivers/block/rbd.c b/drivers/block/rbd.c
index 671e941d6edf..db04401c4d8b 100644
--- a/drivers/block/rbd.c
+++ b/drivers/block/rbd.c
@@ -349,7 +349,6 @@ struct rbd_img_request {
 	struct list_head	object_extents;	/* obj_req.ex structs */
 	struct mutex		object_mutex;
 
-	struct mutex		state_mutex;
 	int			pending_result;
 	struct work_struct	work;
 	struct kref		kref;
@@ -1674,7 +1673,6 @@ static struct rbd_img_request *rbd_img_request_create(
 
 	INIT_LIST_HEAD(&img_request->lock_item);
 	INIT_LIST_HEAD(&img_request->object_extents);
-	mutex_init(&img_request->state_mutex);
 	mutex_init(&img_request->object_mutex);
 	kref_init(&img_request->kref);
 
@@ -2529,7 +2527,7 @@ static int __rbd_img_fill_request(struct rbd_img_request *img_req)
 		}
 	}
 	mutex_unlock(&img_req->object_mutex);
-	img_req->state = RBD_IMG_START;
+	WRITE_ONCE(img_req->state, RBD_IMG_START);
 	return 0;
 }
 
@@ -3652,15 +3650,15 @@ static bool rbd_img_advance(struct rbd_img_request *img_req, int *result)
 	int ret;
 
 	dout("%s: img %p state %d\n", __func__, img_req, img_req->state);
-	switch (img_req->state) {
+	switch (READ_ONCE(img_req->state)) {
 	case RBD_IMG_START:
 		rbd_assert(!*result);
 
-		img_req->state = RBD_IMG_EXCLUSIVE_LOCK;
+		WRITE_ONCE(img_req->state, RBD_IMG_EXCLUSIVE_LOCK);
 		ret = rbd_img_exclusive_lock(img_req);
 		if (ret < 0) {
 			*result = ret;
-			img_req->state = RBD_IMG_DONE;
+			WRITE_ONCE(img_req->state, RBD_IMG_DONE);
 			return true;
 		}
 		if (ret == 0)
@@ -3668,17 +3666,17 @@ static bool rbd_img_advance(struct rbd_img_request *img_req, int *result)
 		/* fall through */
 	case RBD_IMG_EXCLUSIVE_LOCK:
 		if (*result) {
-			img_req->state = RBD_IMG_DONE;
+			WRITE_ONCE(img_req->state, RBD_IMG_DONE);
 			return true;
 		}
 
 		rbd_assert(!need_exclusive_lock(img_req) ||
 			   __rbd_is_lock_owner(rbd_dev));
 
-		img_req->state = RBD_IMG_OBJECT_REQUESTS;
+		WRITE_ONCE(img_req->state, RBD_IMG_OBJECT_REQUESTS);
 		if (!rbd_img_object_requests(img_req)) {
 			*result = img_req->pending_result;
-			img_req->state = RBD_IMG_DONE;
+			WRITE_ONCE(img_req->state, RBD_IMG_DONE);
 			return true;
 		}
 		return false;
@@ -3686,7 +3684,7 @@ static bool rbd_img_advance(struct rbd_img_request *img_req, int *result)
 		if (rbd_img_object_requests_pending(img_req))
 			return false;
 		*result = img_req->pending_result;
-		img_req->state = RBD_IMG_DONE;
+		WRITE_ONCE(img_req->state, RBD_IMG_DONE);
 		/* fall through */
 	case RBD_IMG_DONE:
 		return true;
@@ -3706,16 +3704,12 @@ static bool __rbd_img_handle_request(struct rbd_img_request *img_req,
 
 	if (need_exclusive_lock(img_req)) {
 		down_read(&rbd_dev->lock_rwsem);
-		mutex_lock(&img_req->state_mutex);
 		done = rbd_img_advance(img_req, result);
 		if (done)
 			rbd_lock_del_request(img_req);
-		mutex_unlock(&img_req->state_mutex);
 		up_read(&rbd_dev->lock_rwsem);
 	} else {
-		mutex_lock(&img_req->state_mutex);
 		done = rbd_img_advance(img_req, result);
-		mutex_unlock(&img_req->state_mutex);
 	}
 
 	if (done && *result) {
@@ -3985,10 +3979,8 @@ static void wake_lock_waiters(struct rbd_device *rbd_dev, int result)
 	}
 
 	list_for_each_entry(img_req, &rbd_dev->acquiring_list, lock_item) {
-		mutex_lock(&img_req->state_mutex);
-		rbd_assert(img_req->state == RBD_IMG_EXCLUSIVE_LOCK);
+		rbd_assert(READ_ONCE(img_req->state) == RBD_IMG_EXCLUSIVE_LOCK);
 		rbd_img_schedule(img_req, result);
-		mutex_unlock(&img_req->state_mutex);
 	}
 
 	list_splice_tail_init(&rbd_dev->acquiring_list, &rbd_dev->running_list);
-- 
2.16.4