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List-Archive: List-Post: List-Help: List-Subscribe: , Cc: kwolf@redhat.com, mreitz@redhat.com, qemu-devel@nongnu.org, stefanha@redhat.com, mst@redhat.com Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" On 9/13/19 6:56 AM, Sergio Lopez wrote: > 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. > > Signed-off-by: Sergio Lopez > --- > Changelog > > v2: > - Use aio_bh_schedule_oneshot instead of scheduling a coroutine > (thanks Kevin Wolf). > - Switch from RFC to v2 patch. > --- > hw/block/virtio-blk.c | 21 ++++++++++++++++++++- > 1 file changed, 20 insertions(+), 1 deletion(-) > > diff --git a/hw/block/virtio-blk.c b/hw/block/virtio-blk.c > index 18851601cb..669dc60f5b 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 +1087,29 @@ 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); > + if (qemu_get_current_aio_context() != qemu_get_aio_context()) { > + /* > + * 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); > + } else { > + virtio_notify_config(vdev); > + } > } > > static const BlockDevOps virtio_block_ops = { > Do we need to bother to check our current context before firing off the oneshot? It's simpler to just fire off the oneshot. I can't imagine that resize is a hot path that needs to worry about being that efficient. Well, I guess it doesn't hurt either. Reviewed-by: John Snow