From 399ed639cc85835eb7a4a7241df6c1741c0578ba Mon Sep 17 00:00:00 2001
From: Kevin Wolf <kwolf@redhat.com>
Date: Fri, 1 Mar 2019 14:27:44 +0100
Subject: [PATCH 2/9] virtio-blk: Increase in_flight for request restart BH

RH-Author: Kevin Wolf <kwolf@redhat.com>
Message-id: <20190301142747.12251-3-kwolf@redhat.com>
Patchwork-id: 84762
O-Subject: [RHEL-7.7 qemu-kvm-rhev PATCH 2/5] virtio-blk: Increase in_flight for request restart BH
Bugzilla: 1671173
RH-Acked-by: Stefan Hajnoczi <stefanha@redhat.com>
RH-Acked-by: Paolo Bonzini <pbonzini@redhat.com>
RH-Acked-by: John Snow <jsnow@redhat.com>

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 <kwolf@redhat.com>
(cherry picked from commit 680f200217748e0920b79ec1d524717c2f50935b)
Signed-off-by: Kevin Wolf <kwolf@redhat.com>
Signed-off-by: Miroslav Rezanina <mrezanin@redhat.com>
---
 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);
     aio_context_release(blk_get_aio_context(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);
         qemu_bh_schedule(s->bh);
     }
 }
-- 
1.8.3.1