qemu-kvm/kvm-block-Drop-out-of-coroutine-in-bdrv_do_drained_begin.patch

From 9a789d104a4a69031ad95d7fad6380ab21e82503 Mon Sep 17 00:00:00 2001
From: Kevin Wolf <kwolf@redhat.com>
Date: Fri, 18 Nov 2022 18:41:08 +0100
Subject: [PATCH 26/31] block: Drop out of coroutine in
 bdrv_do_drained_begin_quiesce()

RH-Author: Stefano Garzarella <sgarzare@redhat.com>
RH-MergeRequest: 135: block: Simplify drain to prevent QEMU from crashing during snapshot
RH-Bugzilla: 2155112
RH-Acked-by: Emanuele Giuseppe Esposito <eesposit@redhat.com>
RH-Acked-by: Hanna Czenczek <hreitz@redhat.com>
RH-Acked-by: Kevin Wolf <kwolf@redhat.com>
RH-Commit: [14/16] c9266663b822f703e55b6a07de98ceb56e69e924 (sgarzarella/qemu-kvm-c-9-s)

The next patch adds a parent drain to bdrv_attach_child_common(), which
shouldn't be, but is currently called from coroutines in some cases (e.g.
.bdrv_co_create implementations generally open new nodes). Therefore,
the assertion that we're not in a coroutine doesn't hold true any more.

We could just remove the assertion because there is nothing in the
function that should be in conflict with running in a coroutine, but
just to be on the safe side, we can reverse the caller relationship
between bdrv_do_drained_begin() and bdrv_do_drained_begin_quiesce() so
that the latter also just drops out of coroutine context and we can
still be certain in the future that any drain code doesn't run in
coroutines.

As a nice side effect, the structure of bdrv_do_drained_begin() is now
symmetrical with bdrv_do_drained_end().

Signed-off-by: Kevin Wolf <kwolf@redhat.com>
Message-Id: <20221118174110.55183-14-kwolf@redhat.com>
Reviewed-by: Hanna Reitz <hreitz@redhat.com>
Reviewed-by: Vladimir Sementsov-Ogievskiy <vsementsov@yandex-team.ru>
Signed-off-by: Kevin Wolf <kwolf@redhat.com>
(cherry picked from commit 05c272ff0cf1b16cc3606f746182dd99b774f553)
Signed-off-by: Stefano Garzarella <sgarzare@redhat.com>
---
 block/io.c | 25 ++++++++++++-------------
 1 file changed, 12 insertions(+), 13 deletions(-)

diff --git a/block/io.c b/block/io.c
index 2e9503df6a..5e9150d92c 100644
--- a/block/io.c
+++ b/block/io.c
@@ -346,10 +346,15 @@ static void coroutine_fn bdrv_co_yield_to_drain(BlockDriverState *bs,
     }
 }
 
-void bdrv_do_drained_begin_quiesce(BlockDriverState *bs, BdrvChild *parent)
+static void bdrv_do_drained_begin(BlockDriverState *bs, BdrvChild *parent,
+                                  bool poll)
 {
     IO_OR_GS_CODE();
-    assert(!qemu_in_coroutine());
+
+    if (qemu_in_coroutine()) {
+        bdrv_co_yield_to_drain(bs, true, parent, poll);
+        return;
+    }
 
     /* Stop things in parent-to-child order */
     if (qatomic_fetch_inc(&bs->quiesce_counter) == 0) {
@@ -359,17 +364,6 @@ void bdrv_do_drained_begin_quiesce(BlockDriverState *bs, BdrvChild *parent)
             bs->drv->bdrv_drain_begin(bs);
         }
     }
-}
-
-static void bdrv_do_drained_begin(BlockDriverState *bs, BdrvChild *parent,
-                                  bool poll)
-{
-    if (qemu_in_coroutine()) {
-        bdrv_co_yield_to_drain(bs, true, parent, poll);
-        return;
-    }
-
-    bdrv_do_drained_begin_quiesce(bs, parent);
 
     /*
      * Wait for drained requests to finish.
@@ -385,6 +379,11 @@ static void bdrv_do_drained_begin(BlockDriverState *bs, BdrvChild *parent,
     }
 }
 
+void bdrv_do_drained_begin_quiesce(BlockDriverState *bs, BdrvChild *parent)
+{
+    bdrv_do_drained_begin(bs, parent, false);
+}
+
 void bdrv_drained_begin(BlockDriverState *bs)
 {
     IO_OR_GS_CODE();
-- 
2.31.1