[PATCH v2 11/24] block: move drain outside of bdrv_set_backing_hd_drained()

[Fiona Ebner <f.ebner@proxmox.com>]

This is part of resolving the deadlock mentioned in commit "block:
move draining out of bdrv_change_aio_context() and mark GRAPH_RDLOCK".

The function bdrv_set_backing_hd_drained() holds the graph lock, so it
is not allowed to drain. It is called by:
1. bdrv_set_backing_hd(), where a drained section is introduced,
   replacing the previously present bs-specific drains.
2. stream_prepare(), where a drained section is introduced replacing
   the previously present bs-specific drains.

Signed-off-by: Fiona Ebner <f.ebner@proxmox.com>
---

Changes in v2:
* Split up into smaller pieces, flesh out commit messages.

 block.c        | 6 ++----
 block/stream.c | 6 ++----
 2 files changed, 4 insertions(+), 8 deletions(-)

diff --git a/block.c b/block.c
index 702a51ff4b..f323588d15 100644
--- a/block.c
+++ b/block.c
@@ -3569,7 +3569,6 @@ int bdrv_set_backing_hd_drained(BlockDriverState *bs,
         assert(bs->backing->bs->quiesce_counter > 0);
     }
 
-    bdrv_drain_all_begin();
     ret = bdrv_set_file_or_backing_noperm(bs, backing_hd, true, tran, errp);
     if (ret < 0) {
         goto out;
@@ -3578,7 +3577,6 @@ int bdrv_set_backing_hd_drained(BlockDriverState *bs,
     ret = bdrv_refresh_perms(bs, tran, errp);
 out:
     tran_finalize(tran, ret);
-    bdrv_drain_all_end();
     return ret;
 }
 
@@ -3594,11 +3592,11 @@ int bdrv_set_backing_hd(BlockDriverState *bs, BlockDriverState *backing_hd,
     bdrv_graph_rdunlock_main_loop();
 
     bdrv_ref(drain_bs);
-    bdrv_drained_begin(drain_bs);
+    bdrv_drain_all_begin();
     bdrv_graph_wrlock();
     ret = bdrv_set_backing_hd_drained(bs, backing_hd, errp);
     bdrv_graph_wrunlock();
-    bdrv_drained_end(drain_bs);
+    bdrv_drain_all_end();
     bdrv_unref(drain_bs);
 
     return ret;
diff --git a/block/stream.c b/block/stream.c
index 999d9e56d4..6ba49cffd3 100644
--- a/block/stream.c
+++ b/block/stream.c
@@ -80,11 +80,10 @@ static int stream_prepare(Job *job)
      * may end up working with the wrong base node (or it might even have gone
      * away by the time we want to use it).
      */
-    bdrv_drained_begin(unfiltered_bs);
     if (unfiltered_bs_cow) {
         bdrv_ref(unfiltered_bs_cow);
-        bdrv_drained_begin(unfiltered_bs_cow);
     }
+    bdrv_drain_all_begin();
 
     bdrv_graph_rdlock_main_loop();
     base = bdrv_filter_or_cow_bs(s->above_base);
@@ -123,11 +122,10 @@ static int stream_prepare(Job *job)
     }
 
 out:
+    bdrv_drain_all_end();
     if (unfiltered_bs_cow) {
-        bdrv_drained_end(unfiltered_bs_cow);
         bdrv_unref(unfiltered_bs_cow);
     }
-    bdrv_drained_end(unfiltered_bs);
     return ret;
 }
 
-- 
2.39.5