Commit 9b92fbcf authored by Sergio Lopez's avatar Sergio Lopez Committed by Stefan Hajnoczi
Browse files

virtio-blk: schedule virtio_notify_config to run on main context 



virtio_notify_config() needs to acquire the global mutex, which isn't
allowed from an iothread, and may lead to a deadlock like this:

 - main thead
  * Has acquired: qemu_global_mutex.
  * Is trying the acquire: iothread AioContext lock via
    AIO_WAIT_WHILE (after aio_poll).

 - iothread
  * Has acquired: AioContext lock.
  * Is trying to acquire: qemu_global_mutex (via
    virtio_notify_config->prepare_mmio_access).

If virtio_blk_resize() is called from an iothread, schedule
virtio_notify_config() to be run in the main context BH.

[Removed unnecessary newline as suggested by Kevin Wolf
<kwolf@redhat.com>.
--Stefan]

Signed-off-by: default avatarSergio Lopez <slp@redhat.com>
Reviewed-by: default avatarKevin Wolf <kwolf@redhat.com>
Message-id: 20190916112411.21636-1-slp@redhat.com
Message-Id: <20190916112411.21636-1-slp@redhat.com>
Signed-off-by: default avatarStefan Hajnoczi <stefanha@redhat.com>
parent d38d6de2

hw/block/virtio-blk.c

+15 −1
Original line number Diff line number Diff line
@@ -16,6 +16,7 @@ 
#include "qemu/iov.h"

#include "qemu/module.h"

#include "qemu/error-report.h"

#include "qemu/main-loop.h"

#include "trace.h"

#include "hw/block/block.h"

#include "hw/qdev-properties.h"
@@ -1086,11 +1087,24 @@ static int virtio_blk_load_device(VirtIODevice *vdev, QEMUFile *f, 
    return 0;

}



static void virtio_resize_cb(void *opaque)

{

    VirtIODevice *vdev = opaque;



    assert(qemu_get_current_aio_context() == qemu_get_aio_context());

    virtio_notify_config(vdev);

}



static void virtio_blk_resize(void *opaque)

{

    VirtIODevice *vdev = VIRTIO_DEVICE(opaque);



    virtio_notify_config(vdev);

    /*

     * virtio_notify_config() needs to acquire the global mutex,

     * so it can't be called from an iothread. Instead, schedule

     * it to be run in the main context BH.

     */

    aio_bh_schedule_oneshot(qemu_get_aio_context(), virtio_resize_cb, vdev);

}



static const BlockDevOps virtio_block_ops = {