4 files changed, 23 insertions, 8 deletions

diff --git a/drivers/block/drbd/drbd_actlog.c b/drivers/block/drbd/drbd_actlog.c
index 6ace11e9e5a1..3fbef018ce55 100644
--- a/drivers/block/drbd/drbd_actlog.c
+++ b/drivers/block/drbd/drbd_actlog.c
@@ -876,7 +876,11 @@ int __drbd_set_out_of_sync(struct drbd_conf *mdev, sector_t sector, int size,
         unsigned int enr, count = 0;
         struct lc_element *e;
 
-        if (size <= 0 || (size & 0x1ff) != 0 || size > DRBD_MAX_BIO_SIZE) {
+        /* this should be an empty REQ_FLUSH */
+        if (size == 0)
+                return 0;
+
+        if (size < 0 || (size & 0x1ff) != 0 || size > DRBD_MAX_BIO_SIZE) {
                 dev_err(DEV, "sector: %llus, size: %d\n",
                         (unsigned long long)sector, size);
                 return 0;
diff --git a/drivers/block/drbd/drbd_main.c b/drivers/block/drbd/drbd_main.c
index 1ee1404769c2..2e0e7fc1dbba 100644
--- a/drivers/block/drbd/drbd_main.c
+++ b/drivers/block/drbd/drbd_main.c
@@ -3636,6 +3636,7 @@ struct drbd_conf *drbd_new_device(unsigned int minor)
         q->backing_dev_info.congested_data = mdev;
 
         blk_queue_make_request(q, drbd_make_request);
+        blk_queue_flush(q, REQ_FLUSH | REQ_FUA);
         /* Setting the max_hw_sectors to an odd value of 8kibyte here
            This triggers a max_bio_size message upon first attach or connect */
         blk_queue_max_hw_sectors(q, DRBD_MAX_BIO_SIZE_SAFE >> 8);
diff --git a/drivers/block/drbd/drbd_receiver.c b/drivers/block/drbd/drbd_receiver.c
index 83d99133f94b..c74ca2df7431 100644
--- a/drivers/block/drbd/drbd_receiver.c
+++ b/drivers/block/drbd/drbd_receiver.c
@@ -277,6 +277,9 @@ static void drbd_pp_free(struct drbd_conf *mdev, struct page *page, int is_net)
         atomic_t *a = is_net ? &mdev->pp_in_use_by_net : &mdev->pp_in_use;
         int i;
 
+        if (page == NULL)
+                return;
+
         if (drbd_pp_vacant > (DRBD_MAX_BIO_SIZE/PAGE_SIZE)*minor_count)
                 i = page_chain_free(page);
         else {
@@ -316,7 +319,7 @@ struct drbd_epoch_entry *drbd_alloc_ee(struct drbd_conf *mdev,
                                      gfp_t gfp_mask) __must_hold(local)
 {
         struct drbd_epoch_entry *e;
-        struct page *page;
+        struct page *page = NULL;
         unsigned nr_pages = (data_size + PAGE_SIZE -1) >> PAGE_SHIFT;
 
         if (drbd_insert_fault(mdev, DRBD_FAULT_AL_EE))
@@ -329,9 +332,11 @@ struct drbd_epoch_entry *drbd_alloc_ee(struct drbd_conf *mdev,
                 return NULL;
         }
 
-        page = drbd_pp_alloc(mdev, nr_pages, (gfp_mask & __GFP_WAIT));
-        if (!page)
-                goto fail;
+        if (data_size) {
+                page = drbd_pp_alloc(mdev, nr_pages, (gfp_mask & __GFP_WAIT));
+                if (!page)
+                        goto fail;
+        }
 
         INIT_HLIST_NODE(&e->collision);
         e->epoch = NULL;
@@ -1270,7 +1275,6 @@ read_in_block(struct drbd_conf *mdev, u64 id, sector_t sector, int data_size) __
 
         data_size -= dgs;
 
-        ERR_IF(data_size == 0) return NULL;
         ERR_IF(data_size &  0x1ff) return NULL;
         ERR_IF(data_size >  DRBD_MAX_BIO_SIZE) return NULL;
 
@@ -1291,6 +1295,9 @@ read_in_block(struct drbd_conf *mdev, u64 id, sector_t sector, int data_size) __
         if (!e)
                 return NULL;
 
+        if (!data_size)
+                return e;
+
         ds = data_size;
         page = e->pages;
         page_chain_for_each(page) {
@@ -1715,6 +1722,10 @@ static int receive_Data(struct drbd_conf *mdev, enum drbd_packets cmd, unsigned
 
         dp_flags = be32_to_cpu(p->dp_flags);
         rw |= wire_flags_to_bio(mdev, dp_flags);
+        if (e->pages == NULL) {
+                D_ASSERT(e->size == 0);
+                D_ASSERT(dp_flags & DP_FLUSH);
+        }
 
         if (dp_flags & DP_MAY_SET_IN_SYNC)
                 e->flags |= EE_MAY_SET_IN_SYNC;
diff --git a/drivers/block/drbd/drbd_req.c b/drivers/block/drbd/drbd_req.c
index 1f4b2dbb7d4a..910335c30927 100644
--- a/drivers/block/drbd/drbd_req.c
+++ b/drivers/block/drbd/drbd_req.c
@@ -1111,13 +1111,12 @@ void drbd_make_request(struct request_queue *q, struct bio *bio)
         /*
          * what we "blindly" assume:
          */
-        D_ASSERT(bio->bi_size > 0);
         D_ASSERT((bio->bi_size & 0x1ff) == 0);
 
         /* to make some things easier, force alignment of requests within the
          * granularity of our hash tables */
         s_enr = bio->bi_sector >> HT_SHIFT;
-        e_enr = (bio->bi_sector+(bio->bi_size>>9)-1) >> HT_SHIFT;
+        e_enr = bio->bi_size ? (bio->bi_sector+(bio->bi_size>>9)-1) >> HT_SHIFT : s_enr;
 
         if (likely(s_enr == e_enr)) {
                 do {