debian/patches/extra/0002-virtio-blk-schedule-virtio_notify_config-to-run-on-m.patch

   1 From 0000000000000000000000000000000000000000 Mon Sep 17 00:00:00 2001
   2 From: Sergio Lopez <slp@redhat.com>
   3 Date: Mon, 16 Sep 2019 13:24:12 +0200
   4 Subject: [PATCH] virtio-blk: schedule virtio_notify_config to run on main
   5  context
   6
   7 virtio_notify_config() needs to acquire the global mutex, which isn't
   8 allowed from an iothread, and may lead to a deadlock like this:
   9
  10  - main thead
  11   * Has acquired: qemu_global_mutex.
  12   * Is trying the acquire: iothread AioContext lock via
  13     AIO_WAIT_WHILE (after aio_poll).
  14
  15  - iothread
  16   * Has acquired: AioContext lock.
  17   * Is trying to acquire: qemu_global_mutex (via
  18     virtio_notify_config->prepare_mmio_access).
  19
  20 If virtio_blk_resize() is called from an iothread, schedule
  21 virtio_notify_config() to be run in the main context BH.
  22
  23 [Removed unnecessary newline as suggested by Kevin Wolf
  24 <kwolf@redhat.com>.
  25 --Stefan]
  26
  27 Signed-off-by: Sergio Lopez <slp@redhat.com>
  28 Reviewed-by: Kevin Wolf <kwolf@redhat.com>
  29 Message-id: 20190916112411.21636-1-slp@redhat.com
  30 Message-Id: <20190916112411.21636-1-slp@redhat.com>
  31 Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
  32 ---
  33  hw/block/virtio-blk.c | 16 +++++++++++++++-
  34  1 file changed, 15 insertions(+), 1 deletion(-)
  35
  36 diff --git a/hw/block/virtio-blk.c b/hw/block/virtio-blk.c
  37 index cbb3729158..0d9adcdaff 100644
  38 --- a/hw/block/virtio-blk.c
  39 +++ b/hw/block/virtio-blk.c
  40 @@ -16,6 +16,7 @@
  41  #include "qemu/iov.h"
  42  #include "qemu/module.h"
  43  #include "qemu/error-report.h"
  44 +#include "qemu/main-loop.h"
  45  #include "trace.h"
  46  #include "hw/block/block.h"
  47  #include "sysemu/blockdev.h"
  48 @@ -1082,11 +1083,24 @@ static int virtio_blk_load_device(VirtIODevice *vdev, QEMUFile *f,
  49      return 0;
  50  }
  51
  52 +static void virtio_resize_cb(void *opaque)
  53 +{
  54 +    VirtIODevice *vdev = opaque;
  55 +
  56 +    assert(qemu_get_current_aio_context() == qemu_get_aio_context());
  57 +    virtio_notify_config(vdev);
  58 +}
  59 +
  60  static void virtio_blk_resize(void *opaque)
  61  {
  62      VirtIODevice *vdev = VIRTIO_DEVICE(opaque);
  63
  64 -    virtio_notify_config(vdev);
  65 +    /*
  66 +     * virtio_notify_config() needs to acquire the global mutex,
  67 +     * so it can't be called from an iothread. Instead, schedule
  68 +     * it to be run in the main context BH.
  69 +     */
  70 +    aio_bh_schedule_oneshot(qemu_get_aio_context(), virtio_resize_cb, vdev);
  71  }
  72
  73  static const BlockDevOps virtio_block_ops = {
  74 --
  75 2.20.1
  76