diff --git a/block/sheepdog.c b/block/sheepdog.c
index bd7cbed048..9585beb73e 100644
--- a/block/sheepdog.c
+++ b/block/sheepdog.c
@@ -318,6 +318,10 @@ enum AIOCBState {
     AIOCB_DISCARD_OBJ,
 };
 
+#define AIOCBOverwrapping(x, y)                                 \
+    (!(x->max_affect_data_idx < y->min_affect_data_idx          \
+       || y->max_affect_data_idx < x->min_affect_data_idx))
+
 struct SheepdogAIOCB {
     BlockAIOCB common;
 
@@ -334,6 +338,11 @@ struct SheepdogAIOCB {
 
     bool cancelable;
     int nr_pending;
+
+    uint32_t min_affect_data_idx;
+    uint32_t max_affect_data_idx;
+
+    QLIST_ENTRY(SheepdogAIOCB) aiocb_siblings;
 };
 
 typedef struct BDRVSheepdogState {
@@ -362,8 +371,10 @@ typedef struct BDRVSheepdogState {
 
     /* Every aio request must be linked to either of these queues. */
     QLIST_HEAD(inflight_aio_head, AIOReq) inflight_aio_head;
-    QLIST_HEAD(pending_aio_head, AIOReq) pending_aio_head;
     QLIST_HEAD(failed_aio_head, AIOReq) failed_aio_head;
+
+    CoQueue overwrapping_queue;
+    QLIST_HEAD(inflight_aiocb_head, SheepdogAIOCB) inflight_aiocb_head;
 } BDRVSheepdogState;
 
 static const char * sd_strerror(int err)
@@ -498,13 +509,7 @@ static void sd_aio_cancel(BlockAIOCB *blockacb)
     AIOReq *aioreq, *next;
 
     if (sd_acb_cancelable(acb)) {
-        /* Remove outstanding requests from pending and failed queues.  */
-        QLIST_FOREACH_SAFE(aioreq, &s->pending_aio_head, aio_siblings,
-                           next) {
-            if (aioreq->aiocb == acb) {
-                free_aio_req(s, aioreq);
-            }
-        }
+        /* Remove outstanding requests from failed queue.  */
         QLIST_FOREACH_SAFE(aioreq, &s->failed_aio_head, aio_siblings,
                            next) {
             if (aioreq->aiocb == acb) {
@@ -529,6 +534,10 @@ static SheepdogAIOCB *sd_aio_setup(BlockDriverState *bs, QEMUIOVector *qiov,
                                    int64_t sector_num, int nb_sectors)
 {
     SheepdogAIOCB *acb;
+    uint32_t object_size;
+    BDRVSheepdogState *s = bs->opaque;
+
+    object_size = (UINT32_C(1) << s->inode.block_size_shift);
 
     acb = qemu_aio_get(&sd_aiocb_info, bs, NULL, NULL);
 
@@ -542,6 +551,11 @@ static SheepdogAIOCB *sd_aio_setup(BlockDriverState *bs, QEMUIOVector *qiov,
     acb->coroutine = qemu_coroutine_self();
     acb->ret = 0;
     acb->nr_pending = 0;
+
+    acb->min_affect_data_idx = acb->sector_num * BDRV_SECTOR_SIZE / object_size;
+    acb->max_affect_data_idx = (acb->sector_num * BDRV_SECTOR_SIZE +
+                              acb->nb_sectors * BDRV_SECTOR_SIZE) / object_size;
+
     return acb;
 }
 
@@ -703,38 +717,6 @@ static int reload_inode(BDRVSheepdogState *s, uint32_t snapid, const char *tag);
 static int get_sheep_fd(BDRVSheepdogState *s, Error **errp);
 static void co_write_request(void *opaque);
 
