drbd: Do not send two barriers without any writes between them

Signed-off-by: Philipp Reisner <philipp.reisner@linbit.com>
Signed-off-by: Lars Ellenberg <lars.ellenberg@linbit.com>

1 files changed, 7 insertions, 2 deletions

diff --git a/drivers/block/drbd/drbd_main.c b/drivers/block/drbd/drbd_main.c
index a8a0341fce53..7d359863ae32 100644
--- a/drivers/block/drbd/drbd_main.c
+++ b/drivers/block/drbd/drbd_main.c
@@ -344,7 +344,7 @@ bail:
 static void _tl_restart(struct drbd_conf *mdev, enum drbd_req_event what)
 {
         struct drbd_tl_epoch *b, *tmp, **pn;
-        struct list_head *le, *tle;
+        struct list_head *le, *tle, carry_reads;
         struct drbd_request *req;
         int rv, n_writes, n_reads;
 
@@ -353,6 +353,7 @@ static void _tl_restart(struct drbd_conf *mdev, enum drbd_req_event what)
         while (b) {
                 n_writes = 0;
                 n_reads = 0;
+                INIT_LIST_HEAD(&carry_reads);
                 list_for_each_safe(le, tle, &b->requests) {
                         req = list_entry(le, struct drbd_request, tl_requests);
                         rv = _req_mod(req, what);
@@ -362,7 +363,7 @@ static void _tl_restart(struct drbd_conf *mdev, enum drbd_req_event what)
                 }
                 tmp = b->next;
 
-                if (n_writes + n_reads) {
+                if (n_writes) {
                         if (what == resend) {
                                 b->n_writes = n_writes;
                                 if (b->w.cb == NULL) {
@@ -375,6 +376,8 @@ static void _tl_restart(struct drbd_conf *mdev, enum drbd_req_event what)
                         }
                         pn = &b->next;
                 } else {
+                        if (n_reads)
+                                list_add(&carry_reads, &b->requests);
                         /* there could still be requests on that ring list,
                          * in case local io is still pending */
                         list_del(&b->requests);
@@ -389,6 +392,7 @@ static void _tl_restart(struct drbd_conf *mdev, enum drbd_req_event what)
                                 /* recycle, but reinit! */
                                 D_ASSERT(tmp == NULL);
                                 INIT_LIST_HEAD(&b->requests);
+                                list_splice(&carry_reads, &b->requests);
                                 INIT_LIST_HEAD(&b->w.list);
                                 b->w.cb = NULL;
                                 b->br_number = net_random();
@@ -401,6 +405,7 @@ static void _tl_restart(struct drbd_conf *mdev, enum drbd_req_event what)
                         kfree(b);
                 }
                 b = tmp;
+                list_splice(&carry_reads, &b->requests);
         }
 }