From c56d4b513e1a0b868b788ea495857f41cde1acf6 Mon Sep 17 00:00:00 2001
From: Kevin Wolf <kwolf@redhat.com>
Date: Wed, 10 Oct 2018 20:21:41 +0100
Subject: [PATCH 15/49] block: Don't poll in parent drain callbacks

RH-Author: Kevin Wolf <kwolf@redhat.com>
Message-id: <20181010202213.7372-3-kwolf@redhat.com>
Patchwork-id: 82592
O-Subject: [RHEL-8 qemu-kvm PATCH 12/44] block: Don't poll in parent drain callbacks
Bugzilla: 1637976
RH-Acked-by: Max Reitz <mreitz@redhat.com>
RH-Acked-by: John Snow <jsnow@redhat.com>
RH-Acked-by: Thomas Huth <thuth@redhat.com>

bdrv_do_drained_begin() is only safe if we have a single
BDRV_POLL_WHILE() after quiescing all affected nodes. We cannot allow
that parent callbacks introduce a nested polling loop that could cause
graph changes while we're traversing the graph.

Split off bdrv_do_drained_begin_quiesce(), which only quiesces a single
node without waiting for its requests to complete. These requests will
be waited for in the BDRV_POLL_WHILE() call down the call chain.

Signed-off-by: Kevin Wolf <kwolf@redhat.com>
(cherry picked from commit dcf94a23b1add0f856db51e9ff5ba0774e096076)
Signed-off-by: Kevin Wolf <kwolf@redhat.com>
Signed-off-by: Danilo C. L. de Paula <ddepaula@redhat.com>
---
 block.c               |  2 +-
 block/io.c            | 24 ++++++++++++++++--------
 include/block/block.h |  9 +++++++++
 3 files changed, 26 insertions(+), 9 deletions(-)

diff --git a/block.c b/block.c
index 9afaf26..5a50de6 100644
--- a/block.c
+++ b/block.c
@@ -818,7 +818,7 @@ static char *bdrv_child_get_parent_desc(BdrvChild *c)
 static void bdrv_child_cb_drained_begin(BdrvChild *child)
 {
     BlockDriverState *bs = child->opaque;
-    bdrv_drained_begin(bs);
+    bdrv_do_drained_begin_quiesce(bs, NULL);
 }
 
 static bool bdrv_child_cb_drained_poll(BdrvChild *child)
diff --git a/block/io.c b/block/io.c
index 442ded1..9c41ff9 100644
--- a/block/io.c
+++ b/block/io.c
@@ -285,15 +285,10 @@ static void coroutine_fn bdrv_co_yield_to_drain(BlockDriverState *bs,
     assert(data.done);
 }
 
-void bdrv_do_drained_begin(BlockDriverState *bs, bool recursive,
-                           BdrvChild *parent, bool poll)
+void bdrv_do_drained_begin_quiesce(BlockDriverState *bs,
+                                   BdrvChild *parent)
 {
-    BdrvChild *child, *next;
-
-    if (qemu_in_coroutine()) {
-        bdrv_co_yield_to_drain(bs, true, recursive, parent, poll);
-        return;
-    }
+    assert(!qemu_in_coroutine());
 
     /* Stop things in parent-to-child order */
     if (atomic_fetch_inc(&bs->quiesce_counter) == 0) {
@@ -302,6 +297,19 @@ void bdrv_do_drained_begin(BlockDriverState *bs, bool recursive,
 
     bdrv_parent_drained_begin(bs, parent);
     bdrv_drain_invoke(bs, true);
+}
+
+static void bdrv_do_drained_begin(BlockDriverState *bs, bool recursive,
+                                  BdrvChild *parent, bool poll)
+{
+    BdrvChild *child, *next;
+
+    if (qemu_in_coroutine()) {
+        bdrv_co_yield_to_drain(bs, true, recursive, parent, poll);
+        return;
+    }
+
+    bdrv_do_drained_begin_quiesce(bs, parent);
 
     if (recursive) {
         bs->recursive_quiesce_counter++;
diff --git a/include/block/block.h b/include/block/block.h
index 2bbea7c..43f29b5 100644
--- a/include/block/block.h
+++ b/include/block/block.h
@@ -619,6 +619,15 @@ bool bdrv_drain_poll(BlockDriverState *bs, bool recursive,
 void bdrv_drained_begin(BlockDriverState *bs);
 
 /**
+ * bdrv_do_drained_begin_quiesce:
+ *
+ * Quiesces a BDS like bdrv_drained_begin(), but does not wait for already
+ * running requests to complete.
+ */
+void bdrv_do_drained_begin_quiesce(BlockDriverState *bs,
+                                   BdrvChild *parent);
+
+/**
  * Like bdrv_drained_begin, but recursively begins a quiesced section for
  * exclusive access to all child nodes as well.
  */
-- 
1.8.3.1