Another AioContext-related issue, and this is a tricky one. Executing a QMP block_resize request for a virtio-blk device running on an iothread may cause a deadlock involving the following mutexes:
- main thead * Has acquired: qemu_mutex_global. * Is trying the acquire: iothread AioContext lock via AIO_WAIT_WHILE (after aio_poll). - iothread * Has acquired: AioContext lock. * Is trying to acquire: qemu_mutex_global (via virtio_notify_config->prepare_mmio_access). With this change, virtio_blk_resize checks if it's being called from a coroutine context running on a non-main thread, and if that's the case, creates a new coroutine and schedules it to be run on the main thread. This works, but means the actual operation is done asynchronously, perhaps opening a window in which a "device_del" operation may fit and remove the VirtIODevice before virtio_notify_config() is executed. I *think* it shouldn't be possible, as BHs will be processed before any new QMP/monitor command, but I'm open to a different approach. RHBZ: https://bugzilla.redhat.com/show_bug.cgi?id=1744955 Signed-off-by: Sergio Lopez <s...@redhat.com> --- hw/block/virtio-blk.c | 25 ++++++++++++++++++++++++- 1 file changed, 24 insertions(+), 1 deletion(-) diff --git a/hw/block/virtio-blk.c b/hw/block/virtio-blk.c index 18851601cb..c763d071f6 100644 --- a/hw/block/virtio-blk.c +++ b/hw/block/virtio-blk.c @@ -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 +1087,33 @@ static int virtio_blk_load_device(VirtIODevice *vdev, QEMUFile *f, return 0; } +static void coroutine_fn virtio_resize_co_entry(void *opaque) +{ + VirtIODevice *vdev = opaque; + + assert(qemu_get_current_aio_context() == qemu_get_aio_context()); + virtio_notify_config(vdev); + aio_wait_kick(); +} + static void virtio_blk_resize(void *opaque) { VirtIODevice *vdev = VIRTIO_DEVICE(opaque); + Coroutine *co; - virtio_notify_config(vdev); + if (qemu_in_coroutine() && + qemu_get_current_aio_context() != qemu_get_aio_context()) { + /* + * virtio_notify_config() needs to acquire the global mutex, + * so calling it from a coroutine running on a non-main context + * may cause a deadlock. Instead, create a new coroutine and + * schedule it to be run on the main thread. + */ + co = qemu_coroutine_create(virtio_resize_co_entry, vdev); + aio_co_schedule(qemu_get_aio_context(), co); + } else { + virtio_notify_config(vdev); + } } static const BlockDevOps virtio_block_ops = { -- 2.21.0