Re: [PATCH 1/2] vhost-user: add a write-read lock

[Peter Xu]

On Thu, Jul 11, 2024 at 06:44:23PM +0530, Prasad Pandit wrote:
> From: Prasad Pandit <pjp@fedoraproject.org>
> 
> QEMU threads use vhost_user_write/read calls to send
> and receive messages from a vhost-user device. When multiple
> threads communicate with the same vhost-user device, they can
> receive each other's messages, resulting in an erroneous state.
> 
>  vhost_user_read_header:
>   700871,700871: Failed to read msg header. Flags 0x0 instead of 0x5.
>  vhost_device_iotlb_miss:
>   700871,700871: Fail to update device iotlb
>  vhost_user_postcopy_end:
>   700871,700900: Failed to receive reply to postcopy_end
>  vhost_user_read_header:
>   700871,700871: Failed to read msg header. Flags 0x0 instead of 0x5.
> 
> Here fault thread seems to end the postcopy migration while
> another thread is starting the vhost-user device.
> 
> Add a rw lock to hold for one vhost_user_write/read cycle
> and avoid such race conditions.
> 
> Suggested-by: Peter Xu <peterx@redhat.com>
> Signed-off-by: Prasad Pandit <pjp@fedoraproject.org>
> ---
>  hw/virtio/vhost-user.c         | 423 +++++++++++++++++++--------------
>  include/hw/virtio/vhost-user.h |   3 +

I apologize if I suggested WITH_QEMU_LOCK_GUARD when we talked.. I don't
remember which one I suggested, but in this case IIUC it'll be much easier
to review if you use the other sister function QEMU_LOCK_GUARD()
instead.. That should make the diff much, much less.

-- 
Peter Xu