drbd: Ensure that an epoch contains only requests of one kind

The assert in drbd_req.c:755 forces us to have only requests of
one kind in an epoch. The two kinds we distinguish here are:
local-only or mirrored.
Signed-off-by: Philipp Reisner <philipp.reisner@linbit.com>
Signed-off-by: Lars Ellenberg <lars.ellenberg@linbit.com>

drivers/block/drbd/drbd_main.c

@@ -1261,9 +1261,14 @@ __drbd_set_state(struct drbd_conf *mdev, union drbd_state ns,
 	if (os.conn < C_CONNECTED && ns.conn >= C_CONNECTED)
 		drbd_resume_al(mdev);
 
-	if (os.conn == C_AHEAD && ns.conn != C_AHEAD)
+	/* Start a new epoch in case we start to mirror write requests */
+	if (!drbd_should_do_remote(os) && drbd_should_do_remote(ns))
 		tl_forget(mdev);
 
+	/* Do not add local-only requests to an epoch with mirrored requests */
+	if (drbd_should_do_remote(os) && !drbd_should_do_remote(ns))
+		set_bit(CREATE_BARRIER, &mdev->flags);
+
 	ascw = kmalloc(sizeof(*ascw), GFP_ATOMIC);
 	if (ascw) {
 		ascw->os = os;

drivers/block/drbd/drbd_req.c

@@ -762,27 +762,6 @@ static int drbd_may_do_local_read(struct drbd_conf *mdev, sector_t sector, int s
 	return 0 == drbd_bm_count_bits(mdev, sbnr, ebnr);
 }
 
-static bool drbd_should_do_remote(struct drbd_conf *mdev)
-{
-	union drbd_state s = mdev->state;
-
-	return s.pdsk == D_UP_TO_DATE ||
-		(s.pdsk >= D_INCONSISTENT &&
-		 s.conn >= C_WF_BITMAP_T &&
-		 s.conn < C_AHEAD);
-	/* Before proto 96 that was >= CONNECTED instead of >= C_WF_BITMAP_T.
-	   That is equivalent since before 96 IO was frozen in the C_WF_BITMAP*
-	   states. */
-}
-static bool drbd_should_send_oos(struct drbd_conf *mdev)
-{
-	union drbd_state s = mdev->state;
-
-	return s.conn == C_AHEAD || s.conn == C_WF_BITMAP_S;
-	/* pdsk = D_INCONSISTENT as a consequence. Protocol 96 check not necessary
-	   since we enter state C_AHEAD only if proto >= 96 */
-}
-
 static int drbd_make_request_common(struct drbd_conf *mdev, struct bio *bio, unsigned long start_time)
 {
 	const int rw = bio_rw(bio);
@@ -854,8 +833,8 @@ static int drbd_make_request_common(struct drbd_conf *mdev, struct bio *bio, uns
 		drbd_al_begin_io(mdev, sector);
 	}
 
-	remote = remote && drbd_should_do_remote(mdev);
-	send_oos = rw == WRITE && drbd_should_send_oos(mdev);
+	remote = remote && drbd_should_do_remote(mdev->state);
+	send_oos = rw == WRITE && drbd_should_send_oos(mdev->state);
 	D_ASSERT(!(remote && send_oos));
 
 	if (!(local || remote) && !is_susp(mdev->state)) {
@@ -896,8 +875,8 @@ static int drbd_make_request_common(struct drbd_conf *mdev, struct bio *bio, uns
 	}
 
 	if (remote || send_oos) {
-		remote = drbd_should_do_remote(mdev);
-		send_oos = rw == WRITE && drbd_should_send_oos(mdev);
+		remote = drbd_should_do_remote(mdev->state);
+		send_oos = rw == WRITE && drbd_should_send_oos(mdev->state);
 		D_ASSERT(!(remote && send_oos));
 
 		if (!(remote || send_oos))

drivers/block/drbd/drbd_req.h

@@ -360,4 +360,22 @@ static inline int req_mod(struct drbd_request *req,
 
 	return rv;
 }
+
+static inline bool drbd_should_do_remote(union drbd_state s)
+{
+	return s.pdsk == D_UP_TO_DATE ||
+		(s.pdsk >= D_INCONSISTENT &&
+		 s.conn >= C_WF_BITMAP_T &&
+		 s.conn < C_AHEAD);
+	/* Before proto 96 that was >= CONNECTED instead of >= C_WF_BITMAP_T.
+	   That is equivalent since before 96 IO was frozen in the C_WF_BITMAP*
+	   states. */
+}
+static inline bool drbd_should_send_oos(union drbd_state s)
+{
+	return s.conn == C_AHEAD || s.conn == C_WF_BITMAP_S;
+	/* pdsk = D_INCONSISTENT as a consequence. Protocol 96 check not necessary
+	   since we enter state C_AHEAD only if proto >= 96 */
+}
+
 #endif