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From 2f11a1952881d9e2dcc8acb3549441dbd9ade1e3 Mon Sep 17 00:00:00 2001
From: Kevin Wolf <>
Date: Wed, 14 Aug 2019 08:42:26 +0100
Subject: [PATCH 03/10] virtio-blk: Increase in_flight for request restart BH

RH-Author: Kevin Wolf <>
Message-id: <>
Patchwork-id: 89967
O-Subject: [RHEL-8.1.0 qemu-kvm PATCH 2/5] virtio-blk: Increase in_flight for request restart BH
Bugzilla: 1716349
RH-Acked-by: Stefan Hajnoczi <>
RH-Acked-by: Max Reitz <>
RH-Acked-by: Paolo Bonzini <>

virtio_blk_dma_restart_bh() submits new requests, so in order to make
sure that these requests are not started inside a drained section of the
attached BlockBackend, we need to make sure that draining the
BlockBackend waits for the BH to be executed.

This BH is still questionable because its scheduled in the main thread
instead of the configured iothread. Leave a FIXME comment for this.

But with this fix, enabling the data plane at least waits for these
requests (in bdrv_set_aio_context()) instead of changing the AioContext
under their feet and making them run in the wrong thread, causing
crashes and failures (e.g. due to missing locking).

Signed-off-by: Kevin Wolf <>
(cherry picked from commit 680f200217748e0920b79ec1d524717c2f50935b)
Signed-off-by: Kevin Wolf <>
Signed-off-by: Danilo C. L. de Paula <>
 hw/block/virtio-blk.c | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/hw/block/virtio-blk.c b/hw/block/virtio-blk.c
index b1532e4..691ade4 100644
--- a/hw/block/virtio-blk.c
+++ b/hw/block/virtio-blk.c
@@ -678,6 +678,7 @@ static void virtio_blk_dma_restart_bh(void *opaque)
     if (mrb.num_reqs) {
         virtio_blk_submit_multireq(s->blk, &mrb);
+    blk_dec_in_flight(s->conf.conf.blk);
@@ -691,8 +692,11 @@ static void virtio_blk_dma_restart_cb(void *opaque, int running,
     if (!s->bh) {
+        /* FIXME The data plane is not started yet, so these requests are
+         * processed in the main thread. */
         s->bh = aio_bh_new(blk_get_aio_context(s->conf.conf.blk),
                            virtio_blk_dma_restart_bh, s);
+        blk_inc_in_flight(s->conf.conf.blk);