-static AIOReq *find_pending_req(BDRVSheepdogState *s, uint64_t oid)
-{
-    AIOReq *aio_req;
-
-    QLIST_FOREACH(aio_req, &s->pending_aio_head, aio_siblings) {
-        if (aio_req->oid == oid) {
-            return aio_req;
-        }
-    }
-
-    return NULL;
-}
-
-/*
- * This function searchs pending requests to the object `oid', and
- * sends them.
- */
-static void coroutine_fn send_pending_req(BDRVSheepdogState *s, uint64_t oid)
-{
-    AIOReq *aio_req;
-    SheepdogAIOCB *acb;
-
-    while ((aio_req = find_pending_req(s, oid)) != NULL) {
-        acb = aio_req->aiocb;
-        /* move aio_req from pending list to inflight one */
-        QLIST_REMOVE(aio_req, aio_siblings);
-        QLIST_INSERT_HEAD(&s->inflight_aio_head, aio_req, aio_siblings);
-        add_aio_request(s, aio_req, acb->qiov->iov, acb->qiov->niov,
-                        acb->aiocb_type);
-    }
-}
-
 static coroutine_fn void reconnect_to_sdog(void *opaque)
 {
     BDRVSheepdogState *s = opaque;
@@ -840,12 +822,6 @@ static void coroutine_fn aio_read_response(void *opaque)
                 s->max_dirty_data_idx = MAX(idx, s->max_dirty_data_idx);
                 s->min_dirty_data_idx = MIN(idx, s->min_dirty_data_idx);
             }
-            /*
-             * Some requests may be blocked because simultaneous
-             * create requests are not allowed, so we search the
-             * pending requests here.
-             */
-            send_pending_req(s, aio_req->oid);
         }
         break;
     case AIOCB_READ_UDATA:
@@ -1341,30 +1317,6 @@ out:
     return ret;
 }
 
-/* Return true if the specified request is linked to the pending list. */
-static bool check_simultaneous_create(BDRVSheepdogState *s, AIOReq *aio_req)
-{
-    AIOReq *areq;
-    QLIST_FOREACH(areq, &s->inflight_aio_head, aio_siblings) {
-        if (areq != aio_req && areq->oid == aio_req->oid) {
-            /*
-             * Sheepdog cannot handle simultaneous create requests to the same
-             * object, so we cannot send the request until the previous request
-             * finishes.
-             */
-            DPRINTF("simultaneous create to %" PRIx64 "\n", aio_req->oid);
-            aio_req->flags = 0;
-            aio_req->base_oid = 0;
-            aio_req->create = false;
-            QLIST_REMOVE(aio_req, aio_siblings);
-            QLIST_INSERT_HEAD(&s->pending_aio_head, aio_req, aio_siblings);
-            return true;
-        }
-    }
-
-    return false;
-}
-
 static void coroutine_fn resend_aioreq(BDRVSheepdogState *s, AIOReq *aio_req)
 {
     SheepdogAIOCB *acb = aio_req->aiocb;
@@ -1379,10 +1331,6 @@ static void coroutine_fn resend_aioreq(BDRVSheepdogState *s, AIOReq *aio_req)
             goto out;
         }
 
-        if (check_simultaneous_create(s, aio_req)) {
-            return;
-        }
-
         if (s->inode.data_vdi_id[idx]) {
             aio_req->base_oid = vid_to_data_oid(s->inode.data_vdi_id[idx], idx);
             aio_req->flags |= SD_FLAG_CMD_COW;
@@ -1458,8 +1406,8 @@ static int sd_open(BlockDriverState *bs, QDict *options, int flags,
     filename = qemu_opt_get(opts, "filename");
 
     QLIST_INIT(&s->inflight_aio_head);
-    QLIST_INIT(&s->pending_aio_head);
     QLIST_INIT(&s->failed_aio_head);
+    QLIST_INIT(&s->inflight_aiocb_head);
     s->fd = -1;
 
     memset(vdi, 0, sizeof(vdi));
@@ -1524,6 +1472,7 @@ static int sd_open(BlockDriverState *bs, QDict *options, int flags,
     bs->total_sectors = s->inode.vdi_size / BDRV_SECTOR_SIZE;
     pstrcpy(s->name, sizeof(s->name), vdi);
     qemu_co_mutex_init(&s->lock);
+    qemu_co_queue_init(&s->overwrapping_queue);
     qemu_opts_del(opts);
     g_free(buf);
     return 0;
@@ -2195,12 +2144,6 @@ static int coroutine_fn sd_co_rw_vector(void *p)
                                 old_oid, done);
         QLIST_INSERT_HEAD(&s->inflight_aio_head, aio_req, aio_siblings);
 
-        if (create) {
-            if (check_simultaneous_create(s, aio_req)) {
-                goto done;
-            }
-        }
-
         add_aio_request(s, aio_req, acb->qiov->iov, acb->qiov->niov,
                         acb->aiocb_type);
     done:
@@ -2215,6 +2158,20 @@ out:
     return 1;
 }
 
