diff --git a/block/io.c b/block/io.c
index d76202b4522a5f2ba6dfd935ab881c5254faa2f1..4a598299a92184a5071289b5a6f0196ca7c01c97 100644
--- a/block/io.c
+++ b/block/io.c
@@ -501,7 +501,8 @@ static void dummy_bh_cb(void *opaque)
 
 void bdrv_wakeup(BlockDriverState *bs)
 {
-    if (bs->wakeup) {
+    /* The barrier (or an atomic op) is in the caller.  */
+    if (atomic_read(&bs->wakeup)) {
         aio_bh_schedule_oneshot(qemu_get_aio_context(), dummy_bh_cb, NULL);
     }
 }
diff --git a/block/nfs.c b/block/nfs.c
index 848b2c0bb0ac94ed1d293319f80d8d40e233f26f..18c87d2f2535e6e749fbe0eb592405bc5044580c 100644
--- a/block/nfs.c
+++ b/block/nfs.c
@@ -730,7 +730,9 @@ nfs_get_allocated_file_size_cb(int ret, struct nfs_context *nfs, void *data,
     if (task->ret < 0) {
         error_report("NFS Error: %s", nfs_get_error(nfs));
     }
-    task->complete = 1;
+
+    /* Set task->complete before reading bs->wakeup.  */
+    atomic_mb_set(&task->complete, 1);
     bdrv_wakeup(task->bs);
 }
 
diff --git a/block/sheepdog.c b/block/sheepdog.c
index a18315a1cabe24a9da3b440f238dc9ca5fdc8e85..5ebf5d9fbb11985251b4a526a68fc2f3227cfd73 100644
--- a/block/sheepdog.c
+++ b/block/sheepdog.c
@@ -698,7 +698,8 @@ out:
 
     srco->co = NULL;
     srco->ret = ret;
-    srco->finished = true;
+    /* Set srco->finished before reading bs->wakeup.  */
+    atomic_mb_set(&srco->finished, true);
     if (srco->bs) {
         bdrv_wakeup(srco->bs);
     }
diff --git a/include/block/block.h b/include/block/block.h
index 9b355e92d814886762cdc8be5e3513c81d5ae47b..a4f09df95ad319461cda1004113426dfb2489786 100644
--- a/include/block/block.h
+++ b/include/block/block.h
@@ -402,7 +402,8 @@ void bdrv_drain_all(void);
          * block_job_defer_to_main_loop for how to do it). \
          */                                                \
         assert(!bs_->wakeup);                              \
-        bs_->wakeup = true;                                \
+        /* Set bs->wakeup before evaluating cond.  */      \
+        atomic_mb_set(&bs_->wakeup, true);                 \
         while (busy_) {                                    \
             if ((cond)) {                                  \
                 waited_ = busy_ = true;                    \
@@ -414,7 +415,7 @@ void bdrv_drain_all(void);
                 waited_ |= busy_;                          \
             }                                              \
         }                                                  \
-        bs_->wakeup = false;                               \
+        atomic_set(&bs_->wakeup, false);                   \
     }                                                      \
     waited_; })
 
diff --git a/include/block/block_int.h b/include/block/block_int.h
index 39be34af5c984336a58b65e45254f4f9cc145417..cf544b7f3106ddf4c9633aa657812f4be6ea8cc9 100644
--- a/include/block/block_int.h
+++ b/include/block/block_int.h
@@ -604,8 +604,6 @@ struct BlockDriverState {
     /* Callback before write request is processed */
     NotifierWithReturnList before_write_notifiers;
 
-    bool wakeup;
-
     /* Offset after the highest byte written to */
     uint64_t wr_highest_offset;
 
@@ -636,6 +634,11 @@ struct BlockDriverState {
     unsigned int in_flight;
     unsigned int serialising_in_flight;
 
+    /* Internal to BDRV_POLL_WHILE and bdrv_wakeup.  Accessed with atomic
+     * ops.
+     */
+    bool wakeup;
+
     /* do we need to tell the quest if we have a volatile write cache? */
     int enable_write_cache;