[Qemu-devel] Regression on KVM qemu-system-aarch64 since "monitor: enable IO thread for (qmp & !mux) typed"

[Auger Eric]

Hi,

I observe a regression on KVM accelerated qemu-system-aarch64:

Unexpected error in kvm_device_access() at
/home/augere/UPSTREAM/qemu/accel/kvm/kvm-all.c:2164:
2018-03-23T09:59:59.629439Z qemu-system-aarch64: KVM_GET_DEVICE_ATTR
failed: Group 6 attr 0x000000000000c664: Device or resource busy
2018-03-23 10:00:00.085+0000: shutting down, reason=crashed

I did a bisect and it looks the commit that introduces the regression is

"
commit 3fd2457d18edf5736f713dfe1ada9c87a9badab1
Author: Peter Xu <address@hidden>
Date:   Fri Mar 9 17:00:03 2018 +0800

    monitor: enable IO thread for (qmp & !mux) typed

    Start to use dedicate IO thread for QMP monitors that are not using
    MUXed chardev.

    Reviewed-by: Fam Zheng <address@hidden>
    Reviewed-by: Stefan Hajnoczi <address@hidden>
    Signed-off-by: Peter Xu <address@hidden>
    Message-Id: <address@hidden>
    Signed-off-by: Eric Blake <address@hidden>
"

If reverted on top of v2.12.0-rc0, the guest boots fine again. The link
is not obvious though.

Thanks

Eric