+static bool check_overwrapping_aiocb(BDRVSheepdogState *s, SheepdogAIOCB *aiocb)
+{
+    SheepdogAIOCB *cb;
+
+    QLIST_FOREACH(cb, &s->inflight_aiocb_head, aiocb_siblings) {
+        if (AIOCBOverwrapping(aiocb, cb)) {
+            return true;
+        }
+    }
+
+    QLIST_INSERT_HEAD(&s->inflight_aiocb_head, aiocb, aiocb_siblings);
+    return false;
+}
+
 static coroutine_fn int sd_co_writev(BlockDriverState *bs, int64_t sector_num,
                         int nb_sectors, QEMUIOVector *qiov)
 {
@@ -2234,14 +2191,25 @@ static coroutine_fn int sd_co_writev(BlockDriverState *bs, int64_t sector_num,
     acb->aio_done_func = sd_write_done;
     acb->aiocb_type = AIOCB_WRITE_UDATA;
 
+retry:
+    if (check_overwrapping_aiocb(s, acb)) {
+        qemu_co_queue_wait(&s->overwrapping_queue);
+        goto retry;
+    }
+
     ret = sd_co_rw_vector(acb);
     if (ret <= 0) {
+        QLIST_REMOVE(acb, aiocb_siblings);
+        qemu_co_queue_restart_all(&s->overwrapping_queue);
         qemu_aio_unref(acb);
         return ret;
     }
 
     qemu_coroutine_yield();
 
+    QLIST_REMOVE(acb, aiocb_siblings);
+    qemu_co_queue_restart_all(&s->overwrapping_queue);
+
     return acb->ret;
 }
 
@@ -2250,19 +2218,30 @@ static coroutine_fn int sd_co_readv(BlockDriverState *bs, int64_t sector_num,
 {
     SheepdogAIOCB *acb;
     int ret;
+    BDRVSheepdogState *s = bs->opaque;
 
     acb = sd_aio_setup(bs, qiov, sector_num, nb_sectors);
     acb->aiocb_type = AIOCB_READ_UDATA;
     acb->aio_done_func = sd_finish_aiocb;
 
+retry:
+    if (check_overwrapping_aiocb(s, acb)) {
+        qemu_co_queue_wait(&s->overwrapping_queue);
+        goto retry;
+    }
+
     ret = sd_co_rw_vector(acb);
     if (ret <= 0) {
+        QLIST_REMOVE(acb, aiocb_siblings);
+        qemu_co_queue_restart_all(&s->overwrapping_queue);
         qemu_aio_unref(acb);
         return ret;
     }
 
     qemu_coroutine_yield();
 
+    QLIST_REMOVE(acb, aiocb_siblings);
+    qemu_co_queue_restart_all(&s->overwrapping_queue);
     return acb->ret;
 }
 
@@ -2610,14 +2589,25 @@ static coroutine_fn int sd_co_discard(BlockDriverState *bs, int64_t sector_num,
     acb->aiocb_type = AIOCB_DISCARD_OBJ;
     acb->aio_done_func = sd_finish_aiocb;
 
+retry:
+    if (check_overwrapping_aiocb(s, acb)) {
+        qemu_co_queue_wait(&s->overwrapping_queue);
+        goto retry;
+    }
+
     ret = sd_co_rw_vector(acb);
     if (ret <= 0) {
+        QLIST_REMOVE(acb, aiocb_siblings);
+        qemu_co_queue_restart_all(&s->overwrapping_queue);
         qemu_aio_unref(acb);
         return ret;
     }
 
     qemu_coroutine_yield();
 
+    QLIST_REMOVE(acb, aiocb_siblings);
+    qemu_co_queue_restart_all(&s->overwrapping_queue);
+
     return acb->ret;
 }
 
diff --git a/block/ssh.c b/block/ssh.c
index aebb18cc8f..8d0673903d 100644
--- a/block/ssh.c
+++ b/block/ssh.c
@@ -563,7 +563,7 @@ static int connect_to_ssh(BDRVSSHState *s, QDict *options,
     /* Open the socket and connect. */
     s->sock = inet_connect(s->hostport, errp);
     if (s->sock < 0) {
-        ret = -errno;
+        ret = -EIO;
         goto err;
     }